Biological Anthropology Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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- A -

abdominal wall defect  click this icon to hear the preceding term pronounced
a genetically inherited condition in which intestines and other abdominal organs protrude through the central abdominal wall.  This must be corrected by surgery at birth.
ABO click this icon to hear the preceding term pronounced blood system
a human blood typing system in which there are 4 distinct types: A, B, AB, and O.  An individual inherits an ABO type from his or her parents and does not change it throughout life.  The ABO system is not unique to humans but is shared by many other primates including apes and monkeys.  Humans and other primates share other blood typing systems as well.
accelerator mass spectrometer  click this icon to hear the preceding term pronounced   (AMS)
a research instrument primarily used in physics to accelerate streams of charged subnuclear particles to high velocities in order to sort and analyze them.  This technique is now also used to count carbon isotope atoms for radiocarbon dating.  The advantage of this technique over the conventional radiocarbon method is that it requires a far smaller sample size and can potentially provide dates going back to around 100,000 B.P.  At present, however, AMS dates generally are for events less than 60,000 years old.
acclimatization  click this icon to hear the preceding term pronounced
changes in the body in response to environmental stresses such as high or low temperatures, intense ultraviolet radiation from sun light, or high altitude.  The anatomical and physiological changes made in acclimatization are usually reversible.
Acheulian click this icon to hear the preceding term pronounced tool tradition
the most well known stone tool making tradition of Homo erectus and early archaic humans.  It first appeared about 1.5 million years ago or somewhat earlier in East Africa and eventually spread throughout Africa, Southern Europe, and South Asia.  The most diagnostic Acheulian artifact is the hand ax.
adaptation  click this icon to hear the preceding term pronounced
the process by which populations of organisms respond to long term environmental stresses by permanent genetic change--i.e., by evolving.  See adjustment.
adaptive radiation  click this icon to hear the preceding term pronounced
the relatively rapid expansion and diversification of an evolving group of organisms as they adapt to new ecological niches.  Adaptive radiation is the process by which one species evolves into two or more species.  This occurs as a result of different populations becoming reproductively isolated from each other, usually by adapting to different environments.  The branching pattern of evolution resulting from adaptive radiation is known as cladogenesis click this icon to hear the preceding term pronounced.
adjustment
the process by which individual organisms respond to environmental stresses during their lifetime without changing genetically.  Adjustments are generally not inheritable.  Acclimatization and developmental adjustment are examples of adjustment.  See adaptation.
agglutination  click this icon to hear the preceding term pronounced
the clumping together of red cells in blood as a result of antibodies attaching to antigens on the surface of the cells.  This occurs when blood of incompatible types is mixed together outside of the body, as for example during blood typing.  When different types of blood come into contact within the body as a result of a mismatched transfusion, the alien red cells usually burst instead of agglutinate.
agonistic display  click this icon to hear the preceding term pronounced
a threatening gesture, stare, pose, or display intended to intimidate others.
AIDS  click this icon to hear the preceding term pronounced   (Acquired Immunodeficiency Deficiency Syndrome)
a slow acting disease caused by the HIV retrovirus.  AIDS is usually fatal if not treated.  Important disease-fighting white blood cells are destroyed, resulting in a weakened immune system.  Death usually comes as a result of cancer or other diseases that are normally fought off by healthy immune systems.  HIV is spread from person to person via bodily fluids such as blood and semen.  The common methods of transmission are via sexual intercourse or sharing hypodermic needles.
albinism  click this icon to hear the preceding term pronounced
the genetically inherited condition in which there is a marked deficiency of pigmentation in skin, hair, and eyes.  An individual with these traits is an "albino."  Since the gene for albinism is recessive, it only shows up in the phenotype of homozygous recessive people.  Albinos have sunlight sensitive eyes and skin.  They are also more likely to develop skin and eye cancers.  This is a pleiotropic trait.

allele  click this icon to hear the preceding term pronounced

an alternate form or variety of a gene.   The alleles for a trait occupy the same locus or position on homologous chromosomes and thus govern the same trait.  However, because they are different, their action may result in different expressions of that trait.
Allen's Rule  click this icon to hear the preceding term pronounced
within the same species of warm-blooded animals, individuals from populations living in colder environments usually have shorter appendages than do those from populations in warmer areas.  This is because of the selective advantage it provides.  Short arms, legs, and other appendages have relatively less skin surface area that can radiate heat into the surrounding environment.  Subsequently, the body retains more of it.   Allen's Rule is a corollary of Bergmann's Rule.  Allen's  Rule was named after Joel Allen, a 19th century naturalist. 
allogrooming  click this icon to hear the preceding term pronounced
the common primate practice of carefully picking through the hair of someone, looking for insects, twigs, and other debris.  Grooming others is a common way by which primates communicate affection and reduce group tension.  See autogrooming.
alpha-feto protein (AFP) sampling  click this icon to hear the preceding term pronounced
a routine diagnostic procedure for pregnant women to determine whether or not their fetuses have gross chromosomal anomalies.  This screening procedure is also called maternal serum alpha-feto protein (MSAFP) testing.  The testing is comparatively inexpensive but not as reliable as amniocentesis or chorionic villi sampling.  With AFP sampling, blood is drawn from a pregnant woman in order to determine the amount of alpha-feto protein that has leaked into her system from her unborn child.  Unusually high or low amounts of AFP relative to the stage of pregnancy indicate that there may be specific kinds of genetic defects.  Specifically, it may indicate the likelihood of Down syndrome, neural tube defects, abdominal wall defects, and trisomy 18.  Low AFP levels are associated with Down syndrome, while high levels are indicative of neural tube defects.  The amounts of other diagnostic fetal chemicals (hCG and estriol) also are measured in expanded AFP screening or triple-screening.
alpha male click this icon to hear the preceding term pronounced and alpha female
the adult male and female members of a community who are at the top of their gender based dominance hierarchies.  Non-human primate alpha males and females usually mate more frequently and have greater access to food.
alpha particle  click this icon to hear the preceding term pronounced
a kind of positively charged subnuclear particle (consisting of 2 protons and 2 neutrons) given off by some isotopes when they decay or fission.
Alzheimer syndrome  click this icon to hear the preceding term pronounced
a progressive, irreversible disease characterized by degeneration of brain cells that commonly result in severe loss of memory, the ability to think, and pay attention.  There are also usually major changes in personality.   Alzheimer syndrome most often occurs in late middle and old age.  Genetic factors probably play a role since this syndrome is more common in some families. 
amino acid  click this icon to hear the preceding term pronounced
an organic molecule that is a building blocks of proteins.  There are at least 20 different kinds of amino acids in living things.  Proteins are composed of different combinations of amino acids assembled in chain-like molecules.  Amino acids are primarily composed of carbon, oxygen, hydrogen, and nitrogen.
amino acid racemization click this icon to hear the preceding term pronounced dating
a method for dating organic matter that is based on the fact that amino acids progressively change to mirror image forms following the death of an organism--i.e., from L-amino acid to D-amino acid forms.  Aspartic acid in organic samples is commonly used for this dating technique.  Amino acid racemization could be considered to be a chronometric or a calibrated relative dating method.
Amish  click this icon to hear the preceding term pronounced
members of a conservative Protestant sect related to the Mennonites.  The Amish migrated to Pennsylvania from Switzerland in the late 18th century.  The Old Order Amish are a relatively closed group that shuns most modern conveniences in their farming lifestyle.  They use horse drawn carriages, dress very simply, and reject those who marry non-Amish.
amniocentesis  click this icon to hear the preceding term pronounced
a diagnostic procedure for pregnant women to determine whether or not their fetuses have gross chromosomal anomalies.  It involves sampling the liquid immediately surrounding a fetus within the amnion.  This amniotic fluid is extracted through the mother's abdominal and uterine walls with a hypodermic needle.  The amniotic fluid mostly contains fetal urine but also has millions of fetal skin cells that can be cultured to produce a karyotype.  There is 99+% accuracy in diagnosing Down syndrome and most other gross chromosomal aberrations including neural tube defects such as spina bifida.
amnion  click this icon to hear the preceding term pronounced
the innermost membrane of the flexible sac enclosing a fetus.  It is filled with amniotic fluid, which helps cushion the fetus and protect it from injury.  See cervix for an illustration.
amniote  click this icon to hear the preceding term pronounced
referring to an egg with a hard shell and protective membranes that prevent the embryo from rapidly drying out.  Reptiles, birds, and prototherian mammals lay amniote eggs.
amniotic fluid  click this icon to hear the preceding term pronounced
the fluid surrounding a fetus inside an amniotic sac.  It mostly consists of fetal urine, but also contains some fetal skin cells.  See cervix for an illustration.
Amphibia  click this icon to hear the preceding term pronounced
the class of vertebrates that includes frogs, toads, and salamanders.  Amphibians spend part of their lives under water and part on land.  They must return to damp areas to reproduce since their eggs would otherwise dry out.  They start life with gills, like fish, and later develop lungs to breath air.
anaerobic  click this icon to hear the preceding term pronounced
without oxygen
anagenesis  click this icon to hear the preceding term pronounced
The pattern of non-branching evolution that results from successive speciation in a single evolutionary line.
analogies  click this icon to hear the preceding term pronounced
anatomical features that have the same form or function in different species that have no known common ancestor.  Analogies are also referred to as analogous structures or features.
analogous structures  click this icon to hear the preceding term pronounced
see analogies.

anatomy  click this icon to hear the preceding term pronounced

referring to the structural parts of organisms.  See physiology.
anemia  click this icon to hear the preceding term pronounced
a medical condition characterized by fatigue, weakness, poor appetite, weight loss, and paleness or a yellowish tinge to the skin and eyes resulting from a deficiency of red blood cells or insufficient amounts of hemoglobin molecules within the red cells.  The result in both cases is a significantly reduced ability to get oxygen to the cells of the body.  There are many different genetic and environmental causes of anemia.
anencephaly  click this icon to hear the preceding term pronounced
the failure to develop a brain at the end of the spinal chord.   This type of neural tube defect always causes the death of a fetus or newborn child.
aneuploidy  click this icon to hear the preceding term pronounced
a chromosomal abnormality in which there is an addition or loss of chromosomes within a set (e.g., 23 + 22 or 23 + 24).  Down syndrome is most often the result of this kind of error.  See monosomy, trisomy, and polyploidy.

Angelman syndrome  click this icon to hear the preceding term pronounced

a rare genetically inherited form of mental retardation.  The inheritance of this syndrome is subject to genome imprinting.
angle of declination  click this icon to hear the preceding term pronounced
the degree difference between the direction of magnetic north and rotational north at a particular location.
Animalia  click this icon to hear the preceding term pronounced
the kingdom of living things that includes all animals. They are multicellular organisms that ingest food rather than absorb or photosynthesize it.  They also have their own means of locomotion in at least one phase of their life cycles.
anterior  click this icon to hear the preceding term pronounced
see dorsal.
anthropoid  click this icon to hear the preceding term pronounced
an animal within the primate suborder Anthropoidea click this icon to hear the preceding term pronounced.  Monkeys, apes, and humans are anthropoids.

antibody  click this icon to hear the preceding term pronounced

a kind of protein produced by the body to identify and neutralize or destroy alien antigens.  Antibodies are involved in the rejection of mismatched blood transfusions and organ transplants.  They are also responsible for recognizing and eliminating bacteria and viruses.  Antibodies provide a major defense for our bodies against invasion by alien organisms.

anticodons  click this icon to hear the preceding term pronounced

sequences of three nucleotide bases on a transfer RNA molecule that can pair with a specific messenger RNA Codon.

antigen  click this icon to hear the preceding term pronounced

molecules that provide the specific signature or identity to blood or other tissue cells.  When alien antigens are introduced into the body, they stimulate the production and mobilization of antibodies.  Antigens are found on the surface of blood and other tissue cells as well as bacteria and viruses.
apparent temperature
what the air temperature actually feels like to people.  This varies with the relative humidity of the air.  The higher the relative humidity, the higher the apparent temperature is even if the air temperature does not change because evaporation of sweat is progressively less efficient in cooling the body.
arboreal  click this icon to hear the preceding term pronounced
tree-living; referring to animals that are adapted to life in the trees.  Arboreal animals spend most of their time scampering around in trees rather than on the ground, in the air, or water.  See semi-terrestrial and terrestrial.
archaeology  click this icon to hear the preceding term pronounced
the study of the prehistory or early history of societies and their cultures.  Unlike paleoanthropology, the focus of archaeology is mainly on the material remains of culture rather than biological evolution.
archaeomagnetic click this icon to hear the preceding term pronounced dating
See paleomagnetic dating.
archaic humans
the variety or species of humans that was intermediate between Homo erectus and modern humans.  The earliest archaic humans may have appeared shortly after 800,000 years ago in Southern Europe and East Africa.  Elsewhere in the Old World, the transition to archaic humans began around 400,000 years ago or later.  The most well known late archaic humans were the Neandertals.  Archaic humans are also known as archaic Homo sapiens click this icon to hear the preceding term pronounced and premodern humans.  See Homo heidelbergensis.
argon-40/argon-39 click this icon to hear the preceding term pronounced dating   (40Ar/39Ar)
a radiometric dating method based on the changing ratio of argon-40 to argon-39  with the passage of time in volcanic rock or ash.  This technique was derived from potassium-argon dating.  The argon-40/argon-39 method is usually more accurate than potassium-argon dating and doesn't require as large a sample.
arthritis  click this icon to hear the preceding term pronounced
a degenerative disease characterized by chronic inflammation of the joints and accompanying pain. 
artifact  click this icon to hear the preceding term pronounced
a thing that is intentionally made according to a cultural pattern or inadvertently modified as a result of culturally patterned behavior.  Artifacts are usually relatively portable objects such as projectile points, ceramic pots, and baskets.
artifact time marker
an artifact type that was made by a particular culture during a limited time period.  When discovered clearly in association with ancient humans in an archaeological site, they are an indication of at least the relative time of the occupation.  When the independent dating of the artifact types is reliable, this can be considered a calibrated relative dating method.
assimilation model
a hypothesis to explain the origin of modern Homo sapiens.  It proposes that the first modern humans evolved in Africa, but when they migrated into other regions they did not simply replace existing human populations.  Rather, they interbred to a limited degree with late archaic humans resulting in hybrid populations.  The assimilation model is also known as the "partial replacement model."  See replacement model and regional continuity model.
atlatl  click this icon to hear the preceding term pronounced
see spear thrower.
australopithecine  click this icon to hear the preceding term pronounced
a species of the genus Australopithecus.   They lived during the Pliocene and early Pleistocene geological Epochs in Africa (i.e., ca. 4.2-1.4 million years ago).  Australopithecines and humans are hominins.  One or more species of australopithecines probably were our ancestors.
Australopithecus  click this icon to hear the preceding term pronounced
see australopithecines
autogrooming  click this icon to hear the preceding term pronounced
grooming oneself in contrast to allogrooming.
autoimmune disorder  click this icon to hear the preceding term pronounced
any of several disorders in which one's antibodies attack his/her own body tissues.  Lupus erythematosus, rheumatoid arthritis, and even common allergies are caused by such autoimmune reactions.
atomic mass
the mass number of one atom of an isotope (e.g., carbon-14).  It is the sum of the number of protons and neutrons in the nucleus of one atom.  See atomic number.
atomic number
the number of protons in the nucleus of one atom of an element.  See atomic mass.

autosome  click this icon to hear the preceding term pronounced

any chromosome other than a sex chromosome.  Human somatic cells have 22 pairs of autosomes and 1 pair of sex chromosomes.
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- B -

bacteria  click this icon to hear the preceding term pronounced
microscopic simple single celled organisms lacking chlorophyll and a membrane around their nuclei.  They reproduce by mitosis.  Many species of bacteria are parasites of humans and other animals and plants.  Bacteria are classified as members of the Kingdom Monera.  
balanced polymorphism  click this icon to hear the preceding term pronounced
the maintenance of two or more alleles for a trait in a population at a more or less constant frequency ratio due to the selective advantage of heterozygotes.  See polymorphism.
basal metabolic rate  click this icon to hear the preceding term pronounced
the measure of the total energy utilized by the body to maintain its necessary processes while at rest.  Those processes include  keeping the heart, brain, and other organs functioning normally and the necessary replacement of old or damaged cells.  About 75% of the food energy that we burn every day is used for these functions.  The remaining energy is used to fuel physical work or is stored in fat reserves for when it is needed.  Basal metabolic rate also refers to the minimum level of heat produced by the body at rest.
Bergmann's Rule  click this icon to hear the preceding term pronounced
within the same species of warm-blooded animals, individuals from populations living in colder environments usually have greater body mass than do those from populations in warmer areas.  This is because of the selective advantage it provides.  A massive body produces more internal heat and radiates relatively less of it into the surrounding environment because the skin surface area is relatively smaller.  Subsequently, a massive body produces and retains more heat.    Bergmann's Rule was named after Carl Bergmann, a 19th century naturalist.  See Allen's Rule.
Beringia  click this icon to hear the preceding term pronounced
the intercontinental land connection appeared between Siberia and Alaska that appeared at least twice during the last ice age as a result of sea levels dropping more than 300 feet.  Beringia is also known as the Bering Plain.
Bering Plain
see Beringia.
beta particle  click this icon to hear the preceding term pronounced
a kind of energy charged subnuclear particle (consisting of an electron or a positron) given off by some isotopes when they decay or fission.
biface  click this icon to hear the preceding term pronounced
a stone tool that is shaped on two faces or sides.  Hand axes are examples of bifaces.  See uniface.
big game hunting
a specialized subsistence pattern based primarily on hunting large animals, especially herbivorous herding mammals such as horses, reindeer, bison, and elephants.
bilaterally symmetrical  click this icon to hear the preceding term pronounced
the chordate characteristic of the left and right sides of the body being mirror images of each other.  If there are two functionally similar body parts, they are usually found roughly equidistant from the center line, parallel to each other on bilaterally symmetrical animals.
bilirubin  click this icon to hear the preceding term pronounced
the yellow-red pigment of human bile.  Small amounts of it are normally found in blood and urine.  At high bilirubin levels, blood and urine change color and the skin becomes yellow or jaundiced.  This is one of the symptoms of mismatched blood transfusions and mother-fetus incompatibility in blood type.
binocular vision  click this icon to hear the preceding term pronounced
seeing with two eyes that have an overlapping field of view.  This is essential to stereoscopic vision.
binomen  click this icon to hear the preceding term pronounced
the Linnaean classification system use of two Latin name categories, genus and species, to designate each type of organism.  A genus is a higher level category that includes one or more species under it.  For example, humans are Homo sapiens, or "man who is wise"--Homo is our genus and sapiens is our species.  Binomen literally means "two names" in Latin.  Binomial nomenclature is another term for binomen. 
binomial nomenclature  click this icon to hear the preceding term pronounced
see binomen.
biocultural evolution  click this icon to hear the preceding term pronounced
the pattern of human evolution in which the effects of natural selection are altered by cultural inventions.  Culture can alter the direction of evolution by creating non-biological adaptations to environmental stresses (e.g., wearing insulating clothes on very cold days).  This potentially reduces the need to evolve genetic responses to the stresses.  This has meant that we have been able to remain essentially tropical animals biologically and live in colder regions of our planet.  Biocultural evolution can also involve a mutual, interactive evolution of human biology and culture.   An example of this has been the selection favoring sickle-cell trait in Africa.  Human agricultural practices altered the environment, which resulted in factors that were advantageous to both the malarial microorganisms and the mosquitoes that transmit them between people.  This, in turn, selected for the sickling allele. 
biopsy  click this icon to hear the preceding term pronounced
the process of removing a tissue sample from a living organism for diagnostic examination (e.g., chorionic villi sampling).
biospecies  click this icon to hear the preceding term pronounced
a species that has been defined on the basis of the ability to produce fertile offspring.  Members of the same species can produce offspring that can in turn reproduce while members of different species cannot.  See morphospecies.
biostratigraphy  click this icon to hear the preceding term pronounced
the relative dating of early human sites by association with index fossils uncovered in the same strata as human evidence.  The assumption is that both the people and the species that is now an index fossil must have lived at about the same time.
bipedalism  click this icon to hear the preceding term pronounced
referring to walking and running on two feet.  Humans are the only fully bipedal primates today.
blade flake  click this icon to hear the preceding term pronounced
a thin, roughly parallel-sided stone flake that is at least twice as long as it is wide.  They were made out of brittle breaking materials such as flint click this icon to hear the preceding term pronounced, chert click this icon to hear the preceding term pronounced, and obsidian click this icon to hear the preceding term pronounced.  Blade flakes were preforms for the manufacture of many different kinds of tools during the Upper Paleolithic--e.g., knives, hide scrapers, spear tips, drills, awls, and burins.  See punch flaking.

