The Grandmother Hypothesis

Menopause is one of the great mysteries of biological life. Why is it that human females lose their ability to procreate well before the end of their potential lifespan, yet other primates, and even long-lived species like elephants and fin whales, continue bearing young until the end? Why does menopause universally occur during a short window of time, while other manifestations of aging, such as graying hair, take place gradually and randomly?

Some scientists believe that prehistoric women rarely lived beyond 30 years old, and, since there was no need for females to continue producing eggs much beyond that age, their egg supply was genetically programmed to last about that long. Menopause happens because long-lived modern women simply outlive their egg supply.

Other researchers disagree with this theory. They claim that prehistoric women often survived past menopause, and, as older women, were able to play a crucial role in the survival of the tribe only because they could no longer bear children. In fact, they suggest that it was the grandmothers that gave our human ancestors the freedom to exploit new habitats, and ultimately, populate the entire planet.

Studies of modern hunter-gathering peoples have found that women in their later years, freed from childbearing by menopause, are among the most industrious members of society, gathering food for seven or eight hours a day. These grandmothers help support younger, nursing women who are restricted in their activities because of breast-feeding and childcare. In one study of a hunter-gatherer tribe, researchers found that it was only with the aid of the grandmothers that the older children of nursing mothers received adequate food.

In addition to being free to help out the children of others, menopause confers another advantage. Childbirth can be risky, and, with forced early retirement of their ovaries, post-menopausal women escape that risk. This increases the likelihood that they will be around to assist their own children mature into self-supporting adults.

Finally, women beyond their childbearing years contribute to the survival of the tribe with their accumulated wisdom. Aging members of both sexes serve as repositories of vital survival skills, such as distinguishing poisonous from non-poisonous plants. Since the cessation of childbearing decreases risk for women, it improves their chances of passing on important knowledge to other members of the tribe.  Based on information in: The New York Times, 9-16-97