Archer argues that sexual selection is a more comprehensive explanation for sex differences in direct aggression than social role theory. We concur completely with this assessment. Indeed, we find it hard to believe that social role theory, even the “biosocial” version, retains any scientific credibility at all in the twenty-first century. To us, social role theory is a vestigial remnant of human exceptionalism. Given the overwhelming preponderance of comparative evidence for sexually selected sex differences in intraspecific aggression across such a broad diversity of species, it does great violence to the principle of parsimony to invent a special explanation for exactly the same phenomenon in our own species. Surely, such special pleading cannot be considered sound scientific theorizing.
Although we agree that sexual selection theory is essential for explaining sex differences in aggression, Archer seems indecisive regarding the relationship between sexual selection theory and the influence of social roles. Archer suggests that evolved dispositions typically do not rely on socialization practices that could vary from culture to culture (sect. 2.1.2). However, he acknowledges that several ecological and social conditions (e.g., scarcity of resources, operational sex ratio, and culture of honor) are predicted to modify the sex difference magnitude according to the sexual selection view. Here, Archer's argument would have been aided by emphasizing that evolved dispositions and the influence of social context are not in competition with one another. Further, Archer's analysis of intrasexual aggression would have been strengthened by specifying why the sexual selection theory of sex differences in aggression is consistent with epigenetic sensitivity to particular environmental conditions, rather than emphasizing insensitivity to those specified by social role theory. This emphasis becomes more difficult to understand in the light of the discussion of intersexual aggression in which sexual selection theory and social role theory are treated as complementary explanations. This leaves the reader confused about why parts of the social role explanation, or at least similar social conditions, could not be integrated with the sexual selection explanation.
The analysis would have been further strengthened by specifying the differences between the two theories at both the ultimate and proximate levels of explanation. Advocates on both sides of this debate should attempt to explicitly specify what their theories imply about both levels, because there is a tendency to contrast the ultimate level of sexual selection theory with the proximate level of social role theory. Although Archer does present proximate level mediators specified by each theory, it might have been helpful to examine what social role theory implicitly implies about the ultimate level. Each theory implies some differences at both levels, and an effort should be made to translate the two models into the language of each level to allow more thorough examination.
Archer acknowledges there is evidence for an association between “internalization of gender roles” and measures of aggression (sect. 2.9). However, in our own lab, we have found evidence that individual differences in both mating effort and life history (LH) strategy are associated with both sexual aggression (Gladden et al. Reference Gladden, Sisco and Figueredo2008) and negative androcentrism (bias against women; Figueredo et al., in preparation), suggesting that sexual selected LH strategies may account for the association between so-called gender roles and aggression. Future work should attempt to put the sexual selection and social role models in direct competition. The use of path-analytic modeling may suggest which model fits the data best.
Although Archer's primary point was to discuss sex differences in physical aggression, we would suggest that expanding a discussion of sex differences in indirect aggression could have strengthened his argument that sexual selection plays an important role in determining both between and within sex differences in aggression. The difference between males and females in indirect aggression may not be as substantial as that of physical aggression; however, the evidence he presents on effect size clearly indicates that indirect aggression is employed more by females than by males (sect. 2.8). Why is this? Archer's use of sexual selection theory for explaining sex differences in physical aggression could be applied equally well for examining sex differences in indirect aggression. The following are just a few examples of how this logic could be applied.
Archer suggests that, “Overall, the most likely prediction from a sexual selection perspective is an early emergence of sex differences in aggression combined with a peak in risky competition during young adulthood” (sect. 2.1.2, para. 3). One could make the same prediction focusing on indirect rather than physical aggression. More specifically, one could predict the following: (1) females will begin engaging in indirect aggression at an early age (e.g., grade-school girls negotiating social networks at recess), and (2) female indirect aggression will increase into adolescence and young adulthood (e.g., junior-high girls gossiping about rivals at lunch).
Archer also addresses context and within-sex competition, “Sexual selection predicts variability in response to conditions that affect the extent of inter-male or inter-female competition, notably resources that are important for reproduction, such as access to mates, and the status and resources important in this process” (sect. 2.8, para. 1). The same logic could be used to further predict differences in indirect aggression among females. For example, one could predict that: (1) there should be less indirect aggression from females who have formed satisfactory and relatively secure long-term pair bonds or secured adequate resources; (2) there should be more indirect aggression from females who pursue short-term mating strategies (fast LH strategy) and less indirect aggression from females who pursue long-term mating strategies (slow LH strategy), especially once a secure pair bond is established (i.e., the less secure the bond, the more incidents of indirect aggression); and (3) female indirect aggression should focus on issues of contested resources, relative fertility, and paternity certainty.
In short, Archer misses several opportunities for putting the theoretical predictions made by both himself and others into direct competition in a way that would further the interests of strong inference (Platt Reference Platt1964). Hence, although essentially correct, in our view his critique did not go far enough in demolishing the antiquated and obsolete alternative hypotheses reviewed.