blending theory

an incorrect 19th century theory about the inheritance of characteristics.  It proposed that inherited traits blend from generation to generation.  Through his plant cross-breeding experiments, Gregor Mendel proved that this was wrong.
body language
gestures, postures, and facial expressions used to communicate nonverbally.

bottleneck effect

a dramatic reduction in genetic diversity of a population or species resulting from an ecological crisis that wipes out most of its members.  The limited genetic diversity of the few survivors is the pool from which all future generations are based.  This is one of the small population size effects.
B.P. date  click this icon to hear the preceding term pronounced
a chronometric date that is measured in years before the present.  By convention, scientists have assigned 1950 A.D. in the Gregorian calendar as the present.
brachiator  click this icon to hear the preceding term pronounced
an animal that travels through the trees by swinging under branches with a hand over hand motion.  The smaller apes and some New World monkeys brachiate.  Brachiation is also referred to as suspensory climbing.
Broca's area  click this icon to hear the preceding term pronounced
a small area of the human brain that controls the production of speech.  It is located in the left frontal lobe of the cerebral cortex click this icon to hear the preceding term pronounced.  See Wernicke's area.

bubonic plague  click this icon to hear the preceding term pronounced

a highly contagious disease caused by the bacterium Yersinia pestis.  It is normally spread by fleas that have taken blood from an infected human or other animal.  Symptoms include a high fever and extremely swollen lymph nodes in the groin, armpits, and/or throat.  An agonizing death usually occurs within a few days.
bull roarer
a musical instrument or noise maker consisting of a flat, elongated oval slab of rock, bone, or wood with a hole in one end through which a string is attached.  When it is twisted and then whirled rapidly by the string, a humming or "roaring" noise is produced.  Bull roarers may be only a few inches in length or several feet long.
burin  click this icon to hear the preceding term pronounced
narrow gouging chisels used to make and shape a host of other implements out of bone, tusks, antler, or wood.  They were usually made from blade flakes in the late Upper Paleolithic tool traditions. 

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- C -

calibrated relative dating
use of a relative dating method that measures somewhat irregular occurring natural phenomena that have been cross-dated with at least one chronometric technique so that the dates are somewhat comparable from sites in one region to another.  Calibrated relative methods could be considered to be somewhere between ordinary relative methods and radiometric methods in terms of their ability to produce dates that closely approximate the actual date of a sample.  Amino acid racemization and paleomagnetic dating are generally considered to be either chronometric or calibrated relative methods. 
canine click this icon to hear the preceding term pronounced teeth
the comparatively pointed teeth on either side of the incisors, at the front of the mouth of mammals.  There is one canine tooth in each of the four quadrants of the mouth.  Canine teeth are mainly used to pierce and tear food.  See molar and premolar teeth.
canine diastema    click this icon to hear the preceding term pronounced
a space or gap between the canine and adjacent teeth.  It allows room for the point of the protruding opposite canine tooth and thereby permits the upper and lower teeth to bite together.  Normally, there is a diastema opposite each of the four canine teeth if the canines are significantly longer than the other teeth.
capillaries  click this icon to hear the preceding term pronounced
the hair thin blood vessels connecting small branches of arteries and veins that form a vascular network throughout the body of animals.
carbohydrate  click this icon to hear the preceding term pronounced
a class of organic molecules that include sugars and starches.
carbon-14 dating   (C-14 click this icon to hear the preceding term pronounced)
see radiocarbon dating.
carnivorous  click this icon to hear the preceding term pronounced
eating only meat.  Animals that have this sort of diet are carnivores.  See herbivorous and omnivorous.
carotene  click this icon to hear the preceding term pronounced
any of several reddish-orange organic pigments.  While carotene is present in human skin, it is also found in higher concentrations in butter, carrots, and some other vegetables.  Carotene is involved in the synthesis of vitamin A in people and other animals.
carrier
an individual who is heterozygous for a trait that only shows up in the phenotype of those who are homozygous recessive.  Carriers often do not show any signs of the trait but can pass it on to their offspring.  This is the case with hemophilia.
cataract  click this icon to hear the preceding term pronounced
an impairment of vision caused by the lenses of the eyes becoming cloudy.  Cataracts are common in elderly people.  They may be inherited or caused by diabetes and environmental factors.
catastrophism  click this icon to hear the preceding term pronounced
the view that the Earth's geological landscape is the result of violent cataclysmic events.  Advocates of this theory usually believe that there have been a number of wide-spread violent and sudden natural catastrophes that have destroyed most living things.  This idea was used by George Cuvier to explain the extinction of species.   Catastrophism was opposed by uniformitarianism during the late 18th and 19th centuries.
Caucasoid  click this icon to hear the preceding term pronounced   (or Caucasian click this icon to hear the preceding term pronounced)
a presumed human "race" consisting of Europeans and other closely related people. The classification is based on the discredited typological model.  The term "Caucasoid" was derived from the Caucasus Mountains on the southeast fringe of Europe between the Black and Caspian Seas.  This region was once thought to be the homeland of Indo-Europeans.
cell  click this icon to hear the preceding term pronounced
a complex unit of protoplasm, usually with a nucleus, cytoplasm, and an enclosing membrane. All plants and animals are composed of one or more microscopic cells.  The smallest organic unit capable of carrying out all of the functions normally attributed to life is a cell.  See eukaryotic cell and prokaryotic cell.
cell membrane  click this icon to hear the preceding term pronounced
the selectively permeable membrane enclosing a cell.
Cenozoic Era  click this icon to hear the preceding term pronounced
the most recent geological era, dating from about 65.5 million years ago to the present.  It is the era in which the mammals flourished.  It began as the last dinosaurs became extinct, at the end of the Mesozoic Era.  Most of the placental mammals and all of the primates evolved during the Cenozoic.
centriole  click this icon to hear the preceding term pronounced
small, dense bodies outside of a cell nucleus that contract and become visible early in mitosis and meiosis when the nuclear membrane breaks down.  Spindle fibers eventually emanate from each centriole and connect to the centromeres of chromosomes.
centromere  click this icon to hear the preceding term pronounced
a constriction in a chromosome where two or more chromatids come together.
cerebral cortex   click this icon to hear the preceding term pronounced
the outer portion of a brain's cerebrum.  This is the area associated with coordination of sensory and motor information as well as higher thought processes.
cerebral edema  click this icon to hear the preceding term pronounced
an abnormal accumulation of fluid around the brain causing it to swell.  This potentially life threatening condition can be caused by hypoxia at high altitude.  See pulmonary edema.
cerebrum  click this icon to hear the preceding term pronounced
the two large frontal lobes at the top of the brain that make up about 85% of its weight in modern humans.  Our high level mental functions, such as speech and processing complex information, occur in the cerebrum.  The cerebral cortex, or outer surface, is deeply convoluted.  About 2/3 of the human brain surface lies within these folds.  The amount of cerebral cortex folding, and subsequently the surface area of the brain, increased as humans evolved from Homo habilis to Homo erectus and ultimately Homo sapiens.
cervix  click this icon to hear the preceding term pronounced
the neck-like opening at the lower end of the uterus that connects to the vagina.
cheek pouches
cheeks that are so elastic that they can expand to allow temporary storage of food.  This is useful when there is competition.  Old World monkey in the subfamily Cercopithecinae (macaques, baboons, etc.) have cheek pouches of this sort.
chimera  click this icon to hear the preceding term pronounced     (also spelled chimaera)
an individual who is genetically two people.  Fully chimeric individuals are usually the product of two fertilized ova fusing into a single embryo shortly after conception.
Chordata  click this icon to hear the preceding term pronounced
the phylum of animals that is characterized by elongated bilaterally symmetrical bodies.  In some phase of their life cycle, they have a notochord and gill slits or pouches. Chordates also often have a head, a tail, and a digestive system with an opening at both ends of the body. The Chordata include fish, amphibians, reptiles, birds, mammals, and 2 invertebrate subphyla (tunicates and lancelets).
chordate  click this icon to hear the preceding term pronounced
a member of the phylum Chordata.
chorion  click this icon to hear the preceding term pronounced
The membrane that develops around an embryo and contributes to the formation of the placenta.  Later, as a fetus develops, the chorion fuses with the amnion.  See chorionic villi sampling for an illustration.
chorionic villi sampling  click this icon to hear the preceding term pronounced   (or biopsy click this icon to hear the preceding term pronounced)
a diagnostic procedure for pregnant women to determine whether or not their fetuses have gross chromosomal anomalies.  It involves collecting a small sample of chorion cells for karyotyping.  The biopsy usually is done by inserting a small flexible plastic tube through the vagina and the cervix of the uterus to draw out a sample of chorion tissue.   Alternately, the cells may be extracted with a hypodermic needle through the uterine wall, as in the case of amniocentesis.   With CVS, there is approximately 98% accuracy in diagnosing Down syndrome and many other conditions due to gross chromosomal abnormalities.  However, the accuracy in predicting neural tube defects is lower than with amniocentesis.  Some sources refer to CVS as "chorionic villus sampling".  "Villus" is the singular of "villi".
chromatids  click this icon to hear the preceding term pronounced
one of two or more strands of a chromosome that are joined at a centromere.
chromosome  click this icon to hear the preceding term pronounced
a discrete, thread-like, gene-carrying body in the nucleus of a cell.  Chromosomes are composed primarily of DNA and protein.  They are visible only under magnification during certain stages of cell division.  Humans have 46 chromosomes in each somatic cell and 23 in each sex cell.
chronic disease
an illness that lasts for a long period of time or indefinitely.  In contrast, an acute disease is one with a rapid onset and a short but usually severe course.
chronometric click this icon to hear the preceding term pronounced date
a date that places an event in its chronological position with reference to a universal time scale such as a calendar.   Such dates usually are given in terms of the number of years before or after a calendar starting point.  For instance, 1950 B.C. was 1950 years before the beginning date of the Gregorian calendar, which is commonly used today.  Chronometric dating methods include the use of written records, dendrochronology, and radiometric methods.  See relative date.
cladistics  click this icon to hear the preceding term pronounced
an approach to discovering evolutionary relationships between organisms based on shared derived traits.  Cladistics has largely replaced the older approach known as evolutionary or phylogenetic sytematics which grouped organisms together based on homologies in general without distinguishing between primitive and derived ones.
cladogenesis  click this icon to hear the preceding term pronounced
the branching pattern of evolution resulting from adaptive radiation.
class
the level of classification below subphylum and above subclass in the Linnaean classification system.  Humans are members of the class Mammalia.
clavicles  click this icon to hear the preceding term pronounced
collarbones; the bones that connect the sternum with the scapula.  A single clavicle on each side of the body goes from the center of the upper chest to the shoulders.
clinal model  click this icon to hear the preceding term pronounced    (of human variation)
a system for classifying people based on the knowledge that genetically inherited traits often gradually change in frequency from one geographic region to another--that is, they change in clines.
clines  click this icon to hear the preceding term pronounced
progressively changing zones of degree difference in frequency of a trait with movement from one region to another.  The gradual decrease in frequency of the B blood allele going west in Europe is an example of such a gradation or clinal distribution.  See discontinuous distribution.
codominance  click this icon to hear the preceding term pronounced
the situation in which two different alleles for a trait are expressed unblended in the phenotype of heterozygous individuals.  Neither allele is dominant or recessive, so that both appear in the phenotype or influence it.  Type AB blood is an example.  Such traits are said to be codominant.
codon  click this icon to hear the preceding term pronounced
a sequence of three nucleotide bases in a DNA or RNA molecule that code for a specific type of amino acid that will be used in the synthesis of a protein.
collarbones
see clavicles.
color blindness
the inability to see certain colors as they normally appear to others.  The most common form of this vision deficiency is X-linked genetically inherited red-green color blindness.
conduction  click this icon to hear the preceding term pronounced
the movement of heat from one object to another by direct contact.  Example: the transmission of heat from your body to the chair on which you are sitting.  See convection and radiation.
consanguineous mating  click this icon to hear the preceding term pronounced
the mating of closely related individuals, such as brothers, sisters, or cousins.  Another name for this mating pattern is "inbreeding."  This is an extreme form of positive assortative mating.
convection  click this icon to hear the preceding term pronounced
the movement of heat from on object to the surrounding fluid (either gas or liquid).  Example: the transmission of heat from your body to water when you are swimming.  See conduction and radiation.
convergence  click this icon to hear the preceding term pronounced
the development of a similar anatomical feature in distinct species lines after divergence from a common ancestor that did not have the initial trait that led to it.  The common ancestor is usually more distant in time than is the case with parallelism.  Convergence is thought to be due primarily to the independent species lines experiencing the same kinds of natural selection pressures.  Convergence is also referred to as convergent evolution.  Convergence results in homoplasies.
convergent evolution
see convergence.
core body temperature
the temperature of the internal organs in the chest cavity, abdominal region, and head in animals.  See hyperthermia and hypothermia.
core tool  click this icon to hear the preceding term pronounced
a tool made from a relatively large block of rock rather than from the flakes that are removed from it by percussion flaking in the manufacturing process.  Most hand axes are core tools.
cosmic radiation  click this icon to hear the preceding term pronounced
streams of highly penetrating charged particles (composed of free electrons, protons, alpha particles, and a few heavier atom nuclei) that bombard the earth at high speed from outer space.  On entering our  upper atmosphere, they commonly collide with gas atoms and alter the atomic structures of those atoms.
cranial capacity
the volume displaced by the brain within a cranium click this icon to hear the preceding term pronounced, or skull case.  Cranial capacity is a simple measure of brain size but not necessarily of intelligence.
creationism  click this icon to hear the preceding term pronounced
the belief that all species were created as they are today and that they have not undergone any evolution since then.  This view is usually based primarily on the Book of Genesis in the Judeo-Christian Bible.  Most creationists also believe that the Earth is very young (typically about 6,000 years old).  In the U.S. creationism is the basis for what has become known as "creation science."
Cro-Magnon  click this icon to hear the preceding term pronounced
the modern Homo sapiens who appeared in Europe by 40,000 years ago.  Their skeletons generally were lighter than the Neandertals who occupied Europe at that time.  The Cro-Magnon had broad, small faces with pointed chins and high foreheads.  They are the ancestors of modern Europeans.
crossing-over
the exchange of genetic material (DNA) between homologous chromosomes at the beginning of meiosis.  This results in sperm and ova with greater genetic diversity due to a recombination of genes.  Specifically, a portion of the end of a chromosome is broken and reattached on another chromosome.
cross-pollination
the mating of two genetically different plants of the same species.  Usually, the term is used in reference to the crossing of two pure breeding (homozygous) plants.
crystal lattice  click this icon to hear the preceding term pronounced
the three-dimensional pattern of a crystalline solid.  There are characteristic lattice patterns identified for different minerals.
cusps  click this icon to hear the preceding term pronounced
the elevated, somewhat pointed portions of the chewing surfaces on premolar and molar teeth.
cystic fibrosis  click this icon to hear the preceding term pronounced
a genetically inherited disease in children that results in chronic fluid development in the lungs, making breathing difficult.  This disease also prevents normal absorption of fats and other nutrients from food.  Cystic fibrosis occurs as a result of inheriting a recessive allele for if from both parents.  This is ultimately a fatal disease, but with modern medical care, about 2/3 of the people with it survive into early adulthood.  About 30,000 people have cystic fibrosis in the U.S. today.
cytoplasm  click this icon to hear the preceding term pronounced
all of the material within a cell between the nuclear and cell membranes.  The cytoplasm consists of semifluid water-rich viscous gel and contains numerous specialized structures, or organelles, involved with cell function.

