The Evolutionary Psychology FAQ

Edward H. Hagen, Institute for Theoretical Biology, Berlin

What is an adaptation?

Adaptations solve reproductive problems, that is, adaptations have functions. The lungs are an adaptation, and their function is to transfer gases to and from blood. Muscles are an adaptation, and their function is to apply force to various parts of the body. The function of intestines is (in part) to extract nutrients from food. In general, all members of a species of the same sex and developmental stage share the same functional organization (i.e., have the same adaptations). All humans have bones, muscles, hearts, eyes, etc. While some problem solving abilities (functions) of the nervous system are obvious (e.g., vision), many are not; the goal of evolutionary psychology is to identify all functions of the nervous system.

Functional organization implies specialization. Oxygenating blood is a different problem than circulating blood, and it would be difficult if not impossible for a single functional unit to effectively solve both problems. Efficiently transferring oxygen to blood requires very high surface areas of gas permeable tissue that would be quite unsuitable for pumping fluids. The nervous system is clearly specialized as well. Generating the relatively low bit rate serial streams that characterize speech is a very different problem from parallel processing the vast amount of data generated by the retinas. The nervous system appears to be composed of multiple, specialized, functional units. This begs the question, how many specialized functional units are there? A few moments of reflection reveals that there are least several: vision, hearing, speech, motor control, sensation, smell, memory. Are there only a few more than these, or many more?

Finally, functional organization appears in the world only as a product of natural selection. Thus, the domains about which functions are organized are the domains that are relevant to fitness. Organisms possess precisely those functions that facilitated survival and reproduction in past environments. Any distinction in the world that could be exploited by an organism to increase its fitness represents a selection pressure. The set of such selection pressures that has acted on the human lineage is often referred to as the Environment of Evolutionary Adaptedness (EEA). Such selection pressures may or may not have resulted in the evolution of adaptations that exploit these distinctions to the benefit of the organism (and thus the genes that code for such adaptations). A complete specification of all selection pressures that have acted on a population over evolutionary time places an upper bound on the number of adaptations that can evolve. In the absence of constraints, one adaptation would evolve for each distinct selection pressure. The view outlined here implies that any organism can be partitioned into a finite number of functional components, and that such a partition in some sense constitutes a complete specification of the organism. This model of life is quite tractable, and has resulted in tremendous advances in biology.

Copyright 1999-2002 Edward H. Hagen