Scientists have debated for years about why menopause exists. Some have argued that it’s a trait that evolved through natural selection in our ancestors. Women who stopped reproducing ended up with more descendants than women who didn’t. Some scientists proposed that older mothers were better off putting all their effort into caring for their children who were already born, rather than having new ones. As their limited supply of eggs deteriorated, they faced a higher risk of miscarriages and even death during childbirth. (In terms of reproduction, men have it easy by comparison: they can make new sperm through their whole life and don’t have to suffer any of the risks of pregnancy.)
But some studies raise questions about this hypothesis. The risks that childbirth poses to women later in life may not be big enough to make menopause much of an evolutionary benefit. Some scientists have come up with a different explanation: they argue that menopause provides the opportunity for women to help raise their grandchildren. Researchers who studied population records from Finland before the Industrial Revolutionfound that children were more likely to survive till adulthood if their grandmothers were still alive. Menopause might therefore be a winning evolutionary strategy because it leads to more grandchildren who can carry on Grandma’s genes.
But is it even necessary to think of menopause as a special adaptation in humans? Some scientists don’t think so. They argue that what happens to women as they get older is not terribly different from what happens to females of other species. In many species, females are born with a supply of eggs that then gradually deteriorate over their lifetime. They can invest energy into repairing the eggs, but if they invest too much, they have less energy for other tasks. This evolutionary balance leads females to eventually run out of viable eggs. Whether a female survives beyond that point or not simply has to do with how well her body is equipped to resist aging. There’s nothing special, then, about the fact that females in many species, including rats and elephants, can live past their reproductive years.