Editing Evolutionary psychology (section)

===Products of evolution: adaptations, exaptations, byproducts, and random variation===
Not all traits of organisms are evolutionary adaptations. As noted in the table below, traits may also be [[exaptation]]s, byproducts of adaptations (sometimes called "spandrels"), or random variation between individuals.<ref>Buss et al. 1998</ref>

Psychological adaptations are hypothesized to be innate or relatively easy to learn and to manifest in cultures worldwide. For example, the ability of toddlers to learn a language with virtually no training is likely to be a psychological adaptation. On the other hand, ancestral humans did not read or write, thus today, learning to read and write requires extensive training, and presumably involves the repurposing of cognitive capacities that evolved in response to selection pressures unrelated to written language.<ref>Pinker, Steven. (1994) The Language Instinct</ref> However, variations in manifest behavior can result from universal mechanisms interacting with different local environments. For example, Caucasians who move from a northern climate to the equator will have darker skin. The mechanisms regulating their pigmentation do not change; rather the input to those mechanisms change, resulting in different outputs.

{| class="wikitable"
|-
! !! Adaptation !! Exaptation !! Byproduct !! Random variation
|-
| Definition || Organismic trait designed to solve an ancestral problem(s). Shows complexity, special "design", functionality || Adaptation that has been "re-purposed" to solve a different adaptive problem. || Byproduct of an adaptive mechanism with no current or ancestral function || Random variations in an adaptation or byproduct
|-
| Physiological example || Bones / Umbilical cord|| Small bones of the inner ear || White color of bones / Belly button || Bumps on the skull, convex or concave belly button shape
|-
| Psychological example || Toddlers' ability to learn to talk with minimal instruction || Voluntary attention || Ability to learn to read and write || Variations in verbal intelligence
|}

One of the tasks of evolutionary psychology is to identify which psychological traits are likely to be adaptations, byproducts or random variation. [[George C. Williams (biologist)|George C. Williams]] suggested that an "adaptation is a special and onerous concept that should only be used where it is really necessary."<ref>George C Williams, ''Adaptation and Natural Selection''. p. 4.</ref> As noted by Williams and others, adaptations can be identified by their improbable complexity, species universality, and adaptive functionality.