A new study across 20 countries reveals for the first time just how much bigger the risk of premature death is for men than women, whatever their age. In the US in 1998, for example, men up to the age of 50 were on average twice as likely as women to keel over, and the risk remained greater even for those men who had made it to their eighties and beyond. Less surprisingly, the discrepancy in death rates between men and women was most extreme between the ages of 20 and 24, when three times as many men die as women. "Being male is now the single largest demographic factor for early death," says Randolph Nesse of the University of Michigan in Ann Arbor.
Nesse says that the finding has important implications for public health. "If you could make male mortality rates the same as female rates, you would do more good than curing cancer," he says. Nesse's colleague Daniel Kruger estimates that over 375,000 lives would be saved in a single year in the US if men's risk of dying was as low as women's.
The US data is backed by death rates in countries including Ireland, Australia, Russia, Singapore and El Salvador. Nesse and Kruger found that everywhere they looked, it's more perilous to be male. In Colombia for example, men in their early twenties are five times as likely to die as women of the same age.
Even more surprisingly, the pattern holds for every major cause of death, from car crashes to heart disease to homicide. For external causes of death, such as accidents, the difference between the sexes is greatest for young adults. But the second largest disparity between men and women in the US occurs when they reach their sixties. At that point in their life, men are 1.68 times as likely to die as women, mainly due to disease.
The gender gap has widened dramatically in recent years, but it has been on the rise since the 1940s, at least in the US, France, Japan and Sweden, where historical figures are available. The researchers suggest a number of factors that could be to blame for the trend. Population growth and globetrotting have led to a rise in infectious diseases. And improvements in public health and medicine may have benefited women more than men: for instance, far fewer women now die at a relatively young age during childbirth. Technological advances may have played a part, too, by supplying men with more powerful guns and ever faster cars.
Nesse and Kruger say that sexual selection could also partly explain some of the differences. Men generally invest less in their children than women do, and as a result may compete more vigorously with each other for potential mates. This rivalry could be what drives them to take greater risks, with the result that men have evolved greater reproductive success at the expense of longevity. The same may be true for chimpanzees and even fruit flies, says Nesse.
Betsy Mason reports from the Animal Behavior Society meeting in
Bloomington, Indiana, 13 to 17 July
Coverage of other scientific meetings is at
www.newscientist.com/conferences
New Scientist issue: 27th July 2002
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