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See Inside November 2010

Why Women Live Longer

Stress alone does not explain the longevity gap

Or at least that’s the idea I proposed in the late 1970s. Since then, the evidence to support this disposable soma theory has grown significantly—something I wrote about in Scientific American in September [“Why Can’t We Live Forever?”]. In my own laboratory some years ago we showed that longer-lived animals have better maintenance and repair systems than short-lived animals do. The longer-lived animals are also the smarter ones, or the bigger ones, or the ones like birds and bats that evolved adaptations such as wings to make their lives safer. If you can avoid the hazards of the environment for a bit longer by flying away from danger or being cleverer or bigger, then the body is correspondingly a bit less disposable, and it pays to spend more energy on repair.

Could it be that women live longer because they are less disposable than men? This notion, in fact, makes excellent biological sense. In humans, as in most animal species, the state of the female body is very important for the success of reproduction. The fetus needs to grow inside the mother’s womb, and the infant needs to suckle at her breast. So if the female animal’s body is too much weakened by damage, there is a real threat to her chances of making healthy offspring. The man’s reproductive role, on the other hand, is less directly dependent on his continued good health.

It is too extreme to say that for all biology cares, males need only to attract a mate and then can pretty much die. A study of children in Tanzania, for example, showed that children who lost a father before the age of 15 tended to be a little shorter than their peers, and height is a reasonably good proxy for health. But children who lost a mother fared even worse—they were shorter, poorer and did not live as long as fatherless orphans. From an evolutionary point of view, however, the drivers of mating success for males are generally not the drivers of longevity. In fact, high levels of testosterone, which boost male fertility, are quite bad for long-term survival.

Women may still struggle to achieve equality in many spheres of life. To be less disposable, however, is a blessing that offers some compensation. There is evidence from studies in rodents that cells in a female body do repair damage better than in the body of a male and that surgical removal of the ovaries eliminates this difference. As many dog and cat owners can attest, neutered male animals often live longer than their intact counterparts. Indeed, the evidence supports the notion that male castration might be the ticket to a longer life.

Might the same be true of humans? Eunuchs were once members of the elite in many societies. In China, boys were castrated to enable them to serve the emperor without the risk of impregnating his concubines. In Europe, such extreme practices were used to retain the singing qualities of boys as they moved into adolescence.

The historical record is not good enough to determine if eunuchs tend to outlive normal healthy men, but some sad records suggest that they do. A number of years ago castration of men in institutions for the mentally disturbed was surprisingly commonplace. In one study of several hundred men at an unnamed institution in Kansas, the castrated men were found to live on average 14 years longer than their uncastrated fellows. Nevertheless, I doubt that many men—myself included—would choose such a drastic remedy to buy a few extra years. 

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