Scientists from Exeter and York University are studying the evolution of the menopause, and have found clues to its origin in killer whales.
Humans and orca are two of only three species that evolved to stop having babies half-way through their lives – something even great apes and long-lived elephants do not do. While some have suggested that menopause is a side-effect of our own greater longevity, researchers say that orcas could hold the key to what’s been a long-standing evolutionary mystery.
Killer whales stop having babies in their 30s or 40s, even though they live so much longer. Biologists call it post-reproductive lifespan. We call it menopause. Only three known mammals experience the menopause – orcas, short-finned pilot whales and we humans. Even our closest ape cousins, chimpanzees, do not go through it. Their fertility peters out with age, but female orcas and women evolved to live long, active, post-reproductive lives.
“From an evolutionary perspective, it’s very difficult to explain,” says Prof Darren Croft. “Why would an individual stop having their own offspring so early in life?” Darwinian evolutionary theory says that any characteristic reducing an animal’s chance of passing on its genes to the next generation will be edged out – the process of natural selection. That has led some to argue that menopause in humans is a result of longer life, better health and medical care. But, as well as painting a rather depressing image that post-menopausal women are simply alive beyond their evolutionarily prescribed time, that theory has been largely debunked – thanks, in part, to these orcas. Obviously, medical care is not increasing their lifespan. The question is whether an older female brings a measurable benefit to her existing family which outweighs the genetic cost of having no more babies.
“We noticed that the older females would lead from the front – they’re guiding their groups, their families, around to find food. It’s just like us,” says Croft. “Before we had Google to ask where the shop was, if there was a drought or a famine, we would go to the elders in the community to find out where to find food and water.”
Croft’s findings have turned out to be of great interest to women writing about the menopause. One of them was Christa D’Souza, who published a book earlier this year about her own experience of menopause.
“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 .”We complain, women of my age, of becoming invisible, and it’s true – you realise how very much you’re defined by sexuality. But I have a sense – galvanised by stories about the killer whales – that now is the time when you become the person you really want to be.”
- The Hot Topic: A Life-Changing Look At The Change Of Life, by Christa d’Souza
- Victoria Gill’s documentary The Whale Menopause was first broadcast on BBC Radio 4
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