Why does human menopause even exist? After all, it’s pretty rare in nature. Even female elephants, who can live to a ripe old age of 70 in the wild, continue to be able to reproduce throughout their life spans.
Women are different. So are orca (aka killer) whales, it turns out. Now pioneering animal biology research has uncovered the most likely reason that killer whales stop reproducing in their 30s or 40s yet live for many decades afterward.
The findings shed new light on the role that menopause may play in the lives of humans, too. Hint: It’s about sharing wisdom.
Background: One somewhat downbeat hypothesis holds that when humans first evolved, we didn’t live past reproductive age…but now we do. That makes menopause a kind of accident. Scientists who study killer whales, however, hypothesized that living well beyond reproductive age has benefits. There was already evidence for the “grandmother hypothesis”—the idea that by helping find scarce food supplies, based on their age-earned knowledge, older females help the species survive. But that’s true for animals such as elephants that continue to reproduce. A newer hypothesis holds that menopausal whales compete less with their daughters in having offspring—and that’s good for the entire species, too.
Study: Using an extraordinary database tracking killer whales over 43 years, English researchers analyzed how likely offspring were to survive if both older and younger whales had babies in the same season.
Results: When both younger and older whales bred at the same time, the offspring of the older whales were 70% more likely to die than those of the younger whales. It wasn’t age—the increased mortality didn’t occur for older whale offspring when the younger generation wasn’t simultaneously having babies. It was competition, especially for food supplies. For the sake of the survival of the species, it would be better if older whales didn’t breed—and instead used their food-finding skills to help the entire pod find food supplies during scarcity. Hence, menopause evolved. That benefitted everyone—including their adult sons, who stay with their mothers’ pods and do particularly well when mom showed them where to find salmon. In short, by not having more offspring, grandma killer whales helped the entire species.
Bottom line: Humans aren’t whales, so you can’t draw one-to-one conclusions. But the evidence that menopause has an evolutionary benefit in killer whales adds support to the idea that human menopause isn’t some deficiency or aging problem—but rather a new phase of life in which women can use their hard-earned knowledge to benefit their children…and everyone else. As British writer Christa D’Sousa, author of The Hot Topic: A Life-Changing Look at the Change of Life, put it to the British Broadcasting Service, “The idea of women passing on information; the idea of wisdom with age—there’s a beauty in that that is about something other than being able to reproduce.” For more thoughts on the positive aspects of this new phase of life, see the post by Bottom Line’s “Natural Side of Menopause” blogger Holly Lucille, ND, “Embracing the Menopause Metamorphosis!“