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- D -

demography  click this icon to hear the preceding term pronounced
the study of population characteristics, especially its size, density, and growth patterns.
dendrochronology  click this icon to hear the preceding term pronounced
the study of annual growth-rings of trees, usually for the purpose of chronometric dating logs found in association with relatively recent archaeological sites.  Tree-ring sequences also are used as records of cycles in local climates.
dental formula
the quantity of each type of tooth (e.g., incisor, canine, premolar, and molar) in each quadrant of the mouth, counting from the front.  The human dental formula is 2.1.2.3.  The Old World monkeys and apes also share this dental formula.
deoxyribonucleic acid  click this icon to hear the preceding term pronounced
see DNA.
derived trait    (in regards to classifying organs)
a biological trait that has changed over time from the ancestral form and/or function that was present in the species from which it came.  See cladistics.
descent with modification
a phrase Charles Darwin used to refer to the process by which natural selection favors some variations resulting in their becoming more common in the next generation.  Descent with modification is another way of describing evolution.
developmental acclimatization
see developmental adjunstment.
developmental adjustment
a change in the normal growth patterns and development of an individual that occurs in childhood as a result of specific cultural practices (e.g., foot binding) or other environmental processes.  The anatomical and physiological changes that result are mostly irreversible by adulthood.  Example: stunted growth and mild mental retardation due to severe, prolonged undernourishment.  Developmental adjustment is also referred to as "developmental acclimatization."
diabetes  click this icon to hear the preceding term pronounced
an inherited metabolic disorder in which there are abnormally high blood sugar levels.  In advanced stages, this often results in blindness from cataracts, nerve damage, gangrene in the feet and legs leading to amputation, heart disease, and kidney failure.  Type 1 diabetes melitis (juvenile onset diabetes) is due to decreased production of insulin by the pancreas.  Type 2 diabetes melitis is due to increased resistance of cells in the body to insulin.  The gene or genes for diabetes are incompletely penetrant.
Diego click this icon to hear the preceding term pronounced blood system
a human blood typing system in which there are 2 distinct types: Diego positive and Diego negative.  An individual inherits a Diego type from his or her parents and does not change it throughout life.  Apparently, the only people in the world who are Diego positive are some Native Americans and East Asians.
digits  click this icon to hear the preceding term pronounced
fingers and toes.  See pentadactylism.
diploid click this icon to hear the preceding term pronounced number
the full component of chromosomes normally found in somatic cells.  In humans, the number is 46.  See haploid number.
directional selection
Selection for or against one extreme of a trait.  In the case of polygenic traits that are expressed as a continuum of phenotypes, such as human stature, it would be selection for people who are either very tall or very short.  The result would be a progressive increase in the form of the trait that is being selected for and a reduction in the form that is being selected against.  In the case of a trait controlled by only two alleles, it would be selection against one of the alleles.  When that allele is recessive, it is usually selection against the recessive homozygote and for the dominant homozygote and the heterozygote.  An example is selection against people who have a fatal genetically inherited disease that only shows up in homozygous recessive people.  The result would be a progressive reduction of the recessive allele in the gene pool of the population and, subsequently, a reduction in the number of people who have the disease.  Continuous directional selection can result in evolution.  See disruptive selection and stabilizing selection.
disruptive selection
Selection for both extremes of a trait and against the middle.  In the case of polygenic traits that are expressed as a continuum of phenotypes, such as human stature, it would be selection for both very tall and very short people and against those who are average in height.  The result would be a progressive increase in both of the extreme forms of this trait and a reduction in the middle range.  In the case of a trait controlled by only two alleles, it would be selection for both recesssive and dominant homozygotes and against heterozygotes.  The result would be a progressive reduction in the number of people who are heterozygous for the trait in the population.  See directional selection and stabilizing selection.
discontinuous distribution  click this icon to hear the preceding term pronounced
the geographic distribution of a trait such that it appears in high or low frequencies in various areas with little or no gradation between them.  See clines.
display
a visual message, or body language, used by primates and other animals primarily to communicate anger, fear, and other basic emotions.  Displays are a strong indication of an animal's emotional state.  See agonistic display.
diurnal  click this icon to hear the preceding term pronounced
being awake and active during the daylight hours but sleeping during the nighttime.  See nocturnal.
DNA  click this icon to hear the preceding term pronounced   (deoxyribonucleic acid click this icon to hear the preceding term pronounced)
a large organic molecule that stores the genetic code for the synthesis of proteins.  Each chromosome consists mostly of a DNA molecule.  DNA is composed of sugars, phosphates and bases arranged in a double helix shaped molecular structure.  Segments of DNA correspond to specific genes.
dominance hierarchy  click this icon to hear the preceding term pronounced
a group of individuals arranged in rank order.  In some non-human primate species, each community has a distinct male and female dominance hierarchy.  Every individual is ranked relative to all other community members of the same gender.  In the case of rhesus macaque females, rank is determined by the relative rank of their mothers.  Depending on the species, male ranking may be similarly determined by the mother's rank or it may be earned in competition with other males.  Individuals who are higher in the dominance hierarchy usually have greater access to food, sex, and other desirable things.   See alpha male and female. 
dominant allele
an allele that masks the presence of a recessive allele in the phenotype.   Dominant alleles for a trait are usually expressed if an individual is homozygous dominant or heterozygous.
 
photo of a dog illustrating dorsal, ventral, anterior, and posterior

dorsal  click this icon to hear the preceding term pronounced

the biological sciences use the terms dorsal, ventral, anterior, and posterior to refer to direction within the body of a bilaterally symmetrical organism.  These terms are illustrated in the photo on the right.  Body parts on the sides of a body are referred to as being lateral.  If something is along the longitudinal midline of a body, it is medial.
double helix  click this icon to hear the preceding term pronounced
the twisted ladder shape that is characteristic of DNA molecules.
Down syndrome  click this icon to hear the preceding term pronounced
a genetically inherited form of mental retardation usually resulting from the inheritance of an extra autosome 21.   Down syndrome individuals also typically are short and stocky in build with short appendages.  They usually have broad round faces, saddle-shaped nose profiles, and thick tongues that are often stuck out of their mouths.  The incidence of Down syndrome children goes up rapidly with the age of the mother, particularly after 40.

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- E -

ecological niches  click this icon to hear the preceding term pronounced
specific micro-habitats in nature to which populations or organisms adapt.   They are usually seen in terms of being food getting opportunities in the environment.
ectothermic  click this icon to hear the preceding term pronounced
the ability to maintain core body temperature in a normal range mainly by avoiding exposure to environmental temperature extremes.  Reptiles, amphibians, fish, and insects are ectothermic animals.  Ectothermy is also referred to as being cold blooded.  See endothermic.
edema  click this icon to hear the preceding term pronounced
abnormal fluid retention in the tissues and/or cavities of the body resulting in swelling.
electron spin resonance click this icon to hear the preceding term pronounced dating   (ESR)
a radiometric dating method based on the fact that background radiation causes electrons to separate from their atoms and become trapped in the crystal lattice of minerals.  When odd numbers of electrons are separated, there is a measurable change in the magnetic field (or spin) of the atoms.  Since the magnetic field progressively changes with time in a predictable way as a result of this process, it provides an atomic clock, or calendar, that can be used for dating purposes.  This technique is employed primarily to chronometrically date calcium carbonate in limestone, coral, teeth, mollusks, and egg shells.  It can also date quartz and flint.
Ellis-van Creveld syndrome  click this icon to hear the preceding term pronounced
a genetically inherited disorder characterized by dwarfism, extra fingers, and malformations of the arms, wrists, and heart.  The majority of the known cases in the world of this rare syndrome have been found among the Amish and 7% of them carry the responsible recessive autosomal allele.
embryo  click this icon to hear the preceding term pronounced
the earliest stage of development of an unborn child.  In humans, the embryonic stage lasts up till about the 8th week of pregnancy.   Following, is the fetal stage.
embryonic  click this icon to hear the preceding term pronounced
see embryo.
endemic click this icon to hear the preceding term pronounced disease
a disease that remains at a more or less constant frequency of affected individuals in a population all of the time.  Examples: hypertension, tooth decay, and malaria.
endoplasmic reticula  click this icon to hear the preceding term pronounced   (singular, endoplasmic reticulum click this icon to hear the preceding term pronounced)
highly folded long membrane structures in the cytoplasm of cells.  Ribosomes involved in protein synthesis are on the surface of these bodies.
endothermic  click this icon to hear the preceding term pronounced
the ability to maintain a relatively constant core body temperature regardless of external conditions by using internal physiological means.  That is to say, they are homeothermic, or stable in core body temperature, as a result of endothermy.  Birds and mammals are endothermic.   Endothermy is also referred to as being warm blooded.  See ectothermic.
enzyme  click this icon to hear the preceding term pronounced
a type of protein that causes or regulates specific chemical reactions within cells.
Eocene Epoch  click this icon to hear the preceding term pronounced
the second geological epoch of the Cenozoic Era.  The Eocene spanned the time approximately 55.8-33.9 million years ago.
epicanthic fold  click this icon to hear the preceding term pronounced
a fold of skin over the inner corner of each eyelid.  This is characteristic of normal East Asians (see photo on right).  It is also typical of people with Down syndrome from any population in the world.  The presence of epicanthic folds does not imply Down's.
epidermis  click this icon to hear the preceding term pronounced
the outer most skin layer in humans and related animals.
erythroblastosis fetalis  click this icon to hear the preceding term pronounced
a blood disease of fetuses and newborn infants caused by the mother's anti-Rh+ antibodies agglutinating or bursting the red cells of her infant's Rh+ blood.  Symptoms include life threatening anemia,  jaundice, fever, swollen tissues from edema, and an enlarged liver and spleen.  Serious cases are treated by blood replacement.  Erythroblastosis fetalis is also referred to as "hemolytic anemia" and "hydrops fetalis."
erythrocytes  click this icon to hear the preceding term pronounced
the relatively large red cells in blood that transport oxygen from the lungs to all of the living tissues of the body.  Normally, 40-45% of human blood volume consists of erythrocytes.  See stem cells.
estrogen  click this icon to hear the preceding term pronounced
a class of feminizing hormones.   Both men and women produce them, but females normally produce much more.
estrus  click this icon to hear the preceding term pronounced
the period of time when female animals are sexually excited and receptive to mating.  Estrus occurs around the time of ovulation in many species.
ethnocentrism  click this icon to hear the preceding term pronounced
the feeling that your own group's cultural traditions and values are correct and superior to all others.  This is usually coupled with a generalized dislike and even contempt for people who have other cultural traditions.   Ethnocentrism is universal in that all people around the world are ethnocentric to some degree.
eukaryotic click this icon to hear the preceding term pronounced cell
a cell that has a true nucleus and that divides by mitosis.  Complex single celled creatures such as protozoa as well as all multicelled plants and animals are primarily eukaryotes.  With the exception of red blood cells, human cells are eukaryotic.  See prokaryotic cell.
eumelanin  click this icon to hear the preceding term pronounced
See melanin.
Eurasia  click this icon to hear the preceding term pronounced
the combined land mass of Europe and Asia.
Eutheria  click this icon to hear the preceding term pronounced
the infraclass of therian mammal species in which females produce a placenta to connect the fetus to the uterus.  This enables nutrients and oxygen to get to the fetus and provides a means of eliminating waste products.  As a result, eutherian mammals can carry their young within the uterus until late in fetal development.  This has a selective advantage because it results in decreased infant mortality.  Eutherian mammals are also called placental mammals.  Included in this infraclass are dogs, cats, bears, whales, monkeys, humans, and many other mammals.
evaporative cooling
cooling of the skin resulting from the evaporation of sweat on its surface.  In hot dry environments, this is normally the most significant mechanism by which the human body loses excess heat.
evolution  click this icon to hear the preceding term pronounced
genetic change in a population of organisms that occurs over time.  The term is also frequently used to refer to the appearance of a new species.  More specifically, it is change in the frequencies of alleles in a population's gene pool from one generation to the next.
exons  click this icon to hear the preceding term pronounced
DNA base pairs that code for proteins and, therefore, are part of genes.  Only 1.2-1.5% of DNA consists of exons.  See introns.

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- F - 

f1 generation  click this icon to hear the preceding term pronounced
the first offspring (or filial) generation.   The next and subsequent generations are referred to as f2, f3, etc.
false positive
a test result that indicates a medical problem when there actually is not one.
femur  click this icon to hear the preceding term pronounced
the scientific name of the upper leg bones.  In the case of 4 legged animals, the femurs are in the rear legs.
fertilization
conception; the process of sexual reproduction by which the chromosomes from a sperm cell enter the nucleus of an ovum and combine with its chromosomes to create a zygote.
fetal position  click this icon to hear the preceding term pronounced
laying partly curled on one's side with the legs and arms bent and held into the body. 
fetus  click this icon to hear the preceding term pronounced
an unborn child during the later stages of pregnancy.  In humans, an embryo usually becomes a fetus after the 8th week of gestation.  Unlike embryos, fetuses have clearly recognizable physical characteristics of the species and gender.
first cousin
someone who is related as a result of being a child of one's uncle or aunt.
fission track click this icon to hear the preceding term pronounced dating
a radiometric dating method based on the fact that when trace amounts of uranium-238 fission there is a release of highly energy-charged alpha particles which burn narrow fission tracks, or damage trails, through glassy materials such as obsidian (i.e., volcanic glass), mica, and zircon crystals.  The number of fission tracks is directly proportional to the time since the material cooled from a molten state.  The rate at which fission tracks occur is related to the half-life of uranium-238, which is approximately 4.5 billion years.
flake tool  click this icon to hear the preceding term pronounced
an artifact made from a flake knocked off of a larger rock usually by percussion flaking.  See core tool.
flint  click this icon to hear the preceding term pronounced
a kind of hard, rock with a glassy opaque appearance.  It was a favorite raw material for many prehistoric humans for the manufacture of tools such as knives and scraping implements.
flora and fauna  click this icon to hear the preceding term pronounced
terms of Latin origin that are commonly used in the sciences to refer to the plants (flora) and animals (fauna) in an environment.
fluorine click this icon to hear the preceding term pronounced analysis dating
a relative dating method based on the fact that bones buried in the ground progressively lose nitrogen and gain fluorine and other trace elements.  The rate at which these changes occur depends on the local environment.  If two bones from the same site have markedly different amounts of nitrogen and fluorine, it is a strong indication that they did not come from the same time period.  The bone with the least amount of nitrogen and the greatest amount of fluorine is most likely the oldest.
foraging group
a group of animals that seek food together.  In the case of non-human primates, this group may consist of all community members or only some of them.
foramen magnum  click this icon to hear the preceding term pronounced
the hole at the base of a skull through which the spinal cord passes.  Literally, foramen magnum means a "large hole or opening" in Latin.  The position of the foramen magnum is a strong indicator of the angle of the spinal column to the head and subsequently whether the body is habitually horizontal (like a horse) or vertical (like a monkey).  
fossil  click this icon to hear the preceding term pronounced
any remains or traces of ancient organisms.  Often fossils are mineralized bone, though they have also been found in the form of casts, molds, animal tracks, frozen or desiccated bodies, and creatures trapped in amber.
founder principle
a small population size effect in which the genes of a few people (the population founders) are inherited over time by a large number of descendents.  This is also known as the "founder effect" and the "Sewall Wright effect."  See genetic drift.
fragile-X syndrome  click this icon to hear the preceding term pronounced
a relatively common genetically inherited abnormality of the X chromosome which results in mental retardation.  Since it is an X-linked trait, males more often have it expressed in their phenotypes.   Most fragile-X males have large testes, big ears, narrow faces, and sensory integration dysfunctions that result in learning disabilities.  It is likely to occur 1 in 1000 births.  Approximately 1 in 700 females are carriers of the gene for this trait.
free-ranging population
a non-captive group of primates or other animals that is living in its natural habitat, largely free from constraints imposed by humans.
frequency
the number of times that something happens.  For example, the number of people out of 100 who get divorced would be the frequency of divorce.
frontal     (in reference to a skull)
the forehead region of the head.

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- G -

gamete  click this icon to hear the preceding term pronounced
a reproductive cell--sperm or unfertilized ovum cell produced in the testes and ovaries of animals.  Gametes are produced by meiosis.  They normally have half the number of chromosomes found in somatic cells.
gastrointestinal  click this icon to hear the preceding term pronounced
relating to the stomach and the intestines--the lower digestive tract.

gene flow

the transference of genes from one population to another, usually as a result of migration.  The loss or addition of individuals can easily change the gene pool frequencies of both the recipient and donor populations--that is, they can evolve.

gene pool

the sum of all of the alleles of genes in all of the individuals in a population.
gene  click this icon to hear the preceding term pronounced
a unit of inheritance usually occurring at a specific location, or loci, on a chromosome.  Physically, a gene is a sequence of DNA bases that specify the order of amino acids in a protein or, in some cases, a small RNA molecule referred to as a microRNA.  A gene may be made up of hundreds to thousands of DNA bases.  Genes are responsible for hereditary characteristics.
genera  click this icon to hear the preceding term pronounced
see genus.
genetic bottlenecking
see bottleneck effect.

genetic drift

evolution, or change in gene pool frequencies, resulting from random chance.  Genetic drift occurs most rapidly in small populations.  In large populations, random deviations in allele frequencies in one direction are more likely to be cancelled out by random changes in the opposite direction.
genetic equilibrium
the situation in which a population is not evolving from generation to generation--that is, the population's gene pool frequencies remain unchanged.
genetics  click this icon to hear the preceding term pronounced
the study of gene structure and action and the patterns of inheritance of traits from parent to offspring.  Genetic mechanisms are the underlying foundation for evolutionary change.  Genetics is the branch of science that deals with the inheritance of biological characteristics. 
genetic load
a measure of all of the harmful recessive alleles in a population or family line.  A high genetic load would be one in which there is a high frequency of deleterious recessive alleles.
genome  click this icon to hear the preceding term pronounced
the full genetic complement of an individual (or a species).  In humans, it is estimated that each individual possesses approximately 3 billion nucleotides in all of the DNA that makes up his or her genome.  See Human Genome Project. 

genome imprinting  click this icon to hear the preceding term pronounced

an inheritance pattern in which a gene will have a different effect depending on the gender of the parent from whom it is inherited.  Genome imprinting is also known as genetic imprinting.
genotype  click this icon to hear the preceding term pronounced
the genetic makeup of an individual.  Genotype can refer to an organism's entire genetic makeup or the alleles at a particular locus.  See phenotype.
genus  click this icon to hear the preceding term pronounced   (plural genera click this icon to hear the preceding term pronounced)
a group of closely related species.  In the Linnaean classification system, genus is the category immediately above species.
geochronology  click this icon to hear the preceding term pronounced
a relative dating method based on the association of early human sites with changing features of the land, such as the advance and retreat of glaciers or the rise and fall of sea levels.  When these events are well dated, geochronology could be considered a reliable calibrated relative dating technique.  Associated evidence may be changes in the frequency of plant species measured by pollen count and other kinds of paleoecology evidence.
geological unconformities  click this icon to hear the preceding term pronounced
breaks in the original stratigraphic sequence of a geological deposit.   Understanding all of the unconformities in an area is a prerequisite for using stratigraphy for relative dating purposes.
geomagnetic polarity time scale  click this icon to hear the preceding term pronounced   (GPTS)
See paleomagnetic dating.
geomagnetic reversal time scale  click this icon to hear the preceding term pronounced   (GRTS)
See paleomagnetic dating.
gestation  click this icon to hear the preceding term pronounced
the period between conception and birth during which an unborn young is within its mother's uterus.  Pregnancy is another word for gestation.
gills  click this icon to hear the preceding term pronounced
breathing organs used to extract oxygen from water.
glacial   click this icon to hear the preceding term pronounced
A long period of time during which earth's climate cools, causing glaciers to expand out from the poles and mountains covering vast areas.  The glacials of the Pleistocene Epoch mostly occurred in the northern hemisphere.  See interglacial.
Gloger's Rule  click this icon to hear the preceding term pronounced
within the same species of warm-blooded animals, there is a tendency for darker, more heavily pigmented skin to occur in animals near the equator and lighter pigmented skin farther from it.  This is because of the selective advantage the coloration provides.  Heavy pigmentation protects from skin cancer caused by ultraviolet radiation from the sun.  However, too much pigmentation can significantly reduce the skin's ability to produce vitamin D, which is necessary for the absorption of calcium and phosphorus from food.  Open country close to the equator typically experiences high amounts of intense ultraviolet radiation while temperate and arctic regions have relatively little.  Subsequently, heavy skin pigmentation is an advantage near the equator but a disadvantage farther away from it.  Gloger's Rule was named after Wilhelm Gloger, a 19th century naturalist. 
gracile  click this icon to hear the preceding term pronounced
graceful, slender, and delicate.   This 17th century English term is used to describe the body characteristics (especially bones) of the early australopithecines and the earliest humans.
gradualism  click this icon to hear the preceding term pronounced
see phyletic gradualism.

great chain of being

the theory that living things were divinely created and exist in an infinite and continuous series of forms, each one grading into the next, from simple to complex.  This view goes back to the ancient Greeks and was popular from the Middle Ages through the 18th century in Europe.
Great Rift Valley  click this icon to hear the preceding term pronounced
 long depression in Southwest Asia and East Africa caused by the movement of tectonic plates, largely beginning during the Oligocene Epoch.  In Africa, it extends from Ethiopia southwest 1200 miles through the lake regions.  Many of the early hominin discovery sites are in this valley system.

glucose-6-phosphate dehydrogenase deficiency  click this icon to hear the preceding term pronounced     (G6PD deficiency )

a genetically inherited X-linked error in metabolism caused by an inadequate amount of the enzyme glucose-6-phosphate dehydrogenase in red blood cells.  When exposed to certain environmental influences, such as fava beans and some drugs (sulphonamide antibiotics, some antimalarials including primaquine, and several other sulphur-containing drugs) , the red cells of individuals with this deficiency burst, resulting in severe anemia.   As in the case of sickle-cell trait and thalassemia, this anemia may provide some immunity to falciparum malaria.  G6PD deficiency is also known as "favism."  It is the most common type of human enzyme deficiency--about 400 million people have this condition around the world.   It is a common problem especially in populations around the Mediterranean Basin, the Middle East, and Southeast Asia.

great apes

the gorillas, common chimpanzees, and bonobos of Africa and the orangutans of Southeast Asia.  These species are referred to as great apes because they are the largest apes.  See lesser apes.
Gregorian click this icon to hear the preceding term pronounced calendar
the most commonly used calendar system in the world today.  It is based on the older Julian calendar of the late Roman Empire but more accurately corresponds to the solar year of 365.2422 days.  The Julian calendar year is 365.25 days.  This is inaccurate by approximately 11 minutes a year.  The result is that the Julian calendar is out of sync by one day every 131 years.  The Gregorian calendar fixed this problem by changing the rules for leap years.  In the Julian system, a day is added to the end of February every 4 years.  In the Gregorian system a year is a leap year if it is divisible by 4 unless it is divisible by 100 but not by 400.  This eliminates leap years periodically in order to keep the calendar more synchronized with the solar year.  The Gregorian calendar was named after Pope Gregory XIII who officially approved it in 1582 A.D.  England and its colonies did not adopt it until 1752.
grooming
carefully picking through hair looking for insects, twigs, and other debris.  See allogrooming and autogrooming.

