It's not easy being male. Research shows men are naturally programmed to check out early — at least sooner than women.
Recent analysis by researchers at the University of Michigan showed that three men die for every woman during the years between adolescence and adulthood. In the broader view, 16 men die for every 10 women before the age of 50.
What's so hazardous about being male? Researchers believe it ultimately has to do with early programming and the other sex, or, rather, pursuit of them.
"There's a reason why there are societal expectations for men to be tough," said Daniel Kruger, a social psychologist at the University of Michigan Institute for Social Research and lead author of the study appearing in a recent issue of Evolutionary Psychology. "What happens is the behavioral tendencies that we're selected for in early history is still with us today."
Here's the idea: When it comes to reproduction, female mammals (including women) make a huge physical investment. Being pregnant consumes calories and energy that would normally be used for self survival. Then there is the danger that mothers face during childbirth and the costs of caring for young after they're born (for most mammals the mother is the primary caregiver).
Males, on the other hand, have minimal costs when it comes to reproducing. Because the cost is relatively low, males typically try and mate as much as possible. The trick, then, lies in convincing females to mate and this means beating out other males for the role. That means being aggressive and doing things that may not be great for personal survival, but helps gain status and win female attention.
"Basically the idea is men front end all their risk because it's important to reproduce early and often," said Benjamin Campbell, an expert in anthropology at Boston University.
Times have changed, of course, at least for humans living in developed countries. Childbirth isn't nearly as risky as it once was. Many men play equal roles in taking care of children and most men don't father children of several women.
Nonetheless, Kruger says behavior stemming from early man's dog-eat-dog days remains in our systems. And that's bad news for men. Kruger figures more than 375,000 lives would be saved each year in the United States if men's risk of dying were as low as women's.
"You see a greater tendency for risky behavior among men," said Kruger. "Men are predominantly the ones getting themselves into trouble."
Using data from the National Center for Health Statistics, the World Health Organization and the Human Mortality Database, Kruger and his University of Michigan colleague, Randolph Nesse, showed that men had higher death rates than women for all 11 leading causes of death in the United States.
The difference between male and female deaths peaks during young adulthood from ages 20 to 24, when three times as many men die as women. Among causes of death, the biggest differences between male and female mortality rates were for suicide, then homicide, followed by non-automobile accidents and then automobile accidents.
"You would think the peak would be among teenagers when testosterone levels are rising rapidly," said Campbell. "The fact that it peaks during young adulthood suggests it might be directly related to competition for females."
One might also expect death rates for the sexes to even out later in life when reproduction is less of an issue. But, in fact, the second peak in differences in mortality rates occurs later in life when men and women reach their 60s. At this point men are 1.68 times as likely to die as women.
This is partly due to higher suicide rates. Kruger suspects that men and women may attempt suicide at fairly equal rates, but men choose more violent and, therefore, more effective means.
But the main male killer among the 60-75 age group is disease.
Blame Your Hormones
Kruger says men may be taking greater risks in their general health care (as in eating too many cheese steaks, smoking and drinking too many six-packs) that makes them more vulnerable to disease later in life. But it could also be due to a factor beyond men's control. Studies show that testosterone — the hormone that promotes aggressive, competitive behavior — also plays a role in suppressing the immune system.
Long-term comparisons between castrated and intact men show that castrated men outlive other men by up to 15 years. The subjects in these comparisons were incarcerated, and less vulnerable to violent deaths, but the leading cause of the elevated rate of mortality among intact males was infectious diseases.
The same appears to be true among general populations. Surveys show that infection or parasites kill twice as many men than women in developed countries and four times as many in undeveloped countries.
Theories suggest that evolution designed men to expend more energy on fighting other males than fighting disease. This may have placed them at higher risk, but winning more females may have been a worthwhile tradeoff.
Kruger points out that the tradeoff doesn't make as much sense today, especially considering that brute strength is now less of a factor when it comes to fighting. Technology like guns and fast cars has made killing and getting killed much easier. That means a little aggression goes a long way.
All in all, the numbers suggest that evolutionary behavior doesn't always work well for men in modern times and that, argues Kruger, merits some attention.
"There has been a big push in the last decade for women's health," he says. "Maybe it's time now to push for men's health issues too."