Male life span tied to mate competition


If you've ever felt sorry for a man who had a lot of competition in the singles dating scene, there may be more reason to worry about him than his seemingly bad luck in getting a date.

"Men who reached their sexual maturity in an environment with higher sex ratios (i.e., higher proportions of reproductively ready men) appeared to suffer higher long-term mortality risks than those in an environment with lower sex ratios," wrote a group of researchers who were concerned enough about these guys to look into the situation.

That's fancy talk to say that men who have fewer women to choose from when they're at their sexual peak and looking for a mate live, on average, three months less than men who don't have as much competition from other men for a woman's affections.

Results of the study (pdf) are in this month's issue of the journal Demography, published by a professional organization made up of people whose focus is the statistical science of human populations.

Three months doesn't sound like a lot to me. From where I sit, the more pressing issue is the fact that women outnumber men in most settings, unless you live in Alaska or Wyoming, you're deployed in the military or you make your living drilling for oil.

But I digress.

"Three months is in the ballpark of what you'd expect," said Dr. Nicholas Christakis, senior author on the study and professor of medicine and medical sociology at Harvard University.

Christakis said he and his colleagues didn't expect to find that people suddenly dropped dead because of being single -- or marrying late. But three fewer months of life is relative.

"The [gender] ratio is not something that an individual [usually] controls," he said. "We thought therefore that we would study the circumstances in which some marry and others don't, not through forces of their own."

Christakis collaborated with sociologists from the Chinese University of Hong Kong, the University of Wisconsin and Northwestern University on the study, paid for by the National Institutes of Health and the Robert Wood Johnson Foundation.

They studied two sets of data. The Wisconsin Longitudinal Study provided information on more than 4,100 men who were tracked for 50 years, from the time they graduated from Wisconsin high schools in 1957.

The researchers also compared Medicare claims data with U.S. Census Bureau information for a complete national sample of more than 7 million men.

The only reason the researchers didn't look at how women fared when they outnumbered men was because census data wasn't available.

Decades-long preferences of families for sons over daughters in China, India and other countries with significant gender imbalances have created concerns about the rise in violence against women and overall political unrest.

The study, however, shows that skewed gender ratios could also mean bad news for men.

"We're showing that [imbalance] could also harm the men themselves," Christakis said. "What this shows is that social factors affect us. We literally come to embody the social world around us."

The study didn't set out to specifically answer the reasons for the effect on a man's longevity.

"The relative lack of members of the opposite sex may be stressful for them and induce biological changes in gene regulation called epigenetics," Christakis said. "It may mark them for life."

In other words, the psychological effects of having to compete for a woman in the prime of one's life -- and whether or not a guy ever finds "the one" -- may take the ultimate toll.