Many of the issues raised in the comments were thoroughly explored in the give-and-take there, so I will respond only to a few comments.

Several comments dealt with the issue of endurance, and it is an important one. One commenter cited a study purporting to show a female advantage at ultra-long distances. I do not have a copy of the article cited (my university's electronic subscription to that journal begins in 1998), but the abstract indicates that men and women were matched for "56 km race time, age and training." But matching for speed and training (presumably meaning aerobic capacity) means that the most fit women would be compared against less fit men. That is, if you take the top woman in terms of speed and aerobic capacity, you would compare her not to the top man but rather to a man who had the same speed and aerobic capacity as the top woman, who would generally be quite a distance from the top man.

The difference between being able to perform a task and being able to perform it over and over again (someone mentioned repeated combat sorties) can be very important in combat. That is the reason that women in the Israeli Defense Force are not eligible for combat assignments in the Armored Corps even though they do serve as tank instructors. Experience showed that the women could not load shells over sustained periods of time, which they do not have to do as instructors but may have to do in combat.

Several commenters remarked on the story about strength and the EP-3E pilot's experience over the South China Sea. The point of that story was not that all military planes present equivalent strength demands but that strength demands can crop up when things go wrong, even if a job does not require strength when things go right (which is the same point made about the USS Samuel B. Roberts). Moreover, no matter how high-tech the aircraft, once you are shot down, you are essentially an under-armed infantryman whose obligations are to survive (and assist fellow crew members in doing so, perhaps by dragging them from the wreckage), evade pursuers, resist potential captors, and escape from captivity. The harrowing stories of many shot-down pilots suggest that physical fitness and strength can make the difference between freedom and captivity and between life and death.

The post concerning psychological sex differences drew very animated responses. Let me just say a little bit to clarify the point that I was making. When talking about physical sex differences, my point was that they are relatively easy to measure but there is not much overlap between the sexes. If that were the only issue raised by sexual integration, the sensible thing would be simply to provide sex-neutral tests of physical capacity and let the chips fall where they may -- which would result in only a small number of women being deemed eligible for combat (and probably pressure for "gender-norming," as well).

When talking about psychological sex differences related to combat, there is more overlap but these differences are also more difficult to measure. There are various psychological tests to measure such things as physical aggressiveness and risk-taking, and these tests routinely show substantial differences between men and women. Most authorities on combat behavior would agree that physical aggressiveness and willingness to take physical risks (not suicidal recklessness as some commenters suggested) are associated with combat effectiveness. If you look at settings in which differences in aggressiveness and risk-taking have real-life consequences -- that is, when people are actually risking their lives, whether for heroic or criminal purposes -- you see a much greater sex difference in actual behavior than is revealed by psychological testing.

Ideally, again, one would select just those individuals who have the mix of psychological traits that allows them to overcome fear in the face of mortal danger, to be willing to take the fight to the enemy if the mission demands it -- risking their lives in the process -- and to inflict lethal violence on the enemy when the situation calls for it. I'd be surprised to hear that anyone -- even the most ardent supporter of sexual integration -- believes that this description fits men and women equally.

That's where the lack of predictability comes in. It is a staple of the combat-behavior literature that it is often a surprise who turns out to be an effective fighter (and who doesn't). Because some people do very well in training but bomb out in actual combat, you can't count on training to weed out those who won't do well. If you believe that there is a substantially higher proportion of Xs in Group 1 than Group 2, but you cannot identify which ones are the Xs, it is rational to attempt to maximize the number of Xs by selecting from Group 1 rather than from Group 2.

One or more of the commenters made the valid point that women who want to serve in the combat arms are not going to be the "average woman." That is true, but the men who serve in the combat arms are also not "average men." There will be a selection bias operating in both groups, although no doubt the female combat volunteer would deviate more from the female average than the male combat volunteer would from the male average.

One of the problems with spreading my blog entries out over the course of a week is that it is tempting to conclude that each posting is claimed to present a sufficient reason -- standing alone -- to exclude women from combat. What I tried to do in my book, and what I hope to do with the posts on this blog taken as a whole, is to identify a number of difficulties presented by integration of women into combat roles. The ultimate question is whether the combined effect of these difficulties would predictably lead to a less-effective military.