With Eugene's assistance, I have attempted to link all of these related posts together. We'll see if I have been successful.

My last post discussed some average psychological differences between the sexes. This post will discuss potential effects of these and other differences.

The "free rider" problem is potentially huge in combat. It is entirely rational from a selfish perspective for a soldier to keep his head down out of the belief that any minuscule effect that his battlefield actions might have on the outcome of the battle is far outweighed by the potential loss of his life. What really needs to be explained is not the fact that there are free riders but rather that there are so few of them. The explanation lies, in part, in the fears and motivations of soldiers.

Men going into combat for the first time face an array of fears. Among them, of course, are the fear of being killed or seriously injured. Some commentators have also identified a fear of killing, although it's not clear that "fear" is the proper word to describe the reluctance to kill often exhibited by western soldiers.

These fears -- fear of death, fear of injury, and fear (or at least reluctance) to kill -- are negatively motivating, and they are likely to affect men and women differently. Women's greater fear of death and injury and greater aversion to physical risks are likely to affect their combat performance negatively. Just being in a war zone is considerably more stressful to women than to men. A study of male and female support troops in the Gulf War, none of whom had seen combat, found that women reported significantly more psychological stress than men, especially stress in anticipation of combat.

Empathy also has negative effects, as it not only engenders a reluctance to kill but is also associated with greater guilt for having killed. Some reports coming back from Iraq suggest that women are suffering higher levels, and a more severe form, of PTSD than men are.

Perhaps surprisingly, fear of injury and of death are not the greatest fears that soldiers face going into battle (especially for the first time). A recurrent feature of military memoirs is that fear of cowardice dwarfed the fear of injury and death. As Samuel Stouffer's study of the American soldier in World War II found, showing cowardice in battle brought not just censure for cowardice itself; even more powerfully, "to fail to measure up as a soldier in courage and endurance was to risk the charge of not being a man." The fear of not measuring up as a man is highly motivating, but it is not one that motivates women.

In thinking about the relative suitability of the sexes for combat, one might think about real-life situations in which individuals have a choice whether to engage in activities that involve a combination of relevant traits -- such as fear, risk-taking, and physical aggressiveness. For example, who are the people who foil robberies, chase down purse snatchers and carjackers, and rescue others from criminal assaults? The answer is that these people are overwhelmingly men.

Combat Courage and "Defining Bravery Down"

If one of the primary motivators of men in combat is the need to prove their manhood and the need to maintain the respect of their comrades, one must ask what motivates women in combat? Surely, it is not the need to prove their manhood (or their womanhood, for that matter). As for respect of their comrades, women can maintain it at a much lower level of courage than men can, a fact that has substantial implications for the level of combat courage that one might expect to see from both women and men.

Aristotle wrote that "a man would be thought a coward if he had no more courage than a courageous woman." That may seem a gratuitously chauvinistic comment, but it captures an important truth. How often does one even hear of a woman referred to as a coward? The dictionary defines "cowardice" as "disgraceful fear or timidity." We do not decline to label women cowards because women do not display fear or timidity. Instead, we do so because we do not find women's fear or timidity disgraceful in settings in which we would see disgrace in men.

Because of the strong norms of equality in combat groups, if lesser courage is expected -- or at least accepted -- from women, that fact is likely to define bravery down for all. In his book "Hero or Coward," German military analyst Elmar Dinter observed:

We should never forget that the average soldier would really like to run away from the fighting. The group prevents him from doing this. If group morality allows for an "honourable" means of flight, it will be accepted gratefully.

Exactly this dynamic may have been in play in 2004 when a mixed-sex platoon of reservists refused a direct order to drive a fuel convoy, although the Army's reticence about the incident compels one to rely on (perhaps unfair) speculation. The reservists argued that it was a "suicide mission" because their trucks were not armored. News reports did not indicate who the ringleaders of the mutiny were, although it came to light when a female specialist left a message on her mother's voice mail asking her to "raise pure hell."

One could easily see how the sex composition of the group could have contributed to the incident. Expressions of unwillingness by female soldiers would give cover to the men to go along. By supporting the women who did not want to take on the mission (if that is what happened), the male soldiers could convert in their minds a cowardly refusal to take on a dangerous mission into a brave -- even honorable -- willingness to accept discipline to "protect" the women. The mission may be aborted, but honor within the group would be preserved.

Even if women actually were as courageous as men, they are not expected to be. That lower expectation of their courage -- irrespective of their actual levels of courage -- would almost inevitably result in reduced combat performance.

My next post will discuss the effect of sexual integration on cohesion and trust.