The choice between the evolutionary approach advocated in the target article and the biosocial approach that it criticizes, is an important one that is of more than academic interest. In fact, it has direct application to a critical policy choice facing modern governments: whether women should be integrated into military combat units.

A variety of sex differences are relevant to the integration question. Most obvious are differences in physical attributes – such as size, strength, speed, and endurance – which overwhelming evidence shows are primarily a consequence of sex hormones (Cheuvront et al. Reference Cheuvront, Moffatt, DeRuisseau, Wolinksy and Driskell2002). Differences in intragroup interactions between all-male and sexually integrated groups also bear on the question of integration, as issues of group cohesion, sexual relationships, male protectiveness toward women, among others, are of central importance (Browne Reference Browne2001; Reference Browne2007). Of specific relevance to the subject of the target article are sex differences in aggressiveness and physical risk-taking.

The biosocial theory attributes sex differences in aggressiveness and risk-taking to “the distribution of women and men into different specific roles in societies” (Becker & Eagly Reference Becker and Eagly2004). Characteristics such as a propensity to engage in risky behavior are imputed to men because men are more likely to occupy roles requiring such action due to their greater physical prowess and the restrictions that childbearing places on the activities of women.

A critical flaw in the biosocial theory is the lack of curiosity it exhibits over the origins of physical sex differences. The theory assumes that the evolutionary forces that left their imprint on human bodies had no similar effect on human minds, an assumption that is untenable if one reflects on where these physical differences came from. Because these differences are consistent with a common mammalian pattern – according to which sexual size dimorphism appears to be an evolved consequence of male-male competition that has behavioral correlates – the principle of parsimony would, at least as a first cut, suggest common origins. Needless to say, a social-role explanation for behavioral sex differences throughout the mammal world is difficult to credit.

If men exhibit greater aggressiveness and risk-taking simply because they have been placed in roles that demand, or at least reward, these attributes, then one might expect that placing women into the role of combat soldier will cause them to exhibit the same kinds of aggressiveness and risk-taking as male soldiers. Because women have not widely served in combat, there is no clear empirical evidence directly on point. However, there are some data to show that even female soldiers respond differently to combat risks than men do.

A number of press reports from Iraq suggest that female soldiers are at least perceived as less aggressive than their male comrades. One story (in The Times of London), for example, described a female U. S. Army helicopter pilot who requested that the reporter use the term “neutralise,” rather than “kill,” because she did not want to create an erroneous impression that soldiers enjoyed killing. The reporter noted that “her sensitivity stands out in an army in which male soldiers talk of ‘smoking,’ ‘wasting,’ or ‘whacking’ the enemy” (Meo Reference Meo2006, p. 46). Another newspaper story (in the Washington Post) profiled a different female helicopter pilot who objected to the bellicosity of her male comrades: “Everyone was like, ‘Yeah, get them’ and I was having trouble with that really aggressive attitude” (Tyson Reference Tyson2005, p. A-1). According to a Chicago Sun-Times article, a female National Guard gunner noted that women do not fire their weapons as much as men do because of their greater caution. She continued:

I concede these are anecdotal accounts and are not necessarily representative. However, there is little reason to believe that they present a false picture.

Mere presence in a war zone is considerably more stressful to women than to men. Among male and female soldiers serving in non-combat positions during the Gulf War, women reported experiencing significantly more psychological stress than men, especially stress in anticipation of combat (Rosen et al. Reference Rosen, Wright, Marlowe, Bartone and Gifford1999). Reports from Iraq indicate that women are suffering post-traumatic stress disorder at approximately twice the rate of men, and suffering from more severe forms, despite the fact that women are exposed to considerably less combat danger (Scharnberg Reference Scharnberg2005, p. C-1). These reports are consistent with the view articulated in the target article that women exhibit higher fear levels than men.

The target article notes that studies typically find no sex difference in anger. However, there are sex differences in the correlates of anger that are likely to facilitate physically aggressive behavior in men and to be of importance in combat. Fessler et al. (Reference Fessler, Pillsworth and Flamson2004) have shown that anger increases risk-taking among men but does not do so for women. On the other hand, disgust inhibits risk-taking among women but not among men. Because the battlefield provides ample opportunity for both anger and disgust to operate, patterned differences between men and women in combat performance are predictable.

Average differences between the sexes are not necessarily a reason to exclude women from combat. In theory, soldiers could be selected based upon their individual attributes, including aggressiveness and risk-taking. One problem is that, as the target article notes, sex differences in naturalistic settings are generally greater than those exhibited in labs and on paper-and-pencil tests. Moreover, unlike strength, which can be easily and cheaply screened for, future courage under fire cannot be readily measured. A consistent theme in the combat-behavior literature is that one never knows who is going to be an effective soldier until the shooting starts, and the identity of the good fighters often turns out to be a surprise (Braun et al. Reference Braun, Wiegand, Aschenbrenner, Gal and Mangelsdorff1991; Browne Reference Browne2007, p. 111).

The question of whether to integrate the sexes in combat forces is an important one, with many lives potentially hanging in the balance. Knowledge of the origins of sex differences in aggression and risk-taking does not by itself determine appropriate military manpower policy. However, any policy adopted is more likely to succeed if it is grounded in accurate factual assumptions.