"You generally expect to see support for the president as commander in chief and for the war, but this is a different kind of war than those we've fought in the past, particularly for families," said David Segal, a military sociologist at the University of Maryland. Today's all-volunteer force is older and more married than any before it. Facing a shortage of troops, the Army increased the maximum enlistment age from 35 to 42 and called up reservists, who tend to be older and more settled than recruits fresh out of high school. The result is a fighting force that left thousands of spouses and children behind.

And among those families with soldiers, sailors and Marines who have served in Iraq or Afghanistan, 60% say that the war in Iraq was not worth the cost, the same result as all adults surveyed.

One branch of evolutionary psychology focuses on the distinct mating preferences and strategies of men and women. For example, because our male ancestors were easily able to sire numerous children at little cost to their fitness, the theory says, they were inclined to short-term mating with multiple partners. In choosing mates, they gravitated toward youth and physical attractiveness — markers of fertility and health. By contrast, females, for whom conception meant pregnancy and the need to care for a child, were more selective, searching for long-term commitments from males with the resources and willingness to invest in them and their offspring.