By Robert Roy Britt, LiveScience Managing Editor
posted: 10 May 2006 09:13 am ET
Buzz up!
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While it is tough to be a woman, being a man can be downright
deadly.
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.
Butting heads
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.