 Many attempts to establish the influence of culture in shaping behavioral and psychological diversity take the form of arguments from exclusion, aimed at ruling out other candidate explanations that might account for the specific pattern of intergroup variation in question. Competing explanations can take numerous forms. For example, until the 1950s many instances of behavioral variation were thought to be attributable to genetic differences between human groups (Barkan 1992). Research in the life sciences over the last 70 years, however, failed to produce evidence to support such explanations, finding instead that biological differences between human populations are minor and superficial (Hirschman 2004). The loss of confidence in purely genetic explanations inspired researchers to continue exploring alternatives.