Men evolved willing to risk death for sex, partly explaining why men die faster than women in virtually every country worldwide.

But monogamy and economic equality could counteract this trend — by assuring men they are likely to get some loving, a new study suggests.

The study was published in the current issue of the journal Evolutionary Psychology.

Willing to risk it all for sex (and kids)

"The name of the game in evolution is to get your genes in the next generation," said study researcher Daniel Kruger of the University of Michigan.

Reproductively speaking, men have more to gain, and less to lose, from risk-taking behavior than women, researchers have long said. Essentially, it's okay if the guy dies, because at least once he's done the initial deed, there a chance his offspring will survive.

While having an involved father increases the odds of a child's social and reproductive success, not having a mother, even if she disappears after weaning, is often fatal, especially in developing countries, several studies have shown. Therefore, women, unlike men, may have evolved to avoid physical risks, theorizes researcher Anne Campbell of Durham University in England who was not involved with the study.

Men, meanwhile, are busy trying to impress women, especially pretty women, by taking the risks women avoid.

Men know, at least subconsciously, that women, because of their greater physical investment in childbearing and rearing, are most receptive to men who seem like good providers — outwardly denoted by "status and stuff," Kruger said.

And throughout evolution, men have used violence, shows of physical prowess and other forms of risk-taking to not only acquire status and stuff, but to advertise it. These tactics (in addition to flashing platinum credit cards and jousting with verbal taunts) continue to be instinctually used by today's men to one-up one another and attract women.

Assessing the competition

These risky flaunts, and so male life span, could be affected by economic circumstances, Kruger figured. Comparing 70 countries, he looked at cultural factors that likely exacerbate sexual competition among men. He found that economic inequality and acceptance of male promiscuity disproportionately affected the life spans of men, while women were comparatively immune.

In countries like Norway, that are relatively egalitarian, male mortality rates are more equal to those of women, with a difference of 4.5 years on average. But in countries like Columbia and, to a lesser extent, the United States, where there are more significant differences between the rich and the poor, men out-die women faster, in part because they are competing — either violently or stressfully — for status, stuff and, ultimately, sex, Kruger said. The lives of men in Columbia and the United States are on average shorter than their female counterparts by 7.8 and 5.2 years, respectively.

Even fictional economic inequality may have an effect on male life span. "Status-conscious networks — like MTV or whatnot — show a lot of affluence," Kruger said. "People look at that and think, 'Oh wait, that is what I should have, too.' Their expectations go up." And then the striving and competition intensifies.

Acceptance of polygyny — one man mating with many women — also correlates with male mortality rates. Polygyny means one dude can impregnate many gals, leaving men lower on the totem poll with fewer opportunities to have their own children. This makes the benefits of rising to the top of the hierarchy that much greater — and makes the risk of injury, and even death, seem relatively inconsequential.

Other studies have suggested that men who are not looking for sexual conquests, presumably either because they are happily mated or otherwise distracted, are less likely to engage in risk-taking behavior.

In all, the research suggests that monogamous, egalitarian societies would do a lot for a man's life span, Kruger said.

"And just about all men could benefit from taking a step back from working ourselves to the bone, trying to keep up with the Joneses," Kruger said. It may be an instinctual drive, but it doesn't necessarily benefit one's quality of life.

And it may even shorten it.