Adaptations as Key to Evolution. Human Adaptation—Genetic and Cultural

Adaptation is the key to understanding evolution. The word species has several meanings. The taxonomic species is that determined by the museum systematist; it is essential for physiologists to know the proper names of animals and plants on which they experiment. The cladistic species is determined by some arbitrary number of differences, usually computer-based. The biological species applies to kinds of animals (or plants) that are reproductively isolated, populations within which no gene exchange can occur.

The geographic species applies to organisms that reproduce parthenogenetically or by occurrence of hybrids. The physiological species is based on unique adaptations to ecological niche and geographic range. This is the species of critical adaptation and subsequent selection. In some animals, variations in adaptations leading to speciation is rapid (e.g., in field mice); in other animals, adaptive variation is very slow (e.g., in horseshoe crabs).

Human Adaptation—Genetic and Cultural. The preceding sections summarize the principles of biological adaptation. Undoubtedly, human evolution has occurred by selection of many inherited characters, and humans in different environments can vary within genetically determined limits in critical characters much as can populations of other animals. Examples of structure adaptations include skeletal elements that allow for bipedalism with resulting freedom of use of forelimbs. Human metabolic adaptations allow for an omnivorous diet, enzymes for processing all classes of foods (except cellulose and related polysaccharides). In respiration and circulation, there are adaptations for airbreathing even at reduced 0₂ levels and for vasomotor responses to physical stresses.

The adaptations of the endocrines permit life under highly complex conditions. An important biological adaptation of humans is the long prepubertal period that allows extensive physiological development before reproduction is possible. The most distinctive biological feature of humans is the speech area of the cerebral cortex. Development of Broca’s and Wernicke’s areas permit a variety of meaningful vocal communications not possible in subhumans. Genetic differences determine individuality (blood types, eye color, temperament); genetic differences are also ethnic (skin color, body size).

However, despite genetic differences, all humans constitute a single species in that they can interbreed. Humans evolved in central Africa where a coat of hair would likely be a liability. However, use of protective animal skins as protective covering has allowed extension of range without extensive physiological acclimation of temperature tolerance.

In parallel with the variety of genetically based adaptations, humans have undergone social evolution and adaptations based on cultural characters are fully as important as the biological adaptations. Many kinds of animals live in social groups and behavior of these social groups has often been interpreted in anthropomorphic terms. Individuals in a colony of Hymenoptera perform different functions, and colonies of bees and termites have been called superorganisms.

The social behavior of many birds and animals that live in colonies has a genetic basis with limited adaptive change during development and learning. Cultural evolution in humans is transmitted not genetically but by behavioral trans mission from generation to generation. By selection of cultural traits a very different set of adaptations has evolved.

A few examples of culturally transmitted adaptations are (1) societies for common functions—altruism to nonkin, rules of conduct (moral behavior); (2) language that goes beyond symbolic use of sound to abstract uses of words; (3) technology, including communal preparation of food, agriculture, and development of machines; (4) representation of nature and human moods in art, music, and dance; (5) belief in superhuman forces to explain events not explicable by human experience; and (6) population dispersal, migration, and exploration of the world, unlike migration for reproduction.

Cultural inheritance adds a new dimension to biological inheritance. In general, the range of genetically determined function and normal function under stresses is wide for molecules-proteins and lipids. The range is narrower when molecules are organized in cells and tissues and still narrower for integrated whole organisms. The characters of cultural inheritance widen the range of tolerance; i.e., cultural inheritance reverses the trend of biological inheritance.

In its broadest context, adaptation to physical and biotic environment gives a basis for understanding biological evolution and also the development of human civilization.