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half-life
the amount of time for half of the atoms of a radioactive element in a sample to decay, or fission.  The reduction in the number of atoms follows a geometric scale--at the end of 2 half-lives, there are 1/4 of the atoms left; at the end of 3 half-lives, there are 1/8 remaining; etc.
hand ax
a rock core or large flake that has been systematically worked by percussion flaking to an elongated oval biface shape with one pointed end and sharp edges on the sides.  In profile, hand axes usually have a teardrop or leaf shape.  Hand axes are diagnostic tools of the Acheulian tool tradition of Homo erectus after about 1.5 million years ago.  They continued to be made and used by early archaic humans.  Very likely, they were multipurpose implements used for light chopping of wood, digging up roots and bulbs, butchering animals, and cracking bones.  
haploid click this icon to hear the preceding term pronounced number
the number of chromosomes in gametes.  Human sperm and ova normally contain only 23 chromosomes, which is the result of the halving of chromosome pairs in meiosis.  See diploid number.
Hardy-Weinberg equilibrium click this icon to hear the preceding term pronounced equation
the equation (p²+2pq+q² = 1) used by population geneticists to determine probable genotype frequencies of a population for specific traits.  By comparing these frequencies for subsequent generations, it is possible to track the direction and rate of evolution.
hematite  click this icon to hear the preceding term pronounced
a rust red iron ore that was ground to a powder state and used as a paint pigment, beginning with the Neandertals and early modern humans.
hemizygous click this icon to hear the preceding term pronounced chromosomes
The X and Y chromosomes of males are mostly not homologous--they only share a few genes.  Those genes that are found on only the X or the Y chromosome are said to be hemizygous because there is only one copy of each gene.  Regardless of whether that gene is a dominant or a recessive allele, it will be expressed in the phenotype of males.
hemoglobin  click this icon to hear the preceding term pronounced
the gas transporting protein molecule that normally makes up 95% of the volume of red cells in blood.  There are usually about 270,000,000 hemoglobin molecules in each red cell.
hemophilia  click this icon to hear the preceding term pronounced
an X-linked genetically inherited recessive disease in which one or more of the normal blood clotting factors is not produced.  This results in prolonged bleeding from even minor cuts and injuries.  Swollen joints caused by internal bleeding are a common problem for hemophiliacs.  Hemophilia most often afflicts males.
herbivorous  click this icon to hear the preceding term pronounced
eating only vegetable foods.  Animals that have this sort of diet are herbivores or vegetarians. See carnivorous and omnivorous.
hermaphrodite  click this icon to hear the preceding term pronounced     (now more commonly referred to as "intersex")
an individual who has one or more testes and ovaries and whose external genitalia are not clearly male or female.  This condition can occur in chimeras who have inherited both a male and a female set of sex chromosomes.  True hermaphrodites have one testes and one ovary.  Male pseudohermaphrodites, or "merms," have testes but no ovaries and display some female genitalia tissue.  Female pseudohermaphrodites, or "ferms," have ovaries but no testes and display some male genitalia tissue.
heterodont  click this icon to hear the preceding term pronounced
animals that have a variety of specialized teeth (incisors, canines, premolars, and molars).  Mammals are heterodonts.
heterosis  click this icon to hear the preceding term pronounced
increased health of individuals who are the result of negative assortative mating, or crossbreeding.  This is due to the fact that when mates are from very different genetic lines they are more likely to have lower frequencies of homozygous recessive conditions.  Subsequently, they are liable to be more viable.  This phenomenon has also been referred to as hybrid vigor.
heterozygous  click this icon to hear the preceding term pronounced
a genotype consisting of two different alleles of a gene for a particular trait (Aa).   Individuals who are heterozygous for a trait are referred to as heterozygotes.   See homozygous.
hierarchical  click this icon to hear the preceding term pronounced
an arrangement in terms of rank or importance.  The Linnaean classification system of living things is hierarchical--it is a system of classification with the highest category consisting of all living things.   Lower down are levels of less inclusive sub-categories.  The lowest sub-category is a species. 

HIV  click this icon to hear the preceding term pronounced   (Human Immunodeficiency Virus)

the virus that is responsible for causing AIDS.
HLA  system  click this icon to hear the preceding term pronounced
referring to the over 100 antigens on the surface of human body tissue cells that can be recognized by some kinds of leukocytes and potentially lead to the rejection of these tissues if they are alien.  The HLA system has the most genes of any other known human multiple-allele series.  There are at least 30,000,000 possible HLA genotypes.   When organ transplants fail, it is usually due to HLA incompatibility.  This can be prevented by making sure that the donor and the recipient have the same or very similar HLA types.  Immunosuppressant drugs also are now available to restrain the HLA system and thereby allow successful transplants when there is an HLA incompatibility between donor and recipient.  HLA stands for "human leukocyte antigen" click this icon to hear the preceding term pronounced. 
homeotic gene  click this icon to hear the preceding term pronounced
see regulator gene.
hominid  click this icon to hear the preceding term pronounced
any species of the primate family Hominidae click this icon to hear the preceding term pronounced.  The great apes and humans are the only hominids today, however, there were other species in the past.
hominin   click this icon to hear the preceding term pronounced
any species of the primate tribe Hominini.   The australopithecines and humans are hominins
hominini   click this icon to hear the preceding term pronounced
see hominin.
hominoid  click this icon to hear the preceding term pronounced
any species of the primate superfamily Hominoidea click this icon to hear the preceding term pronounced.  All hominids and apes are hominoids.
Homo  click this icon to hear the preceding term pronounced
the genus in which all humans are classified. 
Homo erectus  click this icon to hear the preceding term pronounced
the species of humans that followed Homo habilis and preceded Homo sapiens in our line of evolution.  Homo erectus evolved in East Africa by 1.8 million years ago.  They were the first humans to expand their range into Asia and Europe.  By at least 400,000 years ago or even earlier in some areas, they were beginning a transitional evolutionary phase that would eventually lead to archaic humans.  See Homo ergaster and Homo heidelbergensis.
Homo ergaster  click this icon to hear the preceding term pronounced
An early form of the species Homo erectus from East Africa.  In an alternate interpretation, some researchers consider Homo ergaster to be the species that immediately preceded Homo erectus in our line of evolution.  Homo ergaster fossils date about 1.8-1.5 million years ago.
Homo habilis  click this icon to hear the preceding term pronounced
a transitional species between the australopithecines and Homo erectus.  Homo habilis appeared by 2.4 million years ago and continued until about 1.6 million years ago.  They lived in East and possibly South Africa.
Homo heidelbergensis  click this icon to hear the preceding term pronounced
A very early form of archaic humans in Europe and North Africa that lived from about 800,000 to 200,000 years ago.  In an alternate interpretation, some researchers consider Homo heidelbergensis to be a separate species or even a late advanced Homo erectus in transition to archaic humans.  Homo heidelbergensis may have been the ancestor of the Neandertals.
Homo neanderthalensis  click this icon to hear the preceding term pronounced
the species designation given to the Neandertals by researchers who believe that these ancient people were different enough from Homo sapiens to assign them to a distinct species.
Homo rudolfensis  click this icon to hear the preceding term pronounced
An early form of the species Homo habilis.  In an alternate interpretation, some researchers consider Homo rudolfensis to be the species that immediately preceded Homo habilis in our line of evolution.  Homo rudolfensis fossils date 2.4-1.6 million years ago.
Homo sapiens sapiens  click this icon to hear the preceding term pronounced
See Homo sapiens.
Homo sapiens  click this icon to hear the preceding term pronounced
the genus (Homo) and species (sapiens) categories to which modern humans belong.  Homo sapiens evolved from Homo erectus over several hundred thousand years beginning at least 400,000 years ago.  The first modern Homo sapiens evolved from archaic humans by about 130,000 years ago in Africa.  Modern humans are referred to as Homo sapiens sapiens.  The last sapiens refers to our sub-species or variety designation.
Homo sapiens neanderthalensis  click this icon to hear the preceding term pronounced
the species designation given to the Neandertals by researchers who believe that these ancient people were genetically close enough to Homo sapiens to assign them to the same species but a different sub-species or variety.  See Homo neanderthalensis.
homologies  click this icon to hear the preceding term pronounced
anatomical structures in different species that are similar due to descent from a common ancestor that had them.  Homologies are also referred to as homologous structures or features.  see cladistics.
homologous chromosomes  click this icon to hear the preceding term pronounced
chromosomes that are paired during meiosis.  Such chromosomes are alike with regard to size and also position of the centromere.  They also have the same genes, but not necessarily the same alleles, at the same locus or location.  All autosomes and the sex chromosomes of females occur in homologous pairs.  The sex chromosomes of males are mostly hemizygous.
homologous structures  click this icon to hear the preceding term pronounced
see homologies.
homoplasies  click this icon to hear the preceding term pronounced
similar anatomical structures in different species that were not present in their common ancestor.  Homoplasies are also referred to as homoplastic structures or features.  Homoplasies can be due to parallelism, convergence, or even chance.
homoplastic structures  pronounce word
see homoplasies.
homozygous  click this icon to hear the preceding term pronounced
having the same allele at the same locus on both members of a pair of homologous chromosomes.  Homozygous also refers to a genotype consisting of two identical alleles of a gene for a particular trait.  An individual may be homozygous dominant (AA) or homozygous recessive (aa).  Individuals who are homozygous for a trait are referred to as homozygotes.  See heterozygous.
hormone  click this icon to hear the preceding term pronounced
a class of substances (usually proteins) that are produced by specialized cells and that travel to other parts of the body, where they influence chemical reactions and regulate various cellular functions.  Hormones include the secretions of the endocrine glands that affect metabolism and behavior.  Testosterone, estrogen, and insulin are examples of such hormones.
human
a member of the genus Homo.
Human Genome Project
a multinational research effort designed to identify and map the location of all human genes.  The idea of a Human Genome Project began at a 1984 international conference in Utah.  Research to decode the human genome began in earnest in 1986, funded by the U.S. Department of Energy.  The initial stage of discovering all human DNA codons was completed early in 2001 at a cost of 2.7 billion dollars.  The next phase of research will be to identify the proteins for which these genes code.  This decoding of the human proteome will be an even more daunting task than the original Human Genome Project.  See genome.
Huntington's disease
a severe genetically inherited fatal degenerative nerve disorder.  The symptoms usually do not appear until early middle age.  There is a progressive loss of muscle control that inevitably leads to paralysis and death.  This disease is also called Huntington's chorea click this icon to hear the preceding term pronounced. 
hybrid  click this icon to hear the preceding term pronounced
an offspring that is the result of mating between two genetically different kinds of parents--the opposite of purebred.
hybrid vigor
see heterosis.
hyoid bone  click this icon to hear the preceding term pronounced
a horseshoe-shaped bone in the neck above the larynx supporting the base of the tongue.  Since jaw, tongue, and larnyx muscles are anchored to it, the hyoid bone is essential for the production of sounds used in human speech.  Humans are the only primates that have their hyoid bones high in the neck.  Subsequently, they can produce a wider range of vocal sounds than other primates.
hyperthermia  click this icon to hear the preceding term pronounced
unusually elevated core body temperature resulting from fever or prolonged exposure to a hot environment.   This can be a life threatening condition.  See hypothermia.
hypothalamus  click this icon to hear the preceding term pronounced
a small region near the base of the brain that controls the sympathetic nervous system, which in turn regulates the autonomic functions of the body, including beating of the heart, breathing, and body temperature control.
hypothermia  click this icon to hear the preceding term pronounced
unusually low core body temperature resulting from prolonged exposure to a cold environment.  This can be a life threatening condition.  See hyperthermia.
hypoxia  click this icon to hear the preceding term pronounced
oxygen deprivation. This condition can occur at high altitude.  Symptoms include a reduced ability to do work, fatigue, dizziness, nausea, and an inability to effectively perform memory intensive tasks.  Even moderate hypoxia results in the death of some individuals due to heart failure.  In very high mountain areas, hypoxia can cause pulmonary edema and/or cerebral edema, both of which are life-threatening conditions that are aspects of what is often referred to as acute mountain sickness.

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- I -

imitative magic
See sympathetic magic.
immunization  click this icon to hear the preceding term pronounced
the development of antibodies to antigens that are alien to your body.  Immunity can be developed to blood and tissue types as well as microorganism parasites (e.g., bacteria and viruses).
incomplete penetrance
the situation in which an allele is expressed only if certain factors are present in the environment.  The triggering of genetically inherited diabetes by obesity and possibly severe emotional stress is an example.
inbreeding
see consanguineous mating.
inbreeding depression
The reduction in viability and subsequent loss of reproductive potential of purebred varieties.  This is a consequence of a pattern of consanguineous mating that goes on for many generations in a family line or a small inbred population.
incisors  click this icon to hear the preceding term pronounced
chisel shaped teeth at the front of the mouth in mammals.  All primates normally have 8 incisors (2 in each quadrant of the mouth).  The common mammal pattern is 12 incisors (3 in each quadrant).  See dental formula.
index fossil
remains of a plant or animal of a species that is known to have lived only during a specific time period.  The discovery of such a fossil in an archaeological site is circumstantial evidence of the approximate time period that it was occupied.  Fossil bones of horse and elephant related species are often used to relatively date fossils of our ancestors.  Index fossils are used for biostratigraphy.
inheritance of acquired characteristics
Lamarck's theory that evolution occurs as a result of an organism acquiring a change in form due to using or not using particular body parts during its lifetime and then passing the new trait on to its offspring.  This is also referred to as the "use-disuse theory."
Insectivore  click this icon to hear the preceding term pronounced
animals in the mammalian order Insectivora.  They were named for their adaptation to eating insects. The insectivores were among the earliest of the placental mammals to evolve.
interglacial  click this icon to hear the preceding term pronounced
A long period of warmer conditions between glacials when the earth's glaciers have shrunk to a smaller area.  Interglacials during the Pleistocene Epoch lasted 10's of thousands of years.  We are probably in an interglacial at present.
intermediate expression
the situation in which a heterozygous genotype results in a phenotype that is intermediate between those resulting from the homozygous genotypes.  The mid-range baritone male voice is an example.
Intersex
see hermaphrodite.

introns  click this icon to hear the preceding term pronounced

sections of DNA molecules that do not code for proteins but still perform important functions.  Apparently, some are enhancers or suppressors of genes.  About a fourth of DNA consists of introns.  The remaining "junk" DNA, that makes up three fourths of a DNA molecule, very likely also has subtle functions.  For instance, It helps determine the shape of chromosomes and also buffers against change by absorbing the mutagenic click this icon to hear the preceding term pronounced effect of radiation and viruses.  See exons.
invertebrate  click this icon to hear the preceding term pronounced
an animal that lacks an internal skeleton.  All animals other than fish, amphibians, reptiles, birds, and mammals are invertebrates.  Approximately 95% of all animals are invertebrates. 

in vitro fertilization  click this icon to hear the preceding term pronounced    (IVF)

a set of medical procedures to help a couple have children if they have not been able to in the past due to low sperm count, blocked fallopian tubes, and some other causes of infertility.  The woman is given fertility inducing drugs to cause her to ovulate numerous ova which are surgically removed and fertilized outside of her body with sperm from her mate or another donor.  Two or more of the fertilized ova are then placed into her uterus in the hope that one or more will attach and develop into viable embryos.  As a result, multiple births are relatively common with IVF.

ischial callosities  click this icon to hear the preceding term pronounced

hairless, callused areas on either side of the rump of monkeys in the Old World monkey subfamily Cercopithecinae (macaques, baboons, etc.) and the small apes of Asia. 
isotope  click this icon to hear the preceding term pronounced
any of two or more forms of an element that differ in terms of atomic mass but have the same atomic number--for example, carbon-12, carbon-13, and carbon-14 are all isotopes of carbon.

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jaundice  click this icon to hear the preceding term pronounced
the condition in which the eyes, skin, and/or urine become unusually yellowish as a result of the build up of bilirubin in the blood.

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- K -

karyotype  click this icon to hear the preceding term pronounced
a standardized arrangement of pictures of an individual’s chromosomes cut out from a microphotograph of a cell and rearranged into homologous pairs according to size and other physical characteristics.  The standardized arrangement of karyotypes allows medical researchers to discover if an individual is a male or female and if he/she has any gross chromosomal abnormalities.
kinship  click this icon to hear the preceding term pronounced
relationships that are recognized between individuals based on family ties.  Among humans, those ties are created by marriage and shared descent from ancestors.  Among non-human primates, they are due to descent.
Klinefelter syndrome  click this icon to hear the preceding term pronounced
a genetically inherited sex chromosome abnormality only affecting males.  Genotypically, they are XXY or more rarely  XXXY, or XXXXY.  They have asexual to feminine body contours as well as breast enlargement and relatively little body hair.  They are sterile or nearly so and their penis, testes, and prostate gland are small.  Like metafemales, most Klinefelter syndrome men are an inch or so above average height.  They usually have slight learning difficulties, especially with language.  However, most are sufficiently ordinary in appearance and mental ability to live in society without notice.  The frequency of Klinefelter syndrome has been reported to be between 1 in 500 and 1 in 1,000 male births.   Males with Down syndrome sometimes also inherit Klinefelter syndrome.
knuckle walking
the form of four legged locomotion used by gorillas and chimps.  They walk on the soles of their feet but not on the palms of their hands.  They bend their fingers and support the head end of their bodies with their knuckles instead of their open palms.
kwashiorkor  click this icon to hear the preceding term pronounced
the disease of babies and very young children resulting from long-term severe protein deficiency in the diet.  There is usually an associated deficiency in the consumption of vitamin A and E as well as zinc and selenium.  Symptoms include edema (or swelling) due to water retention (especially in the abdomen), stick-like legs and arms with little fat or muscle mass, apathy, and loss of hair and skin pigmentation in patches.  As in the case of marasmus, children with kwashiorkor are likely to have their growth retarded.  Kwashiorkor usually results from a child being weaned too early and being forced to subsist mainly on a high carbohydrate and low protein diet.

