Most mammals go through the menopause – if they live long enough

Sperm whales are among the few mammal species that are widely considered to undergo menopause

Nature Picture Library/Alamy

Only humans and a few toothed whales undergo the menopause, many sources will tell you. But a paper by Ivana Winkler and Angela Goncalves at the German Cancer Research Center claims that the menopause is, in fact, widespread among mammals. So which is right? The surprising answer is both.

Goncalves studies how the female reproductive tract ages in mice. “It’s absolutely clear that our mice in captivity reach something that is like menopause in humans,” she says. “And yet every time that I present this work to an audience, I get the question, ‘but I thought only humans had a menopause?’”

So Goncalves and Winkler set out to establish which other mammals have a menopause by reviewing published studies.

The first issue is that most other mammals do not menstruate in the sense of bleeding when the lining of the uterus is shed. Instead, the lining of the uterus is reabsorbed.

If you define the menopause in the narrow sense of the ending of menstruation, most mammals cannot undergo it because they do not menstruate to begin with. However, biologists generally use the term in a wider sense.

“The term is used in the literature to mean cessation of reproduction, and does not depend on menstruation,” says Simon Chapman at the University of Turku in Finland.

The key physical thing that results from the menopause is the ovaries stop releasing eggs – the oopause. But finding out if and when most mammals undergo oopause is far from easy.

In some species, the presence or absence of reproductive cycles can be directly established by, for instance, looking at hormone levels in blood. But scientists can usually only do such studies in captive animals. And for most species, researchers have to infer the timing of the oopause from when individuals cease reproducing, which is also typically gleaned from animals in captivity.

In their analysis, Winkler and Goncalves looked at studies that included at least 10 captive individuals. While they found reliable studies for less than 100 species, the results showed that the vast majority of these mammals stopped producing eggs if they lived long enough. In fact, female mammals typically underwent the oopause when they were between one-third and two-thirds of the way through their maximum possible lifespan.

“This shows that the [female] reproductive system stops working much earlier than the rest of the body,” Goncalves says. “And for me, it’s absolutely relevant that this happens in other species as well.”

Previous studies have suggested this is the case, Goncalves says, but theirs is the most comprehensive and rigorous analysis so far.

If the menopause is defined as animals undergoing an oopause when they live to a relatively old age rather than being killed by predators or disease, then Goncalves’s study provides good evidence that the menopause is common in many mammals.

But she is not claiming that most wild females survive long enough to undergo the oopause. “It’s not about what’s happening in the wild,” Goncalves says. And what happens in the wild matters from an evolutionary perspective, she says.

“This paper shows nicely that if you’re kept safe from the dangers of the world, eventually you’ll run out of eggs,” says Sam Ellis at the University of Exeter in the UK.

In 2017, his team showed that, in the wild, females from a few species of toothed whale regularly live for significant periods after they are unable to reproduce. His study is the main source for the claim that the menopause occurs only in humans and a handful of whales. But Ellis agrees it depends on which definition you use.

“I deliberately focused on wild populations, and they’ve deliberately focused on focused on captive populations,” he says. “I think both are equally valid. It depends on the kind of question you’re trying to ask.”

What is clear is that females in the majority of mammal species stop producing eggs long before the end of their maximum potential lifespans, but in the wild few reach this point. Whether this means the menopause is common or rare comes down to how you define it.


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