Human nature or human natures?

Most evolutionary psychologists share a belief in one key concept: the environment of evolutionary adaptedness (EEA), i.e., the ancestral environment that shaped the heritable mental and behavioral traits of present-day humans. It is usually placed in the African savannah of the Pleistocene, long before our ancestors began to spread to other continents some fifty thousand years ago. Thus, later environments have not given rise to new traits through genetic evolution. This belief rests on two arguments: 1) such traits are complex and therefore evolve too slowly to have substantially changed over the past fifty thousand years; 2) because the same time frame has seen our species diversify into many environments, recent traits should tend to be environment-specific and hence population-specific, yet such specificity seems inconsistent with the high genetic overlap among human populations. Both arguments are weaker than they seem. New complex traits can arise over a relatively short time through additions, deletions, or modifications to existing complex traits, and genetic overlap can be considerable even between species that are morphologically, behaviorally, and physiologically distinct. There is thus no conceptual barrier to the existence of EEAs in post-Pleistocene times. Such a paradigm could shed light on such research topics as the visual word form area, reproductive strategy, predisposition to violence among young men, and personality traits. Eventually, a multi-EEA model may dominate evolutionary psychology, perhaps after an interim period of accommodation with the current model. (C) 2011 Elsevier Ltd. All rights reserved.