I agree with Archer that “Social roles … have their ultimate origins in evolutionary history” (target article, sect. 5, last para.) and think that the difference in levels of explanation between evolutionary theory and social role theory is responsible for some of the confusion surrounding this debate. Archer's review of these theories as they apply to sex differences in same-sex aggression is very helpful, but a few of the evolutionary predictions raise additional questions.
Most of Archer's evolutionary predictions regarding same-sex conflict are clear, but two are puzzling. One is the claim that evolutionary theory predicts the early emergence of sex differences in direct aggression. If this is a sexually selected trait, why should it appear before it is needed in mating competition? Most sexually selected traits appear at puberty, so an additional argument is required to support this prediction.
Also puzzling is Archer's assertion that evolutionary theory would not predict a sex difference in anger. Emotions motivate behavior and are affected by selection only if they affect behavior. If theory predicts a sex difference in aggressive behavior, why would it not also predict a sex difference in the emotion that motivates it?
The answer may help us understand the evolutionary reasons for greater male same-sex aggression. As Archer notes, two arguments have been proposed: (1) greater benefit to males because of greater variance in male reproductive success (the usual argument), and (2) greater cost to females, due to their greater parental investment (Campbell Reference Campbell1999). If the first of these is driving sex differences in aggression, we should expect reduced anger in women, to motivate their less intense aggressive competition. The second argument, in contrast, would predict equally intense competition but would temper anger with fear, thereby leading to less costly, but not less emotionally-intense, forms of aggression. This seems more consistent with the data showing that women and men experience similar degrees of anger, although they may express it differently.
My chief concern with this otherwise valuable target article lies in its treatment of partner violence. Evolutionary theory provides a robust explanation for the finding that males are more likely to control sexual access to females than the converse, and often use aggression to enforce it. In view of this, Archer's claim that there is no sex difference in spousal abuse in Western nations is surprising and deserves another look. The claim of sexual symmetry ignores much contradictory evidence, ignores sex differences in motive, and relies heavily on studies using the problematic (Dobosh et al. 1992) Conflict Tactics Scale (CTS). Johnson (Reference Johnson2006) has shown that violence involving proprietariness and control (“intimate terrorism”) is heavily male-biased, unlike the disputes picked up by the CTS, which arise chiefly from conflicts of daily life (“situational couple violence”). The former also causes far more harm, both physically and psychologically, than more sexually symmetrical altercations (Johnson & Leone Reference Johnson and Leone2005). Evolutionary theory that addresses male sexual proprietariness and concern over cuckoldry provides a phylogenetically broad explanation for this more serious type of male-biased violence, and leads to predictions that distinguish it from violence arising from conflicts of interest in other domains (Daly & Wilson Reference Daly and Wilson1988; Wilson & Daly Reference Wilson and Daly1996).
