The Evolutionary Mystery of Menopause
Know thyself” is a terrific idea. It’s one of the Delphic maxims—alongside “certainty brings insanity” and “nothing to excess”—that you can find inscribed on the Temple of Apollo. Such knowing could well begin with an evolutionary conundrum: menopause. It’s as if natural selection took “nothing to excess” strangely to heart in the realm of human reproduction. Very few mammals—excepting short-finned pilot whales and possibly Asian elephants—experience anything like a prolonged life stage during which they are alive yet nonbreeding. So long as they draw breath, our fellow mammals release eggs. But not Homo sapiens.
Around age 50, women stop ovulating, a biological mystery because reproduction is the sine qua non of evolutionary success, and yet menopause occurs at an age when women often have a few decades of healthy life ahead of them. Men keep producing sperm (albeit fewer and less viable) into their eighth and even ninth decades. For women, it’s not about becoming unable to make eggs, since every girl is born with all that she will ever have, which await maturation and release. The “how” of menopause is well understood; it is brought on by a dramatic reduction in endocrine hormones, notably estrogen.
Female African elephants breed into their 60s, and blue whales, into their 90s.
But why has selection favored this rapid and consequential decline, causing women’s endocrine machinery to poop out when it does? What are the ultimate, evolutionary reasons? If you like mystery stories, you’re in for a treat. Mark Twain noted that it was easy to stop smoking; he’d done it hundreds of times. It’s easy to explain menopause; there in 2016, and which has been reinforced by two new studies.