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lactase  click this icon to hear the preceding term pronounced
an enzyme produced by mammals to break down lactose in milk that they consume.  Lactase is needed for the digestion of uncooked dairy products.  Lactase deficiency results in diarrhea and other symptoms of physical intolerance of most dairy products.
lactose  click this icon to hear the preceding term pronounced
a sugar normally present in milk.  Lactose intolerance is often due to lactase deficiency.  However, physical intolerance of dairy products can also result from an allergy to milk proteins.
lateral  click this icon to hear the preceding term pronounced
see dorsal.
lesser apes
the gibbons and siamangs of Southeast Asia.   These species are referred to as lesser apes because they are the smallest apes. See great apes.
leukemia  click this icon to hear the preceding term pronounced
a class of cancers of the blood cells and blood-forming organs resulting in exceptionally high leukocyte (white blood cell) production.  Other organs can become involved as well.  Leukemia can be caused by some viruses, chemicals, and radiation.  However, there also may be a genetic connection.  For instance, individuals with Down syndrome have a much higher chance of developing leukemia.
leukocytes  click this icon to hear the preceding term pronounced
the so-called white cells in blood.  They exist in variable numbers and types but make up a very small part of human blood volume.  Some leukocytes (i.e., lymphocytes pronounce word) provide a physiological defense against infection.  As a result, their numbers increase when the body is under attack by bacteria and viruses.  Some other types of leukocytes (i.e., macrophages click this icon to hear the preceding term pronounced)  have the function of getting rid of old unneeded blood cells.  See stem cells.
Levallois click this icon to hear the preceding term pronounced flake
flakes of more or less standardized shapes and sizes made with a specific technique in the Mousterian tool tradition of the Neandertals and some of their contemporaries.  Flint and other brittle fracturing rock cores were percussion flaked on one side until a convex "tortoise shell" shape was formed.  Then, a heavy percussion blow at one end of the core removed a large flake that was convex on one side and relatively flat on the other.  This was a Levallois flake. 
linked genes
genes that are on the same chromosome and subsequently are inherited together as a package unless crossing-over separates them.
Linnaean click this icon to hear the preceding term pronounced classification system
referring to the classification system in use by the biological sciences today to classify all living things.  It lumps organisms together based on presumed homologies.  The assumption is that the more homologies two organisms share, the closer they must be in terms of evolutionary distance.  The higher, more inclusive divisions of the Linnaean system are created by including together closely related clusters of the immediately lower divisions.  The result is a hierarchical system of classification with the highest category consisting of all living things.  The lowest category consists of a single species.  Each of the categories above species can have numerous subcategories.   The Linnaean system was invented by Carolus Linnaeus pronounce name in the 18th century.
lipids  click this icon to hear the preceding term pronounced
a class of organic molecules that include fats, oils, and waxes.
locomotor patterns  click this icon to hear the preceding term pronounced
the methods an animal uses to move.  These may include such things as swimming, jumping, walking, brachiating, etc.
locus  click this icon to hear the preceding term pronounced   (plural, loci click this icon to hear the preceding term pronounced )
the position on a chromosome where a given gene occurs.  The term is sometimes used interchangeably with gene, but this usage is technically incorrect.
Lower Paleolithic
the earliest and longest part of the Paleolithic click this icon to hear the preceding term pronounced stage of development.  The Lower Paleolithic began with the Oldowan tool tradition of Homo habilis and continued with the Acheulian tradition of Homo erectus and early archaic humans.  The Lower Paleolithic began about 2.5-2.4 million years ago and continued until after 100,000 years ago.  Lower Paleolithic tool making was the height of technology for most of the time that we have been human.

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- M -

macroevolution  click this icon to hear the preceding term pronounced
major evolutionary changes in a population's gene pool, occurring over many generations, resulting in the evolution of new species.  See microevolution.
macroscopic  click this icon to hear the preceding term pronounced
referring to objects that are large enough to be seen easily with the naked eye.
malaria  click this icon to hear the preceding term pronounced
a group of similar life threatening diseases found mostly in tropical and subtropical regions of the world.  Malaria is caused by any of four different microorganisms called plasmodia (Plasmodium falciparum, vivax, ovale, and malariae).  These single-celled organisms are transmitted from person to person mostly by anopheles mosquitoes as they extract blood.  Symptoms of malaria include chills, high fever, and sometimes fatal irregularities of the brain, liver, kidney, and/or blood.  There are at least 100,000,000 new cases of malaria reported annually around the world.  Approximately 1,500,000 people die from it each year (mostly children--3,000 children die of malaria every day).
malnourishment  click this icon to hear the preceding term pronounced
an inadequacy or an excess of some key element(s) in the diet, such as proteins, fats, or specific minerals and vitamins.  See undernourishment and overnourishment
mammal  click this icon to hear the preceding term pronounced
an animal in the class Mammalia.
Mammalia  click this icon to hear the preceding term pronounced
a class of warm blooded, usually hairy animals, that feed their young with milk secreted by the mammary glands of females.  Mammalia include monotremes, marsupials, primates, cats, dogs, bears, hoofed animals, rodents, bats, seals, dolphins, and whales. 

mammary glands  click this icon to hear the preceding term pronounced

milk secreting glands of mammals.   They are usually located on the chest or abdomen in one or more bilaterally symmetrical pairs.  Mammary glands are also referred to as breasts.
manual dexterity  click this icon to hear the preceding term pronounced
referring to the ability to manipulate objects with the hands.
marasmus  click this icon to hear the preceding term pronounced
the medical condition resulting from prolonged famine.  Symptoms include extreme emaciation, diarrhea, anemia, and apathy.  Women with marasmus usually stop ovulating.  The loss of insulating body fat makes people with marasmus highly vulnerable to death resulting from a drop in core body temperature when the air falls below 60-65° F.  Children who survive marasmus usually develop short adult stature and some degree of permanent brain damage.  See kwashiorkor.
marsupial  click this icon to hear the preceding term pronounced
see Metatheria.
matrilineal descent  click this icon to hear the preceding term pronounced
recognizing family ties only between mothers and their children.
medial  click this icon to hear the preceding term pronounced
see dorsal.
medical syndrome
see syndrome.
meiosis  click this icon to hear the preceding term pronounced
the cell division process in specialized tissues of female ovaries and male testes which results in the production of sex cells, or gametes.  Meiosis involves two divisions and produces four sperm cells in males and one ovum in females from a starting cell.  Each sperm and ovum contains only half the original number of chromosomes--23 in the case of humans.  Subsequently, meiosis is also called "reduction division."  Spermatogenesis is the term used for meiosis in males and  oögenesis refers to the same process in females.  See mitosis.  
Melanesia  click this icon to hear the preceding term pronounced
New Guinea and other nearby islands in the Southwest Pacific Ocean. Indigenous people from this region are referred to as Melanesians.
melanin  click this icon to hear the preceding term pronounced
a dark colored organic pigment produced in the skin.  There are two forms of melanin----pheomelanin, which is red to yellow in color, and eumelanin, which is dark brown to black.  People with light complexioned skin mostly produce pheomelanin, while those with dark colored skin mostly produce eumelanin.   High concentrations of melanin near the surface of the skin result in a darker complexion.   Suntanned skin also has higher concentrations of melanin.
melanocytes  click this icon to hear the preceding term pronounced
specialized cells that produce melanin in the skin.
melanoma  click this icon to hear the preceding term pronounced
A type of aggressive skin cancer.  Specifically, it is a cancer that begins in melanocytes and rapidly spreads to other parts of the body.
Mendelian genetics  click this icon to hear the preceding term pronounced
inheritance patterns which can be explained by simple rules of dominance and recessiveness of genes.
Mesozoic Era  click this icon to hear the preceding term pronounced
the geological era immediately preceding the Cenozoic Era and dating approximately 251-65.5 million years ago.  The Mesozoic was the era in which the dinosaurs flourished and the first mammals and birds evolved.
messenger RNA   (mRNA)
the form of RNA that carries a copy of a specific sequence of genetic information (a gene) from the DNA in the cell nucleus to the ribosomes in the cytoplasm where it is translated in order to synthesize a protein.  Messenger RNA is assembled on one strand, or side, of a DNA molecule.
metabolism  click this icon to hear the preceding term pronounced
the chemical and physical processes continuously going on in the cells of living organisms.  These are the processes by which energy and matter are made available for use by the cells of an organism.  Heat is a byproduct of metabolism.
metafemale  click this icon to hear the preceding term pronounced
a genetically inherited sex chromosome abnormality only affecting females.  Metafemales inherit three X chromosomes--their genotype is XXX.  As adults, these individuals are usually an inch or so taller than average with unusually long legs and slender torsos.  They have normal development of sexual characteristics and are fertile.  They may have slight learning difficulties and are usually in the low range of normal intelligence.  They tend to be emotionally immature for their size during childhood.  None of these traits prevent them from being socially accepted as ordinary women.  This type of chromosomal abnormality is apparently rare and little is known about it.  However, the frequency is approximately 1 in 1,000 female infants and it may be more common when the mother is older.  Metafemales are also called "triple-X females."
Metatheria  click this icon to hear the preceding term pronounced
the infraclass of therian mammal species in which females bear their young in an immature condition (while still in the early fetal stage) and then permit their further infant development in an abdominal pouch covering their mammary glands.  Compared to the delayed births of placental mammals, this is inefficient in keeping young infants alive.  Metatherian mammals are also called marsupials.  Included in this infraclass are kangaroos, koalas, opossums, etc.
microcephaly  click this icon to hear the preceding term pronounced
an extremely rare genetically inherited condition in which babies are born with extremely small brains and heads.  This fatal condition has been found only among the children of 23 Old Order Amish families in Lancaster County Pennsylvania.
microevolution  click this icon to hear the preceding term pronounced
small changes in a population's gene pool occurring over a few generations.  The accumulation of microevolutionary changes can result in macroevolution.
micro RNA   (miRNA)
a very short form of RNA in the nucleus of cells.  Micro RNA molecules are typically only 20-25 base units long.  They are transcribed from DNA, but are not involved directly in protein synthesis like other forms of RNA. They perform important functions similar to enzymes in regulating chemical reactions in our cells, especially in the embryonic stage at the beginning of life.  It is thought that 1/3 or more of human genes are controlled in some way by micro RNA molecules.  At least 200-255 human DNA genes code for the production of micro RNA molecules.
midden  click this icon to hear the preceding term pronounced
an archaeological term referring to composted soil resulting from a refuse heap left by humans in the past.  Middens often contain artifacts and food refuse remains such as bone and mollusk shell fragments. 
Middle Paleolithic
the part of the Paleolithic click this icon to hear the preceding term pronounced stage of development in which the Mousterian tool tradition of the Neandertals and early modern humans was used.  The Middle Paleolithic began about 75,000 years ago and continued until at least 28,000 years ago.
minerals  click this icon to hear the preceding term pronounced
inorganic, naturally occurring materials consisting of specific elements.  They are usually rocks with a characteristic crystalline structure and other identifiable physical traits.  Quartz, talc, and ordinary table salt are examples of minerals.
Miocene Epoch  click this icon to hear the preceding term pronounced   
the fourth geological epoch of the Cenozoic Era.  The Miocene occurred approximately 23-5.3 million years ago.
mitochondria  click this icon to hear the preceding term pronounced   (singular, mitochondrion click this icon to hear the preceding term pronounced)
small rod-like structures in the cytoplasm that produce fuel for the cell in the form of adenosine triphosphate (ATP).  A small amount of DNA in a circular looping chromosome is located in mitochondria.  This DNA is normally inherited only from mothers and is distinct from DNA that makes up the chromosomes within the cell nucleus.
mitochondrial DNA  click this icon to hear the preceding term pronounced   (mtDNA)
DNA located in the mitochondria.  Since it is normally inherited only from mothers, an offspring's mtDNA will be identical to its mother's, unless a mutation has occurred.
Mitochondrial Eve  click this icon to hear the preceding term pronounced
The name given by advocates of the replacement model of modern Homo sapiens to the last presumed common ancestor of modern humans based on a comparison of mitochondrial DNA from around the world.  She is presumed to have lived about 200,000 years ago
mitosis  click this icon to hear the preceding term pronounced
the simple cell division process that occurs in somatic cells.  One cell divides into two offspring cells that are identical to each other in their chromosome complement.  Mitosis produces cells with diploid numbers of chromosomes--46 in the case of humans.   See meiosis.
modifying gene
a gene that can alter the expression of another gene in the phenotype of an individual.
molar click this icon to hear the preceding term pronounced teeth
the comparatively large grinding teeth at the back of the mouth in mammals.  In hominids and all other anthropoids, there are normally 3 molars in each quadrant of the mouth.  See premolar and canine teeth.
Mongoloidism  click this icon to hear the preceding term pronounced
a now rejected alternate term for Down Syndrome.
monogamous  click this icon to hear the preceding term pronounced
having only one mate at a time.  Monogamy is rare among nonhuman primates but common among humans.
monosomy  click this icon to hear the preceding term pronounced
the form of aneuploidy in which there is only one chromosome instead of the usual two homologous chromosomes of each type.  Conceptions with autosomal monosomies die before birth.
monotremes  click this icon to hear the preceding term pronounced
see Prototheria.
monozygotic twins  click this icon to hear the preceding term pronounced
identical twins.  Twins that come from the same zygote and are, subsequently, the same genetically in terms of their nuclear DNA.  Any differences between monozygotic twins later in life are mostly the result of environmental influences rather than genetic inheritance.  Fraternal twins may look similar but are not genetically identical.  Monozygotic twins may not share all of the same sequences of mitochondrial DNA.  This is due to the fact that the mitochondria in a cell may have somewhat different versions of DNA, and the mitochondria can be dispersed unequally when a zygote fissions.  Female monozygotic twins can also differ because of differences between them in X-chromosome inactivation.  Subsequently, one female twin can have an X-linked condition such as muscular dystrophy and the other twin can be free of it.
morphology  click this icon to hear the preceding term pronounced
the physical form or structure of an organism or another object.   Species are usually identified from the fossil record based on morphological traits.
morphospecies  click this icon to hear the preceding term pronounced
a species that has been defined on the basis of physical, measurable characteristics.  See biospecies.
mosaicism  click this icon to hear the preceding term pronounced   (or mosaic click this icon to hear the preceding term pronounced pattern of genetic inheritance)
a genetic pattern in which an individual has two distinct cell groupings--one with normal cells and another with a genetic problem.  For instance, some people with Down syndrome produce both normal somatic cells and cells with an extra
mosaic pattern of evolution
a pattern of evolution in which different parts of the body evolve at different rates.  In the case of humans, we essentially attained our modern form below the neck by at least 2 million years ago.  However, our cranial capacity did not reach its current size until after 100,000 years ago.
mother-fetus incompatibility  click this icon to hear the preceding term pronounced
the situation in which a mother's blood type is different from that of her unborn child.  In the case of some combinations of types, the mother's blood system can produce antibodies to antigens on the surface of the red cells of her fetus resulting in their agglutination.  This is the case when the mother is Rh- and her fetus is Rh+.  As a result of this incompatibility, the fetus can develop erythroblastosis fetalis.
Mousterian click this icon to hear the preceding term pronounced tool tradition
the most advanced tool making tradition of the Neandertals.  It was also shared by some other late archaic humans and early modern Homo sapiens.  The Mousterian tradition was characterized by a progressive decrease in emphasis on core tools and a corresponding increase in the importance of flake tools--especially those made with the Levallois technique.  The Mousterian tradition was sufficiently advanced over the earlier Acheulian Tradition from which it was derived to be placed into the Middle Paleolithic.
multiple-allele series  click this icon to hear the preceding term pronounced
a situation in which a gene has more than two alleles.  The ABO blood type system is an example.  Multiple-allele series only partly follow simple Mendelian genetics.
multiple sclerosis  click this icon to hear the preceding term pronounced    (MS)
a genetically inherited progressive disease of the central nervous system.  MS occurs as a consequence of one's own immune system attacking the insulating sheath that normally protects neurons.  Symptoms range from numbness and tingling to paralysis.  There is a loss of motor and cognitive functions.  The gene(s) responsible for MS are incompletely penetrant in that the onset of the disease is apparently triggered by a virus and possibly other environmental factors.  There is a correlation between the amount of sunlight that children are exposed to and the likelihood that they will develop MS later in life.  People who spend much of their first 16 years in tropical and subtropical regions of the world are much less likely to develop this disease than those who live in far northern and far southern regions of our planet.  It is believed that the lack of abundant sun exposure early in life is somehow responsible for the later onset of MS.
muscular dystrophy  click this icon to hear the preceding term pronounced   (MD)
any of a group of inherited progressive muscle disorders caused by a defect in one or more genes that control muscle function.   MD is characterized by a gradual, irreversible wasting of skeletal muscle.  It is a sex-linked trait most often passed on to sons by their mothers.  The most common form, Duchene MD, begins to weaken the legs of boys by age 3 and inevitably gets worse with each passing year.  There is no cure for this disorder, and it usually results in death before the age of 30.
mutagen  click this icon to hear the preceding term pronounced
an agent that can cause a mutation to occur.  Various kinds of chemicals, viruses, and radiation have been identified as mutagens.
mutation  click this icon to hear the preceding term pronounced
an alteration of genetic material such that a new variation is produced.  For instance, a trait that has only one allele (A) can mutate to a new form (a).  A mutation can be a change in DNA bases or changes in chromosome number and /or structure.  Mutation is the only mechanism of evolution that can produce new alleles of a gene.  See mutagen.

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- N -

natural selection
an evolutionary mechanism that occurs when some individuals of a population are better able to adapt to their environment and, subsequently, produce more offspring.  Nature, in effect, selects which members of a population are fit to survive long enough to reproduce.  Differential reproductive success among individuals is the key.  Those who produce more offspring have a greater influence on the gene frequencies of the next generation.  This mechanism of evolutionary change was first described by Charles Darwin.
Neandertals  click this icon to hear the preceding term pronounced
the most well known late archaic humans.  They lived mostly in Europe and the Near East from 150,000 years ago or even earlier until at sometime after 28,000 years ago.  There is an on-going debate as to whether they should be considered Homo sapiens or a distinct but related species.  If they were members of our species, they were a different variety or race (Homo sapiens neanderthalensis).  On the other hand, if they were different enough to be a distinct species, they should be considered to be Homo neanderthalensis.
negative assortative mating  click this icon to hear the preceding term pronounced
a form of non-random mating in which individuals who are not genetically alike for particular traits mate and those who are alike do not.  The result is a progressive increase in the frequency of heterozygotes and a decrease in the homozygotes for the discriminated traits.  See positive assortative mating and random mating.
Negroid  click this icon to hear the preceding term pronounced
a presumed human "race" consisting mostly of sub-Saharan Africans.  This classification is based on the discredited typological model.  The term "Negroid" was derived from the Latin word for the color black.
neural tube defects  click this icon to hear the preceding term pronounced
defective developments of the brain or spinal cord.  By the mid embryonic stage (5 weeks in humans), a neural tube extends from the top of the head to the lower end of the spinal column.  Later, this tube becomes the brain and spinal chord.  Spina bifida and anencephaly are examples of neural tube defects.
neurotransmitters  click this icon to hear the preceding term pronounced
specialized proteins that relay, amplify and modulate electrical signals between neurons in the brain and nervous system.
New World
The New World is the Americas.  The Old World is Europe, Asia, and Africa.  This distinction is an ethnocentric reflection of the European origin of our modern sciences.
niches
see ecological niches.
nocturnal  click this icon to hear the preceding term pronounced
being awake and active when it is dark but sleeping during the day.  See diurnal.
nondisjunction errors  click this icon to hear the preceding term pronounced
a mechanical error that can occur during meiosis and mitosis.   Specifically, members of a pair of homologous chromosomes move to the same pole rather than opposite poles.  In meiosis, this can result in one gamete receiving two of the same type of chromosome and another receiving none of this type.  Nondisjunction is a cause of gross chromosomal abnormalities.
non-random mating  click this icon to hear the preceding term pronounced
mate selection based on one or more traits that are discriminated for or against.  This is a mechanism of evolution.  See positive assortative, negative assortative, and random mating.
notochord  click this icon to hear the preceding term pronounced
a rudimentary internal skeleton made of stiff cartilage that runs lengthwise under the dorsal surface of the body of chordates.  Generally, there is a single hollow nerve chord on top of the notochord.  Among humans and the other vertebrates, the notochord is replaced by a more complex skeleton following the embryonic stage of development.
nuclear family  click this icon to hear the preceding term pronounced
an adult male and female mating pair along with their children.
nuclear membrane  click this icon to hear the preceding term pronounced
the selectively permeable membrane enclosing the nucleus of a cell.
nucleic acids  click this icon to hear the preceding term pronounced
the largest of the molecules in living organisms.  It is composed of a chain of nucleotides that code for the synthesis of specific proteins.  DNA and RNA are types of nucleic acid.
nucleotide  click this icon to hear the preceding term pronounced
the basic building block of nucleic acid.   It consists of any one of four specific purine or pyrimidine bases attached to a ribose or deoxyribose sugar and phosphate group.
nucleus  click this icon to hear the preceding term pronounced
a comparatively large structure found in all eukaryotic cells.   It contains the chromosomes (nuclear DNA) and is enclosed by a nuclear membrane.

