The Mystery of Elderly Animal Matriarchs - Pacific Standard
Both women and orcas experience menopause. A new study reveals one reason why these matriarchs may prevail, despite their inability to reproduce: wisdom.

Though most female animals have babies up until the end of life, just two species stop reproducing—or exhaust their eggs—long before they die. You might know: One of these menopausal creatures is you.

The other is the killer whale, a mammal that runs out of eggs about halfway through her up to 90-year life. Often explained by the “grandmother hypothesis,” many anthropologists and biologists think humans and orcas experience menopause so that females can stop spending energy on their kids and, instead, save it for the next in line—grandkids.

An elderly female’s insight is so unique and of enough value to her family, she says, that it keeps her alive long after her eggs and reproductive worth expire.

But new research suggests that old women and whales may provide their families with another essential service.

“For the first time, we show that post-reproductive females act as repositories of ecological knowledge,” says social animal biologist Lauren Brent from the University of Exeter, who, along with a team from Exeter, University of York, and the Center for Whale Research, revealed that female orcas employ a lifetime of ecological wisdom to guide their families toward food.

After more than 30 years of orca observations taken off the northern Pacific coast, the finding was recently published in Current Biology. It describes a group’s eldest female as the most common leader of salmon hunts, a crucial role to her family in-tow, as Chinook salmon make up 90 percent of the population’s diet during summer migration.

The elderly females, distinguished by the shape of their fin and the white mark on their back—“as distinct as our finger prints,” Brent says—show especially strong leadership in years when salmon numbers are low and presumably hard to find. Possessing insight of where to forage for scarce salmon is what Brent deems “ecological knowledge,” a unique wisdom of the ocean gained by experience.

Other elderly animals play similar roles, says Susan Alberts, who studies social animal behavior at Duke University. Alberts points to the multi-ton case of the elephant matriarch, a herd’s eldest and most informed female, who can live into her 60s. Matriarchs remember food and water hotspots better than any other member and often lead long-distance travel. They also devise defense schemes to protect their herd from lions.

Still, there’s no definitive proof of menopause for elephants, says Peter Wrege, director of the Elephant Listening Project. Some studies show reproduction slowing around the age of 45, he says, but other females have babies up until the end of life. Our close animal relatives, like the orangutan, don’t seem to experience menopause either, continuing to reproduce very late into their about-50-year lives. (According to some reports, pilot whales, and perhaps other cetaceans, may experience menopause.) So, Alberts poses the question: Why don’t all elderly females require menopause to become an ecological sage?

Perhaps, menopause is not the essential step toward attaining wisdom.

Instead, Brent thinks it could be a token of long life. Environmental prowess “takes age and experience, which younger members of the population don’t have,” she says. Male orcas, which live about half as long as females, probably don’t possess it either, “by simple virtue of the fact that they aren’t as old.” Males die earlier because they tend to face great risks throughout their lives, like competing to mate, Brent says.

An elderly female’s insight is so unique and of enough value to her family, she says, that it keeps her alive long after her eggs and reproductive worth expire. Indeed, some scientists argue that eggs simply have a “short shelf life” compared to the rest of the body, Alberts says.

But Alberts still believes that menopause must play an active and adaptive role: “Eggs don’t expire at the same rate as the rest of the body,” she says. “That’s not normal aging.” If a mammal’s lifespan got longer, then its reproductive years should have extended too, she says, “this still begs an explanation.”

Lead photo: A 98-year-old orca breaches. (Photo: David Ellifrit/Center for Whale Research)

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