The process by which populations of organisms respond to long term environmental stresses by permanent genetic change—i.e., evolution.

The process by which individual organisms respond to environmental stresses during their lifetime without changing genetically. These changes are generally not inheritable.

Temporary changes in the body in response to environmental stresses such as high or low temperatures, intense ultraviolet radiation from sun light, or high altitude. These anatomical and physiological changes are usually reversible. Example: developing a suntan in the summer and losing it in the winter.

acclimatization or acclimatory adjustment

A change in the normal growth patterns and development of an individual that occurs in childhood as a result of specific cultural practices 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 or developmental acclimatization

An inadequacy or an excess of some key element(s) in the diet, such as proteins or specific minerals and vitamins.

A severe deficiency of calories in the diet.

The medical condition resulting from prolonged undernourishment. Symptoms include extreme emaciation, diarrhea, anemia, and apathy. Children who survive this condition usually develop short adult stature and some degree of permanent brain damage.

The medical condition of babies and very young children resulting from a severe protein deficiency in their diet. 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 this disease are likely to have their growth retarded. It usually results from a child being weaned too early and being forced to subsist mainly on a high carbohydrate and low protein diet.