The role of evolutionary hypotheses in psychological research: Instincts, affordances, and relic sex differences

Properly formed and properly used evolutionary hypotheses invalidate most common criticisms and must be judged, like other hypotheses in science, through their ability to be theoretically and empirically progressive. Well-formed hypotheses incorporate established evolutionary theory with evidence of actual historical conditions. A complex, multifaceted hypothesis can predict patterns of phenotypic variation that would make sense if the hypothesis is true, but be unlikely if it is false. This approach to evolutionarily guided research is illustrated via the sexual-dinichism hypothesis, which proposes historical niche divergence between the sexes during which females could still make adaptive use of trees, but larger males could not. This has led to the investigation of several traits in modern children, where evidence for predicted sex differences in behavior were discovered. We find the objections of critics (e.g., Burton, this issue) to be appropriate for criticizing post hoc evolutionary explanations and perhaps poorly developed hypotheses, but not well-formed and properly used theories. We hold that evolutionary theories are an essential part of psychology in general and ecological psychology in particular.