Comparative perspectives on human gender development and evolution

Abstract

Human behavioral sex differences are ubiquitous, but the degree to which these sex differences are evolved or culturally invented is hotly contested across disciplines. A review of the human research yields strong evidence that somatic and social causes are both important in human behavioral sex differentiation, but researchers in this area struggle to agree on the relative importance of each. Understanding the social and somatic determinants of nonhuman primate sex-typed development may shed light on the relative responsibility of social and somatic causes of human behavioral sex differentiation. A review of this research (and related research on the proximate drivers of nonhuman primate behavioral development more generally) indicates that primate behavioral sex differentiation is rooted in somatic causes, but that these are situated in and cannot be extricated from social influences. Overt gender socialization and phenomena such as gender performance seem to be uniquely human. Primate research using a dynamic systems theoretical approach to behavioral development has the greatest potential to further clarify the workings of human behavioral sex differentiation, and further primate research is indispensable for understanding the evolution of human sex-typed behavior. Yrbk Phys Anthropol 156: 2015. V C 2014American Association of Physical Anthropologists Socioecological theory predicts that males and females are likely to maximize their fitness via different behavioral strategies (Emlen and Oring, 1977). This can lead to the evolution of sex-typed behaviorsbehaviors that are stably associated with and are more commonly exhibited by one sex or the other (referred to as "sex-related" in Fausto-Sterling et al., 2012a). For example, on average, female spotted hyenas exhibit aggression more often than male spotted hyenas (Drea, 2009), and male chimpanzees exhibit more aggression than female chimpanzees (Watts, 2004). Increased aggression is a female-typed behavior in hyenas and a male-typed behavior in chimpanzees. Although both sexes of both species exhibit aggression, and although male and female distributions of this trait's expression might overlap, most researchers would agree that increased aggression in female hyenas and male chimpanzees relative to their opposite-sex counterparts has been driven by stronger positive selection for this trait in the more aggressive sex of each species (CluttonBrock et al., 2006).Humans exhibit a number of sex-typed behaviors, and these are often thought to be adaptive products of sexual selection. For example, male-typical advantage in threedimensional spatial skills has been attributed to selection for male hunting prowess (Joseph, 2000) and/or male-male fighting abilities (Geary, 1995), while femaletypical advantage in object location memory has been attributed to selection for female foraging efficacy (Eals and Silverman, 1994). However, humans are unique among animals in the degree to which culture directs behavior. Since hypotheses of the evolution versus encultu...

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