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- O -

obsidian hydration click this icon to hear the preceding term pronounced dating
potentially, a chronometric dating method based on the fact that obsidian, or volcanic glass, progressively develops a thin chemically altered outer layer due to the absorption of water.  The thickness of this hydration layer is directly proportional to the amount of time since the rock was formed or since a fresh surface was exposed to the elements.  Since the rate of hydration varies between samples from different volcanic sources, this technique could arguably be considered relative rather than chronometric.
Oldowan click this icon to hear the preceding term pronounced tool tradition
the earliest stone tool making tradition.  The first Oldowan artifacts were made in East Africa about 2.5-2.4 million years ago presumably by Homo habilis and continued to be made by early Homo erectus until about 1.5 million years ago.  They consisted of simple core and flake tools only slightly modified from their natural state by percussion flaking.
Old Stone Age
see Paleolithic.
Old World
The Old World is Europe, Asia, and Africa.  The New World is the Americas.  This distinction is an ethnocentric reflection of the European origin of our modern sciences.
olfactory  click this icon to hear the preceding term pronounced
the sense of smell.  With the exception of prosimians, primates are relatively poor at olfactory sensing.
Oligocene Epoch  click this icon to hear the preceding term pronounced
the third geological epoch of the Cenozoic Era.  The Oligocene occurred approximately 33.9-23 million years ago.
omnivorous  click this icon to hear the preceding term pronounced
the ability to live by eating both meat and vegetable foods.   See carnivorous and herbivorous.
oöcyte  click this icon to hear the preceding term pronounced
an immature female sex cell.  These egg precursor cells, or primary oöcytes, are produced before birth.  They become secondary oöcytes usually one by one after puberty when hormones trigger ovulation.
oögenesis  click this icon to hear the preceding term pronounced
the meiosis process of female sex cells that produces ova.  It takes place mostly in the ovaries of humans and other female animals.
optically stimulated luminescence (OSL) dating
a comparatively new radiometric dating technique similar to thermal luminescence.  OSL is based on the fact that minerals in sediment grains are affected by prolonged exposure to light.  Specifically, light causes electrons of the mineral atoms to be progressively dislodged.  This provides a natural clock.  So far, the OSL technique has been used to date silty or sandy water deposited sediments that are 1/2 million years old or younger.
order
a Linnaean classification category above the level of species and genus and below class.  Each order can consist of many species and genera.
organelle  click this icon to hear the preceding term pronounced
a general term referring to any of the discrete structures within a cell that perform specific functions (e.g., mitochondria).
osmosis  click this icon to hear the preceding term pronounced
diffusion of a liquid through a membrane.
Osteodontokeratic click this icon to hear the preceding term pronounced tool tradition
a hypothetical early human and possibly late australopithecine tool making tradition based on the use of bones, teeth, and horns.  This was proposed in the 1940's by Raymond Dart, but most paleoanthropologists reject it today.
osteoporosis  click this icon to hear the preceding term pronounced
a bone disorder in which there is a progressive reduction in bone density resulting in brittleness and increased porosity.    People with osteoporosis are at a high risk for bone fractures.  This disorder is most commonly found among post-menopausal women.  However, it also occurs at a high frequency among men who have low testosterone levels  (e.g., men with Klinefelter syndrome).
over expression
the abnormal expression of a trait in the phenotype of an individual resulting from the presence of extra chromosomes or copies of the genes responsible for the trait.  For example, Down syndrome traits are likely the consequence of inheriting three chromosome 21's instead of the usual two.  Apparently, the genes on the extra chromosome are also expressed. 
overnourishment  click this icon to hear the preceding term pronounced
regular consumption of too many calories.  Prolonged over nourishment can result in chronic obesity, which is associated with higher risks for type 2 diabetes, heart disease, and some kinds of cancer.   See malnourishment.
ovulation  click this icon to hear the preceding term pronounced
the release of a secondary oöcyte from an ovary to begin its path down a fallopian tube (or oviduct) to the uterus.
ovum  click this icon to hear the preceding term pronounced   (plural, ova click this icon to hear the preceding term pronounced)
a female sex cell or gamete that has completed all of the phases of the meiosis process.
oxidizable carbon ratio (OCR) dating
an experimental dating technique based on the fact that organic carbon in soil humus and charcoal progressively convert to oxidizable carbon over time.  The ratios of these two forms of carbon vary directly with the age of the material.  This technique requires an inexpensive chemical analysis procedure.  The effective time range for OCR dating has not yet been established.

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- P -

paleoanthropology  click this icon to hear the preceding term pronounced
the study of the fossil and archaeological record of humans and their primate ancestors.  It is also known as "human paleontology."
Paleocene Epoch  click this icon to hear the preceding term pronounced
The first geological epoch of the Cenozoic Era.  The Paleocene occurred approximately 65.5-55.8 million years ago.
paleoecology  click this icon to hear the preceding term pronounced
the study of ancient environments.  See geochronology and palynology.
Paleolithic  click this icon to hear the preceding term pronounced
the earliest stone tool making traditions from the first ones made by Homo habilis down to the most advanced ones of the last Ice Age made by modern Homo sapiens.  Paleolithic literally means "Old Stone" Age.  See Lower, Middle, and Upper Paleolithic.
paleomagnetic click this icon to hear the preceding term pronounced dating
dating methods based on the fact that the magnetic north pole wanders around the rotational north pole and has repeatedly reversed position with the magnetic south pole at irregular intervals in the past.  There are permanent records of these movements in the form of thermoremanent magnetism found in burned clay and rock as well as geological deposits of volcanic origin.  Archaeomagnetic dating is the term generally used for dating based on the wandering of the magnetic north pole around the rotational north pole over the last 10,000 years or so.  Geomagnetic reversal time scale click this icon to hear the preceding term pronounced (GRTS) dating and geomagnetic polarity time scale click this icon to hear the preceding term pronounced (GPTS) dating are terms applied to the method based on the much longer term reversals of the magnetic poles.  The two related paleomagnetic dating methods have been considered by some researchers to be chronometric and calibrated relative by others.
paleontology  click this icon to hear the preceding term pronounced
the study of earlier forms of life present in the fossil record.   See paleoanthropology.
paleospecies  click this icon to hear the preceding term pronounced
a group of similar fossils considered to be members of the same species because the range of their morphological variation does not exceed the range of variation of a living species.  See species.
palynology  click this icon to hear the preceding term pronounced
the study of plant pollen, usually for the purpose of reconstructing ancient climates and dating soil strata.  Palynology is an important tool of paleoecology.
pangenesis  click this icon to hear the preceding term pronounced
Charles Darwin's incorrect theory about the inheritance of traits.  He proposed that hereditary particles in the body are affected by the things an individual does during his or her lifetime.  These modified particles were thought to migrate via blood to the reproductive cells and subsequently could be inherited by the next generation.  This was a variation of Lamarck's incorrect idea of the "inheritance of acquired characteristics."
parallel evolution
see parallelism.
parallelism  click this icon to hear the preceding term pronounced
a similar evolutionary development in different species lines after divergence from a common ancestor that had the initial anatomical feature that led to it.  Parallelism is thought to be due primarily to the independent species lines experiencing the same kinds of natural selection pressures.    Parallelism is also referred to as parallel evolution.  Parallelism results in homoplasies.  See convergence.
paranthropoids  click this icon to hear the preceding term pronounced
members of the hominin genus Paranthropus click this icon to hear the preceding term pronounced described first in the 1930's by Robert Broom.  Since the 1960's, most paleoanthropologists have not classified them as a separate genus but, rather, as members of the genus Australopithecus.  From this perspective, the paranthropoids were the robust australopithecines.  They lived during the late Pliocene and early Pleistocene geological Epochs in Africa (i.e., ca. 2.5-1.4 million years ago). .
partial replacement model
See assimilation model.
pathology  click this icon to hear the preceding term pronounced
the study of conditions, processes, or results of diseases.  Pathology also is used to refer to any abnormal physiological condition.
Peking Man  click this icon to hear the preceding term pronounced
See Sinanthropus pekinensis.
pelvis  click this icon to hear the preceding term pronounced
the bowl-shaped ring of bones in the hip region at the base of the torso, supporting the spinal column and resting on the legs.  It is also referred to as the pelvic girdle.
pentadactylism   click this icon to hear the preceding term pronounced
having five digits on the end of feet and hands.  This trait is characteristic of all primates except for the spider monkey which has five toes on each foot but only four fingers on each hand.  Pentadactylism is an ancient mammalian trait that was inherited from their reptile ancestors.
percussion flaking  click this icon to hear the preceding term pronounced
a tool making technique in which a brittle rock (e.g., obsidian, flint, chert, and basalt) that will potentially be an artifact is struck with a heavy glancing blow from another dense rock (i.e., a hammerstone) in order to cause a flake to be removed.  An artifact can be shaped by carefully and systematically directing the percussion blows with the hammerstone.  Percussion flaking works when a sufficiently large shock wave is directed into the target rock so that the elastic limit of the material is exceeded.  This causes one or more flakes to be broken off.  See pressure flaking.
peripheral blood flow
blood flowing in vessels near the surface of the skin.
peripheral vision  click this icon to hear the preceding term pronounced
the field of view outside of the line of direct site.   Primates and most other binocular animals only see two dimensions (2-D) peripherally since these are areas beyond their overlapping field of view.  See stereoscopic vision.
permafrost  click this icon to hear the preceding term pronounced
permanently frozen soil.  This is a common condition above the Arctic Circle and in other similarly cold environments.
pheomelanin  click this icon to hear the preceding term pronounced
See melanin.
phenotype  click this icon to hear the preceding term pronounced
the observable or detectable characteristics of an individual organism--the detectable expression of a genotype.
pheromones  click this icon to hear the preceding term pronounced
chemicals produced and secreted by an animal that can have a powerful affect on the behavior and development of other animals (usually in the same species).  Pheromones are common throughout the animal world, including humans.
photosynthesis  click this icon to hear the preceding term pronounced
the process by which plants, algae, and some bacteria use energy from sun light to create new organic molecules (specifically carbohydrates) out of carbon dioxide, water, and elemental nutrients in specialized chlorophyll-containing cells.  Most forms of photosynthesis produce oxygen as a byproduct.
phyletic gradualism  click this icon to hear the preceding term pronounced
a theoretical model of evolution in which species change slowly at a more or less constant rate through time into other species.  See punctuated equilibrium.
phylum  click this icon to hear the preceding term pronounced
the level of classification just below kingdom in the Linnaean Classification system.  At this level, animals are grouped together based on similarities in basic body plan or organization.
physiological plasticity  click this icon to hear the preceding term pronounced
referring to the physical moldability of an organism as it is developing.  This flexibility allows environmental forces to alter the genetically predetermined shape of our bodies to some extent.  Example: permanent changes in the shape and position of foot bones resulting from the old Chinese practice of binding, or tightly wrapping, the feet of girls.
physiology  click this icon to hear the preceding term pronounced
referring to the organic or bodily processes of an organism.   See anatomy.
Pithecanthropus erectus  click this icon to hear the preceding term pronounced
the original name given by Eugene Dubois to the Homo erectus skeletal remains from Java.  Literally, Pithecanthropus erectus means "ape-man who stands erect."  This scientific designation is no longer in use.
placenta  click this icon to hear the preceding term pronounced
an organ in the uterus of a mammal that develops from the chorion of an embryo during gestation.  The placenta is connected to an unborn child by the umbilical cord.  The placenta provides oxygen, nutrients, and antibodies for a fetus.  Following birth the placenta and umbilical cord are naturally expelled from the uterus as the "after birth." 
placental mammal  click this icon to hear the preceding term pronounced
see Eutheria
plasma  click this icon to hear the preceding term pronounced
the relatively clear liquid medium in blood which carries the red cells, white cells, and platelets.  Most of blood's volume is made up of plasma.  As the heart pumps blood to cells throughout the body, the plasma brings them nourishment and removes the waste products of metabolism.  Plasma also contains salts, sugars, lipids, amino acids, hormones, and blood clotting substances. 
platelets  click this icon to hear the preceding term pronounced
see thrombocytes.
plate tectonics
see tectonics.
pleiotropy  click this icon to hear the preceding term pronounced
the situation in which a single gene is responsible for a variety of traits.  The collective group of symptoms known as sickle-cell trait is an example.
Pleistocene Epoch  click this icon to hear the preceding term pronounced
the sixth geological epoch of the Cenozoic Era.  The Pleistocene occurred approximately 1.81 million to 10,000 years ago.  This was mostly a time of world cooling punctuated by 3-4 major ice ages.  Most human evolution took place during the Pleistocene.
point mutation
a mutation that occurs as an error in a codon of a DNA or RNA molecule.
pollen  click this icon to hear the preceding term pronounced
the male sex spores of flowering plants.  Pollen particles are usually nearly invisible, except in large concentrations, due to their extremely small size.  They can survive for hundreds of thousands of years in silty, anaerobic soils, such as mud sediments at the bottom of a lake.  When excavated from early human sites, they can be used to reconstruct what the climate was like at the time of the occupations as well as relatively date them.
polyandrous  click this icon to hear the preceding term pronounced
a mating pattern in which one female has more than one male mate.  Polyandry is rare among nonhuman primates.  It is seen only among marmosets and tamarins.   Polyandry occurs in some human societies in isolated rural regions of India, Sri Lanka, and especially Nepal, and Tibet.
polygenic trait  click this icon to hear the preceding term pronounced
an inherited trait that is determined by genes at two or more loci.  Simple Mendelian rules of dominance do not apply to the complex interaction of these genes.  As a result, phenotypes may appear as apparent blends or intermediate expressions.  Human skin and hair color are polygenic traits.  Many polygenic traits are also influenced by environmental factors.
polygynous  click this icon to hear the preceding term pronounced
a mating pattern in which one male has more than one female mate.  Polygyny is common among primates.  It is found among hamadryas baboons, geladas, langurs, howler monkeys, gorillas and many human societies.  It has been a culturally preferred marriage pattern in numerous Native American, African, and South Asian cultures.  However, polygyny is not as common among humans as monogamy, even in cultures that advocate it.
polymorphism  click this icon to hear the preceding term pronounced
a genetic trait controlled by more than one allele, each of which has a frequency of 1% or greater in the population gene pool.  See balanced polymorphism.
polyploidy  click this icon to hear the preceding term pronounced
a chromosomal abnormality in which there are extra complete multiples of chromosome sets (e.g., 23 + 23 + 23).   Polyploids are rare among animals but common in plants.  A mosaic polyploidy (with only some ployploid cells) is the common animal form.  See aneuploidy.
population
a more or less distinct group of individuals within a species who are reproductively isolated from other groups.  In other words, they restrict their mate selection to members of their own population.  This is usually due to geographic and/or social barriers to mating with outsiders.  Members of a completely isolated small population tend to have similar genetic characteristics due to generations of inbreeding.
populational viewpoint   (of classifying species from fossils)
the idea that if two fossils have major similarities they should be categorized as being members of the same species.  From this perspective, minor anatomical differences within the same population are expected since the members of living species have individual variation.  People who advocate this viewpoint are also referred to in the biological sciences and "lumpers".  See typological viewpoint.
population genetics
the study of biological inheritance patterns and changing gene pool frequencies in populations largely through the determination of allele frequencies.  Population geneticists also identify processes resulting in evolution.  See synthetic theory of evolution.
populational model   (of human variation)
a system for classifying people based on the assumption that the only biologically distinct groups are long isolated breeding populations whose evolutionary paths have separated from other populations.  Since physical and cultural barriers to interbreeding between most groups have broken down to some extent, this approach is of marginal value in grasping the reality of human variation today.
positive assortative mating  click this icon to hear the preceding term pronounced
a form of non-random mating in which individuals who are alike for particular traits mate and those who are not alike do not.  The result is a progressive increase in the frequency of homozygotes and a decrease in the heterozygotes for the discriminated traits.  See negative assortative mating, consanguineous mating, and random mating.
posterior  click this icon to hear the preceding term pronounced
see dorsal.
postmenopausal  click this icon to hear the preceding term pronounced
after the period in a woman's life when her ovulations and menstruations have reduced in frequency and finally stopped altogether--i.e., after menopause.  Menopause usually takes place between the ages of 45 and 55.
potassium-argon click this icon to hear the preceding term pronounced dating   (K-Ar)
a radiometric dating method based on the fact that potassium-40 in volcanic rock decays into argon-40 and calcium-40 at a known rate.  The half-life of potassium-40 is approximately 1.3 billion years.  Chronometric dates are determined by measuring the amount of argon-40 in a sample.  Similarly, argon-40 and argon-39 ratios can be used for chronometric dating.
prehensile  click this icon to hear the preceding term pronounced
the ability to physically grasp something.  All primates have prehensile hands.  With the exception of humans, they all also have effective prehensile feet.  The larger New World monkeys (Cebidae) have prehensile tails as well.  Some marsupials living in the eastern islands of Indonesia and New Guinea also have this characteristic.
premolar click this icon to hear the preceding term pronounced teeth
the teeth with two-pointed crowns located between the molars and the canines.   In hominins, apes, and all Old World monkeys, there are two premolars in each quadrant of the mouth.  The premolars are also called bicuspids click this icon to hear the preceding term pronounced.
prepared core
a rock core that has been preliminarily shaped by rough percussion flaking in order to remove flakes of standardized sizes and shapes.  See punch flaking and Levallois flake.
pressure flaking  click this icon to hear the preceding term pronounced
a tool making technique developed in the Upper Paleolithic as a further refinement in shaping brittle-flaking rock artifacts .  After preliminary shaping by percussion flaking, they often finished a tool with pressure flaking.  They used a hard pointed object, like the tip of a deer antler, to literally push off flakes in the final shaping and thinning process.  This resulted in small, regular flake scars and much greater control in determining the shape of the final product.  Pressure flaking was also used to retouch, or sharpen, sharp edges.
primary context
referring to the position in a site where an object was originally deposited.  Finding an artifact or fossil in primary context allows a researcher to apply the principle of association in dating and interpreting it.  This cannot be done if the object is in a secondary context, which is to say that it was moved to a new location after the original deposition.
primary oöcyte
see oöcyte.
Primates  click this icon to hear the preceding term pronounced
the biological order that includes all humans, apes, monkeys, and prosimians, and closely related animals.
primatology  click this icon to hear the preceding term pronounced
the study of primates and their behavioral patterns.  Primatologists usually carry out long term field studies of free-ranging populations.
primitive trait    (in regards to classifying organs)
a biological trait that has not changed over time from the ancestral form and/or function that was present in the species from which it came.  See cladistics.
principle of association
the assumption that if two objects are found in their primary context in the same strata of a site, they very likely date to the same time period.
principle of independent assortment
Gregor Mendel's second principle of genetic inheritance.   It states that different pairs of genes are passed to offspring independently so that new combinations of genes, present in neither parent, are possible.  In other words, the distribution of one pair of alleles does not influence the distribution of another pair.  The genes controlling different traits are inherited independently of one another.
principle of segregation
Gregor Mendel's first principle of genetic inheritance.  It states that, for any particular trait, the pair of genes of each parent separate (during the formation of sex cells) and only one gene from each parent passes on to an offspring.  In other words, genes occur in pairs (because chromosomes occur in pairs).  During gamete production, the members of each gene pair separate, so that each gamete contains one member of each pair.  During fertilization, the full number of chromosomes is restored, and members of gene pairs are reunited.
principle of superposition  click this icon to hear the preceding term pronounced
the assumption that if there are layers in a sedimentary deposit, those laid down first will be on the bottom and those laid down last will be on the top.  This is the basis of using stratigraphy as a relative dating method.
prion  click this icon to hear the preceding term pronounced
a protein that has the ability to cause the cells that it invades to repeatedly duplicate it.  Prions are responsible for causing Mad Cow Disease.  Apparently, prions are not effectively attacked by their host's immune system nor can they be killed with existing antibiotics, extreme heat, cold, or other normally lethal conditions.  The word prion comes from "proteinaceous infectious particle."
probability
the likelihood that a specific event will occur.   Probability is usually expressed as the ratio of the number of actual occurrences to the number of possible occurrences.
prokaryotic click this icon to hear the preceding term pronounced cell
a cell that lacks a true nucleus and divides by simple fission rather than mitosis.  Bacteria and blue-green algae are prokaryotes.  See eukaryotic cell.
prosimians  click this icon to hear the preceding term pronounced
the suborder of primates (Prosimii click this icon to hear the preceding term pronounced) that includes all of the lemurs, lorises, and related "primitive" primates.
prostate gland  click this icon to hear the preceding term pronounced
a gland surrounding the urethra at the base of the bladder.   It secretes most of the seminal fluid that is expelled with sperm cells during ejaculation.
protein  click this icon to hear the preceding term pronounced
any of a large number of organic molecules that are composed of one or more chains of amino acids.  These chains are twisted and folded back on themselves in complex patterns.  Proteins can serve a wide variety of functions through their ability to bind to other molecules.  Proteins may be transporting molecules in blood, structural components, enzymes, hormones, antibodies, or neurotransmitters.
proteome  click this icon to hear the preceding term pronounced
the full complement of proteins produced by an individual (or a species).  It is estimated that each human produces approximately 90,000 types of proteins.  See Human Genome Project.
protocultural  click this icon to hear the preceding term pronounced
referring to a very rudimentary culture.  Chimpanzees and possibly other great apes as well as our fossil ancestors 3-4 million years ago are said to have such a protoculture.  While they are dependent on their community's learned behavior patterns for survival, they do not have complex cultural technologies like humans.
proto-primates  click this icon to hear the preceding term pronounced
early primate-like mammals that evolved 65-60 million years ago, shortly after the end of the last dinosaurs.
Prototheria  click this icon to hear the preceding term pronounced
the subclass of mammal species in which females lay eggs like birds and reptiles.  However, they feed their newborn with mammary gland secretions like all other mammals.  The Prototheria are also referred to as monotremes, which literally means that they have only one opening for excretion and reproduction.  Included in this subclass are the platypus and echidna.
puberty  click this icon to hear the preceding term pronounced
the stage of maturation of an individual when secondary sexual characteristics begin to develop and sexual reproduction first becomes possible.  These changes are genetically controlled and triggered by hormones.
pulmonary edema  click this icon to hear the preceding term pronounced
a pneumonia-like accumulation of fluid and swelling in the lungs.  Like cerebral edema, it can be caused by hypoxia at high altitude.  While pulmonary edema is potentially life threatening, it generally is less likely than cerebral edema to result in death if treated in time.
punch flaking  click this icon to hear the preceding term pronounced
An Upper Paleolithic technique for making blade flakes.  After first preparing a rock core, a hard pointed punch (usually made from a deer antler tip) is placed near the edge of a striking platform and a percussion blow with a hammer to the top of the punch sends a controlled shock wave into the core which removes a thin, narrow blade flake.  Upper Paleolithic cores prepared for this technique were usually conical or cylindrical in shape with a relatively flat perpendicular striking platform at one end.
punctuated equilibrium  click this icon to hear the preceding term pronounced    (or punctuated evolution)
an evolutionary history in which a species remains essentially unchanged for hundreds of thousands or even millions of years and then experiences short periods of very rapid evolution.  The punctuated, or rapid change periods, are the result of major environmental changes in predation pressure, food supply, climate, etc.  During these times, natural selection may favor varieties that were previously at a comparative disadvantage.  The result is an accelerated rate of change in gene pool frequencies in the direction of the varieties that became the most favored by the new environmental conditions.  See phyletic gradualism. 
Punnett square  click this icon to hear the preceding term pronounced
a simple graphical method of showing all of the potential combinations of offspring genotypes that can occur and their probability given the parent genotypes.  Punnett squares are commonly used by genetics counselors to predict the odds of a couple passing on particular inherited traits.
purebred  click this icon to hear the preceding term pronounced
offspring that are the result of mating between genetically similar kinds of parents--the opposite of hybrid.  Purebred is the same as true breeding.
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quadrupedal  click this icon to hear the preceding term pronounced
having a four footed means of locomotion.  Humans are bipedal all other primates are primarily quadrupedal.

