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Designed to Live

Tom Kirkwood took up the evolutionary explanation of aging in part to fight what he says is gerontology�s greatest misconception: that we are programmed to die.

One February night in 1977, Tom Kirkwood, then only 25, was struck by the biggest insight of his life—“my �Eureka!� moment,” he calls it. Like Archimedes, it hit him while he was in the bath.

Copyright © 2003 Acumen Sciences, LLC All Rights ReservedDr. Kirkwood—who holds a doctorate in biology and is head of gerontology at the University of Newcastle upon Tyne—had grasped the implications of a forced trade-off between the two most important things in life: sex and death. He had come upon it after contemplating the way aging might manifest itself in the two basic kinds of cells—those of the body (or soma, in Greek) and those of reproduction (the germline). Energy lavished on one, he realized, must come at the expense of the other, yet only the reproductive cells need to resist the ravages of age. Genetically, the body is as disposable as a snake�s skin.

For how long, then, will you need your body? Only so long as you might reasonably expect to survive the slings and arrows—and fangs, famines, and acute illnesses—that decimated our ancestors in the Stone Age, when our genetic heritage was forged. Very few of those ancestors lived past 60; most died much earlier.

This scientific theory contrasts sharply with the competing popular notion of programmed death, which holds that the body self-destructs in the service of some higher good, like fending off cancer or clearing the field for the next generation. It also allows scientists to make certain predictions, some of which Dr. Kirkwood and his collaborators have confirmed.

They studied the life histories of tens of thousands of British aristocrats and found that those who lived the longest tended to have the smallest families. They bred fruit flies for longevity over a period of many generations and found that the resulting Methuselah flies were less prolific than their wild cousins. They also cite the better-known case of eunuchs, who outlive other men, and of geldings (like Funny Cide, this season�s equine star), which may race long past the age at which stallions are often put out to pasture.

Perhaps the most critical implication of the theory, that aging mechanisms must involve the self-maintenance of somatic cells, has been vindicated by several experiments. In one, skin cells taken from long-lived species did much better under oxidative stress from bleach and other chemicals, than did those from shorter-lived species.

The theory also makes predictions regarding the age-related damage that accumulates even in germ cells—spermatozoa and ova. Such damage explains why older mothers are more likely to have children with genetic defects; but extra resources, for self repair, and quality-assurance processes to screen out bad ova and spermatozoa, ensure that genetically normal babies start life utterly new.

“The disposable soma obviously makes sense,” says George Williams, Ph.D., professor emeritus at the State University of New York at Stony Brook and the doyen of aging evolution. “Fecundity has a cost.”