Women live longer than men. And now scientists suggest a simple Darwinian reason: Competing for a mate can wear a guy out or get him killed.
“Women live longer in almost every country, and the sex difference in lifespan has been recognized since at least the mid-18th century,” said Daniel Kruger at the University of Michigan. “It isn’t a recent trend; it originates from our deep evolutionary history.”
The idea is presented in the spring edition of the journal Human Nature.
In common chimpanzees, Kruger and his colleague Randolph Nesse report, mortality spikes among males around age 13, just as they’re old enough to breed and start competing for social status.
Males of many species must fight vigorously for the right to mate. Think of rams butting heads. Spectacular male bird plumage is another example of biological effort required to succeed, effort that uses energy and can shorten a life.
In this scheme of natural selection, evolution shapes traits that help the best genes survive, sometimes to the detriment of individuals.
Human males don’t always have to wrestle to get a woman these days, but the pressure to succeed sexually hasn’t changed much, the researchers argue. Only the methods have been revised.
Drop your club
Though society may be changing dramatically even from this generation compared to the last, some things never change. Women still have to bear the greatest burden of raising a family—giving birth—and often take on more of the day-to-day responsibilities for the ensuing 18 years. So just as in ancient times, they remain very choosy in selecting a mate.
Now, if you buy all this logic, here’s the critical part: To impress women, men remain prone to risky behavior, just as they have been for millennia and just as other male animals are.
In caveman days, being good with a club was one way to get a mate. Now, the ability to purchase a blinged-out SUV has similar value, the scientists suggest.
“Men compete for resources and social status, which are criteria men are valued for in mate selection,” Kruger told LiveScience.
Own worst enemy
The pressures of mate selection might be most intense for those just coming into adulthood. And likewise the recklessness of youth, as previous researchers have suggested, is a foundation for human social systems. Young men form the front lines in wars, for example.
One old study on the topic put it this way: “Lacking the opportunity for warfare, some [young adult men] will find other ways to place their lives at risk.”
Another study last year, reported in the Journal of Epidemiology and Community Health, reached similar conclusions. It cited “excessive risk taking, aggression, and the suppression of emotions by boys and young men” as being directly related to lower life expectancy in men.
Among the not-so-beneficial behaviors this includes are smoking, reckless driving and violence, Kruger and Nesse write. This idea is reinforced by data that show low social status has a greater impact on male mortality rates than on those of women: Men of lower status or who lack a mate are more likely to engage in a riskier pattern of behaviors, Kruger said.