Whales That Go Through Menopause Live Longer and May Help Care for Grandchildren

Like humans, a handful of toothed whales go through menopause—and new research suggests the trait could have evolved for similar reasons across species.

Female whales that go through menopause have longer lifespans than those that don’t, surviving decades past their reproductive prime, according to the study published Wednesday in the journal Nature. They might produce fewer offspring as a result, but these older females have more time to help raise younger generations, without having to compete with their daughters to reproduce.

“They’ve done a great job of compiling all the evidence,” Michael Gurven, a behavioral ecologist at the University of California, Santa Barbara, who did not contribute to the findings, tells USA Today’s Elizabeth Weise. “This paper quite elegantly gets at these very difficult issues.”

“This is a piece of work that very much needed to be done,” Megan Arnot, an evolutionary anthropologist at University College London who was not involved in the research, says to Live Science’s Gennaro Tomma.

Menopause is rare among animals—females of only six mammal species are known to go through it. Humans are one, and the remaining five are toothed whales. (Though a study published last fall suggested some chimpanzees experience menopause, too.)

“When you think about it from a natural selection point of view, it’s a very unusual thing to do,” Samuel Ellis, who researches social behavior at the University of Exeter in England and is the first author of the new study, tells the Washington Post’s Maggie Penman and Dino Grandoni. “If the aim is to get as many offspring into the next generation as possible, almost always the best thing is to reproduce for your whole life, which is what most mammals do.”

One theory for why menopause evolved is the grandmother hypothesis: that by continuing to live after they stop reproducing, female mammals can care for their grandchildren, increasing the likelihood that the younger generations pass on their grandmother’s genes. Previous research has found that for humans, the presence of maternal grandmothers tends to increase the survival rate of their grandchildren.

A paper in @Nature suggests that menopause in toothed whales may have evolved to increase total lifespan. The findings suggest the evolution enables females to help younger generations survive, without competing with daughters or granddaughters for mates. https://t.co/KvLYeEkN2c pic.twitter.com/NwlJ43MuoV

— Nature Portfolio (@NaturePortfolio) March 13, 2024

For the new study, researchers looked at menopause in whales, where it has evolved multiple times. They put together a database of toothed whale life histories and estimated lifespans of females across 32 species, including the five that undergo menopause: narwhals, killer whales, false killer whales, short-finned pilot whales and beluga whales.

The team calculated toothed whale lifespans by looking at the ages of whales that had died, and they estimated reproductive lifespan from indicators of ovarian activity in dead whales.

They found that in species with menopause, females live around 40 years longer than same-sized species without it, despite having similar reproductive lifespans. The findings suggest that older females play a role in helping their descendants survive during a time when they’re not competing to reproduce.

“Evolution has selected for a longer female lifespan so that mothers and grandmothers can continue to provide support to their family well after reproduction,” Ellis says of the whales to Reuters’ Will Dunham. “We see just the same patterns in human societies where women have a similar reproductive period to our closest primate relatives but have a much longer total lifespan.”

Scientists have also gathered observational evidence of older female whales helping others. For example, they’ve seen grandmother killer whales taking care of young orcas and leading less experienced generations to where they can find more fish, per the Washington Post.

Grandmother killer whales also catch salmon and break it in half to share, Darren Croft, a co-author of the study and behavioral ecologist at the University of Exeter, tells USA Today. He worked on a study of killer whales last year that found males with older mothers have fewer scars, suggesting moms protect their sons after they’ve stopped reproducing.

Rebecca Sear, a demographer at the London School of Hygiene and Tropical Medicine who did not contribute to the findings, notes in a commentary accompanying the new study that the researchers were looking primarily at stranded whales to gather their data on lifespan and reproductive lifespan, which may not be representative of all whales.

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Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.