Evolutionary adaptation

What is evolutionary adaptation?

An adaptation may be defined as an inherited and reliably developing characteristic that came into existence through natural selection because it helped to solve a problem of survival or reproduction during the period of its evolution.

Let’s break down this definition into its core elements. An adaptation must have Genes “for” that adaptation. … The fact that genes are required for adaptations, however, does not mean that human behavior is “genetically determined”. Past environments selected the genes we have today; environments during a person’s lifetime are necessary for the proper development of adaptations, and current environments are responsible for activating adaptations once they have developed.

An adaptation must develop reliably among species members in all “normal” environments. … There are important exceptions to this, such as mechanisms that exists in only one sex or in a specific subset of the population. … The reliably developing feature of adaptations does not mean that the adaptation must appear at birth. Indeed, many adaptations develop long after birth.

Adaptations are fashioned by the process of selection. …

Those characteristics that make it through the filtering process in each generation do so because they contribute to the solution of an adaptive problem of either survival or reproduction better than alternative (competing) designs existing in the population. …

Each adaptation has its own period of evolution. (See Environment of evolutionary adaptation). —p39-40, Evolutionary psychology (book)

George Williams:

The third contribution of Adaptation and natural selection was Williams’s careful analysis of adaptation, which he referred to as “an onerous concept”. Adaptations may be defined as evolved solutions to specific problems that contribute either directly or indirectly to successful reproduction. Sweat glands, for example, may be adaptations that help solve the survival problem of thermal regulation. … The problem is how to determine which attributes of organisms are adaptations. Williams established several standards for invoking adaptation and believed that it should be invoked only when necessary to explain the phenomenon at hand. When flying fish leaps out of a wave and falls back into the water, for example, we do not need to invoke an adaptation for “getting back to water.” This behavior is explained more simply by the physical law of gravity, which explains why what goes up must come down.

In addition to providing conditions in which we should not invoke the concept of adaptation, Williams provided criteria for determining when we should invoke the concept: reliability, efficiency, and economy:

Reliability: Does the mechanism regularly develop in all members of the species across all “normal” environments and perform dependably in the contexts in which it is designed to function?

Efficiency: Does the mechanism solve a particular adaptive problem well?

Economy: Does the mechanism solve the adaptive problem without extorting huge costs from the organism?

In other words, adaptation is invoked not merely to explain the usefulness of a biological mechanism, but to explain improbable usefulness. Hypotheses about adaptations are, in essence, probability statements about why a reliable, efficient, and economic set of design features could not have arisen by change alone. —p16-17, Evolutionary psychology

Geoffrey Miller:

If a trait in the human mind has evolved to have a specific function through natural selection, first, this trait should vary little between individuals. This is because non-adaptive variation would have been eliminated by selection long ago. Second, heritability must be low. This is because genes other than the optimal genes would also have been eliminated by selection. Third, it must be efficient and low cost. This is because natural selection favors efficient problem solving. Fourth, it should be modularized and specialized for solving particular problems (see Domain-specific module). Because this is an effective way to deal with the problem. —p204