 Most of the alternative explanations that are not cultural in the sense at issue here—and so which do not give a central role to social transmission—attempt to explain intergroup variation by stressing the importance of differences in the external physical or ecological environments inhabited by different groups, or by appeal to the operation of psychological mechanisms like causal reasoning or individual trial-and-error learning (Richerson &amp; Boyd 2005). The range of options can be elucidated by examining evolutionary approaches to human behavior, and comparing the distinct way each approach appeals to such factors in their proprietary modes of explanation (E. Smith 2000). For example, human behavioral ecology remains largely agnostic, or at least assigns little significance to, the character of the internal psychological mechanisms that might lead to group level behavioral diversity. Instead, behavioral ecologists appear to simply assume (perhaps unrealistically, see Driscoll 2009) that humans are able to produce behavior that optimizes fitness across a wide range of environments, and by implication also assume that individual human minds are generally flexible enough to calibrate behavioral strategies to best fit whatever ecological circumstances they find themselves in (Grafen 1984). On this view, patterns of behavior within a group typically reflect commonalities in the ecological circumstances faced by most members of the group, and differences in the patterns found between groups reflect, fairly directly, differences in the ecological circumstances those groups inhabit. Such explanations make little mention of mental structure and no mention of culture or cultural inheritance.