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race
any of the different varieties of humanity assumed by some people to exist, based on the discredited typological model of human variation.  Such "races" are commonly distinguished on the basis of visibly observable traits such as skin color, hair form, and body shape.  From a biological perspective, the term race should be reserved for distinct varieties or sub-species.  In the U.S. and other nations that use the concept of race, it refers mainly to culturally created realities rather than biological differences.
racemization
the process by which amino acids change from the L-molecule form to their mirror image D-molecule form.  This occurs naturally following the death of cells.  See amino acid racemization dating.
radiation
electromagnetic energy that is given off by an object.  Our bodies lose heat by radiation.  More specifically, we give off infrared radiation like the heat from a light bulb.
radiocarbon click this icon to hear the preceding term pronounced dating   (C-14 pronounce word)
a radiometric dating method based on the fact that the amount of carbon-14 steadily decreases in all organisms after death.  The reduction in the frequency of this isotope in a sample occurs at a half-life of 5730 ± 40 years.   This technique is used to provide chronometric dates for organic materials such as bone, shell, wood, and charcoal.
radiometric click this icon to hear the preceding term pronounced dating
referring to techniques for chronometric dating based on known half-lives of particular isotopes or the rate of other cumulative changes in atoms resulting from radioactivity.  Examples include electron spin resonance, fission track, potassium-argon, radiocarbon, and thermoluminescence dating.
random mating
mate selection in which all individuals have an equal chance of being selected--there is no conscious discrimination for or against any trait.  See non-random mating.
random sample
a sample that is selected by a researcher without any bias whatsoever.  In other words, all samples in a population have an equal probability of being selected.  This can be achieved by using a computer to randomly select the sample.

recessive allele  click this icon to hear the preceding term pronounced

an allele that is masked in the phenotype by the presence of a dominant allele.  Recessive alleles are expressed in the phenotype when the genotype is homozygous recessive (aa).

recombination

The creation of a new combination of genes on a chromosome that results from crossing-over.

red cell

see erythrocytes.

red-green color blindness    (or red-green color deficiency)

an X-linked genetically inherited color vision deficiency in which an individual cannot perceive red and green in the same way as people with normal vision.  This condition most often afflicts males.

regional continuity model          

a hypothesis to explain the origin of modern Homo sapiens.  It proposes that modern people evolved from archaic humans in Africa, Europe, and Asia.  In other words, modern African, European, and Asian people have considerable antiquity in their own continents.  See replacement model and assimilation model.

regulator gene

a gene that can initiate or block the functions of other genes.  Regulator genes control the timing of production of a variety of chemicals in humans and other organisms.  Shortly after conception, regulator genes work as master switches orchestrating the timely development of our body parts.  They are also responsible for changes that occur in our bodies as we grow older.  Regulator genes are also called homeotic genes click this icon to hear the preceding term pronounced.
relative date
a date that gives the time of an event only with reference to another event that is not worldwide in scale.  It only indicates that one event occurred earlier or later than another.  For instance, the observation that strata 2 is younger than strata 1 beneath it in a geological deposit does not provide information about how many years ago strata 2 was laid down.  It only indicates its age relative to strata 1.  In addition to the use of stratigraphy, relative dating methods include biostratigraphy and fluorine analysis dating.  See chronometric date.

replacement model

a hypothesis to explain the origin of modern Homo sapiens.  It proposes that modern people only evolved from archaic humans in Africa and that these new people expanded into Europe and Asia replacing all existing older populations.  In other words, we all have relatively recent African ancestry.  See regional continuity model and assimilation model.

replication (of DNA)

the process that occurs during the rest period (interphase) at the outset of mitosis and meiosis by which a DNA molecule is duplicated or copied.  One DNA molecule becomes two identical ones.  This is accomplished by the DNA molecule unwinding and unzipping along its base pairs so that both sides can be copied by free nucleotides.   Replication is triggered by an enzyme.
rhinarium  click this icon to hear the preceding term pronounced
a moist, hairless pad of skin at the end of a nose.  This is a characteristic of prosimians (except for tarsiers), dogs, and some other animals.
Rho-GAM  click this icon to hear the preceding term pronounced
a serum containing anti-Rh+ antibodies given to women at high risk for having a baby with erythroblastosis fetalis (i.e., Rh- women with Rh+ mates).  This must be done for the first and all subsequent pregnancies.  The injected antibodies quickly agglutinate any fetal red cells as they enter the mother's blood, thereby preventing her from forming her own antibodies.  Since the serum given the mother is a passive form of immunization, it will shortly leave her blood stream. 

ribosomal RNA  click this icon to hear the preceding term pronounced   (rRNA)

the RNA molecules that are located in the ribosomes.

ribosomes  click this icon to hear the preceding term pronounced

small structures usually near the surface of endoplasmic reticula in the cytoplasm of cells.  Ribosomes are the sites where proteins are assembled.  Each ribosome is composed of 3 RNA strands and 54 proteins woven into 2 separate, but entangled lumps.
Rickets disease  click this icon to hear the preceding term pronounced
a disease of the skeletal system in which the bones are softened and often bent as a result of vitamin D deficiency in the diet that hinders the normal development of bones and teeth.  Rickets most frequently affects malnourished children.
ritual  click this icon to hear the preceding term pronounced
a stylized and usually repetitive act that takes place at a set time and location.  Rituals are integral parts of religion, though not all rituals are religious in nature. 

RNA  click this icon to hear the preceding term pronounced   (ribonucleic acid click this icon to hear the preceding term pronounced)

a type of nucleic acid that is found in both the nucleus and the cytoplasm of cells.  Unlike DNA, RNA is single stranded.  Messenger RNA (mRNA) carries the genetic code from the DNA in the chromosomes and translates it with the help of transfer RNA (tRNA) at the site of the ribosomes in the cytoplasm in order to assemble, or synthesize, proteins.
robust
a term used by paleoanthropologists to refer to a big boned and muscular body.  The robust species of early hominins were Australopithecus robustus, boisei, and aethiopicus.
rotational north pole
the point on the northern extremity of the earth where the axis of rotation is located.  Compared to the magnetic north pole, the rotational one is relatively stable.

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sacculated  click this icon to hear the preceding term pronounced
referring to a stomach with "saccules," or sack-like compartments, in which bacteria slowly break down cellulose, thereby providing more useable calories.  Among the primates, only the Colobinae (colobus, langurs, and proboscis monkeys) have this characteristic.  Cows and some related animals also have sacculated stomachs.
sagittal crest  click this icon to hear the preceding term pronounced
a ridge of bone projecting up, from front to back, along the top midline of the skull.  It serves as a muscle attachment area for the temparalis muscles that extend up both sides of the head from the mandible (jaw).  The presence of a sagittal crest indicates that there are exceptionally strong jaw muscles.  Some Australopithecus afarensis and the robust australopithecines (Australopithecus robustus, boisei, and aethiopicus) had sagittal crests.  Among the living primates, the most prominent sagittal crests are found on adult male gorillas.  Humans do not have them.
savanna  click this icon to hear the preceding term pronounced
a tropical or subtropical grassy plains.  Savannas are usually the habitat of larger herbivores and their predators.  The first hominins apparently evolved on and near African savannas.
secondary oöcyte
see oöcyte.
sedimentary click this icon to hear the preceding term pronounced rock
rock formed from sediments usually eroded from older rock or inorganic remains of organisms (e.g., shells and skeletons).  Examples:  sandstone, shale, and limestone.
selectively permeable  click this icon to hear the preceding term pronounced
the characteristic of allowing only certain things to pass through.  Cell and nuclear membranes are selectively permeable.
selective pressure
environmental pressure that is placed on individuals within a population that results in change of the genetic makeup of the next generation.   Selective pressure is the driving force of natural selection.
semi-terrestrial  click this icon to hear the preceding term pronounced
referring to animals that spend much of their day on the ground but usually return to the trees to sleep.  See arboreal and terrestrial.
septum  click this icon to hear the preceding term pronounced
the soft tissue separating the two nostrils of a mammal's nose.
seriation  click this icon to hear the preceding term pronounced
a relative dating method based on the fact that artifact types change through time in frequency as a result of new technologies, styles, and available construction materials.  The frequency of artifact types in a stratum can be compared to known frequency changes previously recorded for an ancient culture.  In this way, the stratum can be dated relative to other strata or sites.  When a seriation sequence has been cross-calibrated with reliable chronometric dating methods, it can be considered a calibrated relative technique.
sex cell
a gamete, either a sperm or an ovum.  Sex cells are produced by the meiosis process and have a haploid number of chromosomes.  See somatic cell.
sex chromosome
the X and Y chromosomes which are responsible for determining whether an individual is a male or a female.  Normal males inherit an X from their mother and a Y from their father.  Normal females get an X chromosome from both parents.  See SRY gene.
sex-controlled gene
a gene that can be inherited by both genders but is usually expressed differently in males and females.  See sex-limited gene.
sex-limited gene
a gene that can be inherited by both genders but is usually expressed in only males or females.  See sex-controlled gene.
sex-linked
referring to a gene that is part of a sex chromosome.  Since all of the genes on a chromosome are inherited as a package, they are essentially linked together.
sexual dimorphism  click this icon to hear the preceding term pronounced
referring to anatomical differences between males and females of the same species.  Primate males are usually significantly larger and more muscular than females.  This is especially true of semi-terrestrial monkeys and the great apes.  Humans are also sexually dimorphic.
sexual skin or swelling
a nearly hairless large swollen patch of skin around the genital area of females that becomes very prominent when they are in estrus click this icon to hear the preceding term pronounced.  These areas swell with fluids and turn bright pink or red due to hormonal changes that occur in preparation for ovulation.  The sexual skin also produces odors that excite males of the species. They become highly attentive to the females at this time.  Sexual skins are found among many of the Old World monkey species in the subfamily Cercopithecinae (e.g., baboons) as well as the chimpanzees and bonobos.
shovel-shaped incisors
incisor teeth that have a "scooped out" appearance on the tongue side.  This pattern is characteristics of East Asian and Native American Populations today.  It was also common among Homo erectus.
sickle-cell trait  click this icon to hear the preceding term pronounced
a genetically inherited recessive condition in which red blood cells are distorted resulting in severe anemia and related symptoms that are often fatal in childhood.  Sickle-cell trait is the result of a pleiotropic gene.  People who are heterozygous for this trait rarely have these debilitating and ultimately fatal problems but do have a high degree of immunity to malaria.  Sickle cell trait is at its highest frequency among Central African populations and among people whose ancestors came from that region.  Sickle-cell trait is also known as sickle-cell anemia.
Sinanthropus pekinensis  click this icon to hear the preceding term pronounced
the original name given to the Homo erectus skeletal remains from the limestone cave site at Zhoukoudian click this icon to hear the preceding term pronounced near Beijing, China.  Sinanthropus pekinensis literally means "Chinese man from Peking" or Beijing.  It has also been called "Peking Man."
slash-and-burn
a traditional land-clearing practice whereby trees and other dense vegetation are cut with axes or machetes and later burned.  Ash from the burned vegetation provides fertilizer for agricultural crops that are planted among the remaining tree stumps.  Since no other fertilizer is usually applied, fields are abandoned after a few years, when crop yields go down, and clearing occurs elsewhere.  Traditional slash-and-burn farmers use simple, hand-held digging sticks instead of plows.
small population size effect
rapid changes in gene pool frequencies that can occur in small populations.  See genetic drift, founder principle, and bottleneck effect.
somatic cell  click this icon to hear the preceding term pronounced
all the cells in the body except those directly involved with reproduction.  Most cells in multicellular plants and animals are somatic cells.  They reproduce by mitosis and have a diploid number of chromosomes.  See sex cell.
spear thrower
a wood or bone rod with a hook on one end that fit into a socket at the base of a spear.  This device was used by the Cro-Magnon and other people with Upper Paleolithic technologies to push off spears.  It increased the range and force of impact of projectiles by essentially increasing the length of the spear thrower's arm.  The spear thrower is also known as an atlatl click this icon to hear the preceding term pronounced.
special creation
the idea that all life forms were created by God as separate, distinct species.  The implication is that they do not change through time and that there is no evolutionary relationship between different species.  
speciation  click this icon to hear the preceding term pronounced
the evolution of new species from older ones.  When this occurs in a single evolutionary line without branching, it is referred to as successive speciation click this icon to hear the preceding term pronounced and results in the pattern of evolution known as anagenesis click this icon to hear the preceding term pronounced.
species  pronounce word
the largest natural population of organisms that can potentially interbreed to produce fertile offspring.  It is commonly assumed that members of one species are reproductively isolated from members of all other species (i.e., they cannot mate with them to produce fertile offspring).  However, we must be cautious in defining species with this criterion because members of very closely related species can sometimes produce offspring together, and a small fraction of those may be fertile to some degree.  This is the case with mules, which are the product of mating between horses and donkeys.  About one out of 10,000 mules is fertile.  This suggests that some species differences are a matter of degree.  See morphospeices, biospecies, and paleospecies.
sperm  click this icon to hear the preceding term pronounced
a male sex cell or gamete.
spermatogenesis  click this icon to hear the preceding term pronounced
the meiosis process of male sex cells that produces sperm.  It takes place in the testes of humans and other male animals.
spina bifida  click this icon to hear the preceding term pronounced
a neural tube birth defect in which there are malformations of vertebrae and the protrusion of the spinal cord from the body.  This can result in paralysis of the legs, loss of bowel and bladder control, and "water" on the brain (hydrocephaly).   Spina bifida requires surgical correction.
SRY gene  click this icon to hear the preceding term pronounced
sex-determining region Y gene.   A gene on the Y chromosome which, if present and functioning, causes the undifferentiated sex organs of an animal embryo to become testes.  These then produce the hormone testosterone which, in turn, causes the development of masculine physical traits.
stabilizing selection
Selection against extreme forms of a trait.  In the case of polygenic traits that are expressed as a continuum of phenotypes, such as human stature, it would be selection for people who are in the middle of the range and against those who are very tall or very short.  The result would be fewer people who are at the extremes in height.  In the case of a trait controlled by only two alleles, it would be selection against both homozygotes and for the heterozygote.  An example is nature selecting for people who are heterozygous for the sickle cell allele in a malarial environment.  See directional selection and disruptive selection.
standard deviation
a statistical measure of the dispersion (or spread) from the arithmetic mean (or average) of a group of scores.  Chronometric dates derived with a radiometric method are published with a "plus or minus" factor, which usually is a range of dates within one standard deviation above and below the mean.  This should be read as a 67% likelihood that the actual date falls within the given range.
stem cells  click this icon to hear the preceding term pronounced
embryonic cells that have not yet become specialized tissue cells--they potentially can develop into any type of tissue in the body.  Children and adults retain somewhat specialized stem cells in their bone marrow.  These stem cells are the source of the major blood cells--erythrocytes, leukocytes, and thrombocytes (platelets).
stereoscopic vision  click this icon to hear the preceding term pronounced
the ability to see things in three dimensions (3-D).   Stereoscopic vision is what allows for true depth perception.  See peripheral vision and binocular vision.
stratigraphy  click this icon to hear the preceding term pronounced
the study of geological strata, or layers of rock or soil, usually for relative dating based on the principle of superposition.
stuttering alleles
defective alleles that have segments which are doubled in their transmission from generation to generation.  In the case of genetically inherited diseases, the result is increasingly severe symptoms each generation.  The myotonic form of muscular dystrophy is an example.  Stuttering alleles are also known as unstable alleles.
subadult  click this icon to hear the preceding term pronounced
the stage of maturation in which animals are beyond infancy and early childhood but are not yet fully grown.
subphyla  click this icon to hear the preceding term pronounced
the plural of subphylum (the level of classification immediately below phylum and above class in the Linnaean classification system).
subsistence pattern
referring to sources of food and the way they are obtained (e.g., scavenging, hunting, and farming).  Subsistence base is another name for subsistence pattern.  "Subsistence strategy" refers to decisions made by people as to the best way to obtain food in a particular environment (e.g., diversified foraging, specialized big game hunting, etc.).
subarctic
referring to climatic regions that are next to the arctic circle (e.g., Northern Alaska and Northern Canada) and that have extremely long cold winters with a great deal of snow and little or no day light.  Subarctic regions are farther north than temperate ones in the northern hemisphere.
subtropical
referring to climatic regions in between tropical and temperate zones.  Subtropical areas rarely have winter snow and are warm enough to grow oranges and avocados.
successive speciation  click this icon to hear the preceding term pronounced
see speciation.
supraorbital tori  pronounce word   (singular: supraorbital torus)
prominent projecting bony bars or brow ridges above the eyes.  This trait was characteristic of Homo erectus and some other early humans.
survival of the fittest
the idea that those individuals in a species that have characteristics selected for by nature are biologically the most fit.  They are the ones who more frequently survive to be the parents of the next generation.  The fittest individuals are not necessarily the strongest, largest, quickest, or smartest.  This concept was central to Charles Darwin's idea of natural selection.
suspensory climbing
see brachiators.
suture  click this icon to hear the preceding term pronounced   (in relationship to skulls)
the irregular line of joining between two bones, especially between the bone plates of the skull in vertebrates.
symbol  click this icon to hear the preceding term pronounced
a thing, such as a word, that can represent something else that is not here and now.  The meaning of a symbol is arbitrary and is given by those who use it.  Human languages are systems of symbols.
syndromes  click this icon to hear the preceding term pronounced
a number of conditions that occur together and characterize a particular disease or condition (e.g., Klinefelter syndrome).
sympathetic magic
a magical practice based on the principle that like causes like.  For those who believe that this works, it would be possible to cause another person or animal harm by making an image of them and doing something to harm the image such as painting a spear sticking into the body.  The animal of whom the image is a likeness would supposedly suffer the same effects.  The Cro-Magnon cave paintings of animals being wounded or pregnant was very likely attempts to use sympathetic magic to cause the same effects on the real animals.  Sympathetic magic is also called imitative magic.
synthetic  theory of evolution  click this icon to hear the preceding term pronounced
the 20th century conception of evolution being caused by a number of complex and often interacting processes.  This is essentially a combination of Darwin's concept of natural selection, Mendel's basic genetics, along with the facts and theories of population genetics and molecular biology.

