In this
tutorial you will be learning about the Linnaean
system of classification used in the biological sciences to describe and categorize all
living things. The focus is on finding out how humans fit within this system.
In addition, you will discover part of the great diversity of life forms and come to
understand why some animals are considered to be close to us in their evolutionary
history.
How
many species are there?
This is not an easy question to answer. About 1.8 million have been given scientific names. Thousands more are added to the list every year. Over the last half century, scientific estimates of the total number of living species have ranged from 3 to 100 million. The most recent methodical survey indicates that it is likely to be close to 9 million, with 6.5 million of them living on the land and 2.2 million in the oceans. Tropical forests and deep ocean areas very likely hold the highest number of still unknown species. However, we may never know how many there are because it is probable that most will become extinct before being discovered and described.
The tremendous diversity in life today is not new to our planet. The noted paleontologist Stephen Jay Gould estimated that 99% of all plant and animal species that have existed have already become extinct with most leaving no fossils. It is also humbling to realize that humans and other large animals are freakishly rare life forms, given that 99% of all known animal species are smaller than bumble bees.
Why
should we be interested in
learning about the diversity of life?
In order to fully understand our own biological evolution, we need to be aware that humans are animals and that we have close relatives in the animal kingdom. Grasping the comparative evolutionary distances between different species is important to this understanding. In addition, it is interesting to learn about other kinds of creatures.
When
did scientists begin classifying living things?
Before the advent of
modern, genetically based evolutionary studies, European
and American biology consisted primarily of taxonomy
, or classification of organisms into different categories based
on their physical characteristics and presumed natural
relationship. The leading naturalists of the 18th and 19th centuries
spent their lives identifying and naming newly discovered plants and animals.
However, few of them asked what accounted for the patterns of similarities and differences
between the organisms. This basically nonspeculative approach
is not surprising since most naturalists two centuries ago held the view that plants and
animals (including humans) had been created in their present form and that they have
remained unchanged. As a result, it made no sense to ask how organisms have evolved through time. Similarly, it was
inconceivable that two animals or plants may have had a common ancestor or that extinct
species may have been ancestors of modern ones.
 |
|
| Carolus Linnaeus 1707-1778 |
One of the most important
18th century naturalists was a Swedish botanist and medical doctor named Karl von Linné. He wrote 180 books mainly describing plant species in extreme detail.
Since his published writings were mostly in Latin, he is known to the scientific world
today as Carolus Linnaeus
, which is the Latinized form he
chose for his name.
In 1735, Linnaeus published an influential book entitled Systema Naturae in which he outlined his scheme for classifying all known and yet to be discovered organisms according to the greater or lesser extent of their similarities. This Linnaean system of classification was widely accepted by the early 19th century and is still the basic framework for all taxonomy in the biological sciences today.
The Linnaean system uses
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. Such a dual level
designation is referred to as a binomial nomenclature
or binomen
(literally
"two names" in Latin). For example, Linnaeus described
modern humans in his
system with the binomen Homo sapiens
,
or "man who is wise". Homo is our
genus and sapiens is our species.
| genus | genus | ||
|---|---|---|---|
| species | species | species | species |
Linnaeus also created
higher, more inclusive classification categories. For instance, he placed all
monkeys and apes along with humans into the order Primates
. His use of the word Primates (from the
Latin primus meaning "first") reflects the human centered world view of
Western science during the 18th century.
It implied that humans were "created" first. However, it also
indicated that people are animals.
| order | |||||||
|---|---|---|---|---|---|---|---|
| family | family | ||||||
| genus | genus | genus | genus | ||||
| species | species | species | species | species | species | species | species |