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tactile pad  click this icon to hear the preceding term pronounced
a skin surface that is unusually sensitive to pressure, temperature, and pain because there are high concentrations of nerve endings immediately below these areas.
taphonomy  click this icon to hear the preceding term pronounced
the study of the conditions under which plants, animals, and other organisms become altered after death, buried, and sometimes preserved as fossils.
taxonomy  click this icon to hear the preceding term pronounced
naming, describing, and classifying organisms into different categories on the basis of their appearance and other diagnostic characteristics as well as their evolutionary relationships.  The biological sciences primarily use the Linnaean classification system for this purpose.
Tay-Sachs Disease  click this icon to hear the preceding term pronounced
a genetically inherited condition caused by the inability to produce the enzyme hexosaminidase A.  This results in progressively increased fluid pressure on the brain and the subsequent degeneration of the brain and nervous system beginning about 6 months of age and inevitably resulting in death usually by age 2-3.  The gene responsible for Tay-Sachs Disease is recessive.  It has been most common among the descendents of Eastern European Jews (Ashkenazi Jews).
tectonic click this icon to hear the preceding term pronounced movement
lateral and/or vertical movement of segments of the earth's crust.  The continents and the ocean floors consist of tectonic plates that are moving relative to each other.  On average, such movements are about 1 inch per year.
tectonics  click this icon to hear the preceding term pronounced
the study of the earth's crustal structures, such as continental plates, and the forces that cause them to change shape and move relative to each other.  See tectonic movement.
temperate
referring to climatic regions between subtropical and subarctic zones.  Temperate areas usually have winter snow and are too cold to grow oranges and avocados.  However, summer temperatures can be warm.
temporal
referring to the temple regions high on the sides towards the front of the head.
teratogen  click this icon to hear the preceding term pronounced
a mutagen that can cause a mutation in a sex cell. Such mutations can be inherited.  Mutations that occur only in somatic cells are not inherited, though they can result in cancer.
terrestrial  click this icon to hear the preceding term pronounced
referring to animals that spend most of their time on the ground rather than in the air, water, or trees.  See arboreal and semi-terrestrial.
territorial defense behavior
active defense by community members of their shared home range or territory.  Many species of non-human primates use scent marking, loud vocalizations, or threat gestures to defend their territories against incursions by other communities of their species.
testosterone  click this icon to hear the preceding term pronounced
a class of masculinizing hormones.   Both men and women produce them, but males normally produce much more.   Testosterone is mainly produced in the testes of males.   Smaller amounts are produced by the cortex of the adrenal glands in both males and females.
thalassemia  click this icon to hear the preceding term pronounced
a group of genetically inherited forms of anemia caused by the production of fragile hemoglobin molecules that are easily destroyed.  Thalassemia is most common around the Mediterranean Basin and in Southeast Asia.  As in the case of sickle-cell trait, and glucose-6-phosphate dehydrogenase deficiency, it may provide some immunity to malaria.
Theria  click this icon to hear the preceding term pronounced
the subclass of mammal species that include the marsupials and placental mammals.
thermoluminescence click this icon to hear the preceding term pronounced dating   (TL)
a radiometric dating  method based on the fact that trace amounts of radioactive atoms, such as uranium and thorium, in some kinds of rock, soil, and clay produce constant low amounts of background ionizing radiation.  The atoms of crystalline solids, such as pottery and rock, can be altered by this radiation.  Specifically, the electrons of quartz, feldspar, diamond, or calcite crystals can become displaced from their normal positions in atoms and trapped in imperfections in the crystal lattice of the rock or clay molecules.  These energy charged electrons progressively accumulate over time.  When a sample is heated to high temperatures in a laboratory, the trapped electrons are released and return to their normal positions in their atoms.  This causes them to give off their stored energy in the form of light impulses (photons).  This light is referred to as thermoluminescence (literally "heat light").  A similar effect can be brought about by stimulating the sample with infrared light.  The intensity of thermoluminescence is directly related to the amount of accumulated changes produced by background radiation, which, in turn, varies with the age of the sample and the amount of trace radioactive elements it contains.
thermoremanent magnetism  click this icon to hear the preceding term pronounced
magnetic fields that are altered or formed in atoms of iron by heat in excess of 1100° F. (600° C.).  Such fields line up with the magnetic field of the planet at the time of the exposure to a high temperature.  They will remain oriented to that direction indefinitely despite the fact that the true position of magnetic north wanders over thousands of miles around the rotational north pole and even reverses with the magnetic south pole over longer periods of time.   See paleomagnetic dating.
thrombocytes  click this icon to hear the preceding term pronounced
a type of blood cell that coagulates and clots blood when there is an injury to a blood vessel.  Thrombocytes are also called platelets.  See stem cells.
thyroid  click this icon to hear the preceding term pronounced
the large gland in the neck next to the trachea that secretes the hormone thyroxine, which regulates body growth and metabolism.
toggle-head harpoon  click this icon to hear the preceding term pronounced
a bone or antler harpoon tip or point with a hole for attaching a rope.  It is designed so that when the harpoon is thrust into the body of a large animal, the wooden shaft falls off.  The hunter keep holds of the animal with the rope attached to the toggle-head harpoon point stuck in its body.
transfer RNA   (tRNA)
a form of RNA that binds to specific amino acid molecules and transports them to the ribosomes for the assembly of proteins.   Transfer RNA molecules temporarily bond with corresponding messenger RNA codons at the ribosomes in this process of protein synthesis. 
translocation
a structural modification of a chromosome in which a portion of a chromatid is broken off and attached to a different location on that chromosome or on another chromosome.  This occurs as a result of crossing-over.
tree-ring dating
see dendrochronology.
triple-X female
see metafemale.
trisomy  click this icon to hear the preceding term pronounced
the form of aneuploidy in which there are 3 chromosomes instead of just 2 for a specific homologous pair.  An example is the common form of Down syndrome in which there are 3 chromosome 21's.  Most fetuses with autosomal trisomies die before birth.
trisomy 18  click this icon to hear the preceding term pronounced
a rare chromosomal abnormality  in which there is a trisomy of chromosome 18.  This inherited condition is also called Edward's syndrome.  It is characterized by severe mental retardation, a small head with malformed ears set low, and a face with a pinched appearance.  Other likely defects include a cleft palate, webbed hands, missing thumbs, clubfeet,  as well as heart and genitourinary defects.  Individuals with trisomy 18 usually die within a few months after birth.
trisomy 21  click this icon to hear the preceding term pronounced
see Down syndrome.
tropical
referring to the usually warmest climatic regions.  They are mostly found within 20°-30° latitude from the Equator.  All human evolution until relatively late Homo erectus occurred in the tropics, especially in Africa.  See subtropical and temperate.
true breeding
see purebred.
tundra   click this icon to hear the preceding term pronounced
cold, treeless regions having permanently frozen subsoil (permafrost click this icon to hear the preceding term pronounced) that only supports extremely hardy low-growing vegetation such as lichens, mosses, and stunted shrubs (in the summer).

Turner syndrome  click this icon to hear the preceding term pronounced

a genetically inherited sex chromosome abnormality only affecting females.  Women with Turner's only have one X chromosome--their genotype is X0.   These individuals are short in stature, averaging 4'7" and have distinctive webbed necks (i.e., extra folds of skin).  They have exceptionally small breasts and generally lack secondary sexual characteristics.  Their ovaries do not develop normally and they do not ovulate.  They are in a sense postmenopausal from early childhood and are sterile.  In some individuals, there is slight mental retardation.   Turner syndrome is rare--current estimates of its frequency range from 1 in 3000 to 1 in 10,000 females.

typological  model  click this icon to hear the preceding term pronounced   (of human variation)

a system for classifying people based on the false assumption that humans can be unambiguously placed into "races" on the basis of selected traits such as skin color, hair form, and body shape.  Advocates of this approach incorrectly believe that there are more or less distinct populations of people from different geographic regions.  Negroid, Mongoloid, and Caucasoid are examples of typological groupings.
typological viewpoint   (of classifying species from fossils)
the idea that if two fossils look slightly different, they must be categorized as being from two different species.  This approach emphasizes minor differences.  People who maintain this approach are generally referred to in the biological sciences as "splitters".  See populationist viewpoint.

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- U -

ultrasound monitoring
the use of high frequency sound to form an image or picture of internal organs for immediate medical diagnostic purposes.  The Ultrasonography device transmits sound waves directly into the body and then accurately records the amount of time for echoes to return to a receiver, much like radar.  The sound waves used are at frequencies above the threshold of human hearing--e.g., 20,000 vibrations per second.
ultraviolet radiation  click this icon to hear the preceding term pronounced
electromagnetic radiation ranging in wave length just beyond violet in the visible spectrum of light.  The human eye cannot detect u.v.  Our sun is the major source of u.v. radiation on earth.  Prolonged exposure to u.v. can result in destructive skin burns and can promote the onset of skin cancer.
undernourishment  click this icon to hear the preceding term pronounced
severe deficiency of calories in the diet. Prolonged undernourishment can result in marasmus which is a wasting away of the body.  See malnourishment.
uniface
a stone tool that is shaped only on one face or side.  See biface.
uniformitarianism  click this icon to hear the preceding term pronounced
the late 18th century theory of James Hutton that the natural forces now changing the shape of the Earth's surface have been operating in the past much in the same way.  The most important implication is that the Earth is very old and that the present is the key to understanding the past.  Elaborated on by Charles Lyell in the 19th century, this theory opposed catastrophism.
unit inheritance
Gregor Mendel's idea that the characteristics of parents are passed on to descendants unchanged as units.  In other words, the hereditary material of any organism is made up of discrete units (now called genes).
universal donor
someone who has type O blood.  Such people lack antigens for the ABO blood system.  As a result, their blood will not be agglutinated when it is transfused into people with any other ABO type.
universal receiver
someone who has type AB blood. Such people do not produce antibodies for the ABO blood system.  As a result, they can receive transfusions from people with any ABO type without agglutinating it.
universal time scale
a time scale, or calendar, that can be used any place in the world since it has a finite beginning point from which any earlier or later event can be related exactly.  All chronometric dates are given in terms of a universal time scale.
unstable alleles
see stuttering alleles.
Upper Paleolithic
the last part of the Paleolithic click this icon to hear the preceding term pronounced stage of development in which Cro-Magnon and other late ice age modern Homo sapiens developed a number of sophisticated stone tool making traditions including the Magdalenian.  This was the height of technical sophistication during the Old Stone Age.  The Upper Paleolithic in Europe began about 40,000 years ago and ended around 10,000 years ago.  Technological developments leading to the Upper Paleolithic may have begun somewhat earlier in Africa.
uranium series dating
a group of dating techniques based on measurement of the radioactivity of short-lived daughter isotopes of uranium.
uranium-thorium click this icon to hear the preceding term pronounced dating
a radiometric dating technique based on the rate at which uranium-238 and thorium-230 fission.  This method has been used to date organic marine sediments, bone, wood, coral, stone, and soil from deep water, cave, or land fall areas.  The time range that has been dated with this method so far is less than 300,000 to about 1,000,000 years ago.  The half-life of U-238 is 4.468 billion years and the half-life of Th-230 is 75,380 years.  This is one of several uranium series dating methods. 
use-disuse theory
see inheritance of acquired characteristics.

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- V -

variable penetrance
the expression of a genetically inherited trait in different forms or degrees in different people.  For example, the alleles for the Down syndrome genes may cause an effect in the phenotype of some individuals but not others.  As a result, there is considerable variability within the Down syndrome population in regards to susceptibility to the characteristic unpleasant medical problems. 
varve click this icon to hear the preceding term pronounced analysis
a calibrated relative or potentially chronometric dating technique based on counting annual silt deposits (i.e., varves) in former lakes resulting from the summer melt of glaciers.  In Scandinavia, this geological clock has been used to date associated archaeological evidence from the melt years of the last ice age, which began its final retreat about 15,000 years ago.
vasoconstriction  click this icon to hear the preceding term pronounced
constriction or narrowing of blood vessels so that a decrease in flow occurs.  See vasodilation.
vasodilation  click this icon to hear the preceding term pronounced
enlargement in the diameter of blood vessels so that an increased flow occurs.  See vasoconstriction.
ventral  click this icon to hear the preceding term pronounced
see dorsal.
Venus figurines  click this icon to hear the preceding term pronounced
small carvings of women that could fit into the hand made by the Cro-Magnon people.  They were not portraits but rather faceless idealized representations of well fed, healthy, usually pregnant women with large buttocks.  Because of these characteristics, they are thought by most paleoanthropologists to be ritual objects symbolizing female fertility.  Many of these stylized carvings are reminiscent of modern abstract art.  Venus figurines were made from 27,000 years ago down to the end of the last ice age 10,000 years ago. 
Vertebrata  click this icon to hear the preceding term pronounced
the subphylum of chordates that includes the animals that possess a spinal chord protected by a segmented vertebral column of cartilage and/or bone.
vertebrates  click this icon to hear the preceding term pronounced
members of the animal subphylum Vertebrata.
vestigial  click this icon to hear the preceding term pronounced
referring to body parts that are remnants of parts that were more fully developed and functional in an earlier stage of evolution in the species.

virus  click this icon to hear the preceding term pronounced

a category of extremely small microscopic parasites of plants, animals, and bacteria. Viruses are not cells but rather RNA or DNA molecules surrounded by a protein coating.  Since viruses cannot reproduce without a host cell, they are not strictly speaking living organisms.  There are many kinds of viruses.
vocalizations  click this icon to hear the preceding term pronounced
sounds produced primarily by the throat and mouth.  Primate vocalizations include a wide variety of hoots, whistles, grunts, etc.

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- W -

Wernicke's area  click this icon to hear the preceding term pronounced
a small area of the human brain that is involved in the comprehension of speech.  It is located in the cerebral cortex click this icon to hear the preceding term pronounced.  See Broca's area for illustration.
white cells
see leukocytes.

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- X -

X-linked  click this icon to hear the preceding term pronounced
referring to a gene that is carried by an X chromosome.  See sex-linked gene.
XXX syndrome  click this icon to hear the preceding term pronounced
see metafemale.
XYY syndrome  click this icon to hear the preceding term pronounced
a genetically inherited sex chromosome abnormality only affecting males.  Men with XYY syndrome inherit an extra Y chromosome--their genotype is XYY.  They are usually quite tall (i.e., above 6 feet) and generally appear and act normal.  During adolescence, they frequently have severe facial acne.  They are usually fertile and lead ordinary lives as adults.  Many, if not most, are unaware that they have a chromosomal abnormality.  The frequency of XYY syndrome is not certain due to statistical differences between different studies of this condition.  It may be as common as 1 in 900 male births to as rare as 1 in 1,500 or even 1 in 2,000. 

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- Y -

Y-linked  click this icon to hear the preceding term pronounced
referring to a gene that is carried by a Y chromosome.  See sex-linked gene.

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- Z -

zygomatic arch  click this icon to hear the preceding term pronounced
a bony arch extending horizontally on either side of the face just below the eyes on primates and many other vertebrates.   The major jaw muscles pass under these two arches on their way up to the temporal areas of the skull for attachment.
zygote  click this icon to hear the preceding term pronounced
a "fertilized" ovum.  More precisely, this is a cell that is formed when a sperm and an ovum combine their chromosomes at conception.  A zygote contains the full complement of chromosomes (in humans 46) and has the potential of developing into an entire organism.

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Copyright © 2005-2014 by Dennis O'Neil. All rights reserved.