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Lucy Cooke is a zoologist and author of Bitch: On the Female of the Species.

It’s an odd thing to find kinship with a killer whale. But as I bobbed along in a tiny boat on Washington State’s Salish Sea, I felt a strange communion with the six-tonne swimming torpedo with teeth diving for salmon alongside me. She was around my age, and together we shared a unique biological trait found almost nowhere else in the animal kingdom: We were both on the cusp of menopause.

As a rule, natural selection takes a pretty merciless view of a loss of fertility: If the point of survival is reproduction, there is no benefit in living beyond that point. Famously long-lived females such as Galapagos tortoises, macaws and even African elephants all continue to reproduce well into their twilight years.

For a long time, the only animals known to outlive their fertility were zoo dwellers whose natural lives have been extended by free meals and health care. For example, in the wild, a female gorilla can live up to 40 years, whereas in captivity she could top 60. Her ovaries have an activity shelf-life, however, and, unlike the rest of her organs, they will cease to function in her artificial old age.

Because we naturally outlived our ovaries, women were long considered menopausal freaks. Our anomalous lifespans generated decades of debate and dozens of theories – many deeply dispiriting (and mostly devised by men). One popular explanation states that women, like those zoo-living gorillas, have simply outlasted our ovaries thanks to modern medicine. This implies that menopause isn’t really normal and that women should really bow out gracefully at around 50, alongside our fertility.

Another idea is that menopause is the evolutionary upshot of men’s preference for youthful women. The trio of male scientists from McMaster University that proposed this profoundly depressing theory supported it with some snazzy mathematical modelling demonstrating how the male penchant for young skirt results in the buildup of deleterious mutations, causing older females’ ovaries (if not their hopes and dreams) to shrivel up and die before the rest of them.

Finally there’s the “grandmother hypothesis,” which posits that females who duck out of the reproductive rat race mid-life and focus their energies on supporting their children (and grandchildren) instead of squeezing out more babies, significantly increase their offspring’s chances of survival and, in turn, their own genetic legacy.

This explanation, devised by the American anthropologist Kristen Hawkes, is the most enduring and feminist-friendly, but has always lacked empirical proof. That was until the southern resident orcas (also known as killer whales) splashed in to save us with a lifeline of supporting data.

These natives of the Salish Sea have been studied continuously for more than 40 years and taught us most of what we know about the species, including the orca’s membership to the exclusive menopausal club. Orcas join humans and three other species of toothed whale (namely beluga, narwhal and short-finned pilot whales) as the only known females to have a postreproductive life that’s as long, if not longer, than their reproductive one.

As a woman of a certain age, surfing my own tide of fickle midlife hormones, I simply had to pay them a visit to find out about our strange shared synergy. But studying menopause in an enormous submarine predator is not without its challenges – one of the basic hurdles being how to monitor the hormones that track reproductive senescence. Taking blood samples would be treacherous (for the scientist) and invasive (for the orca).

A less intrusive, if smellier, alternative is to collect fecal samples. This is how I came to be cruising the Salish Sea in search of orca poo on a sunny September afternoon with Deborah Giles, director of research and science at Wild Orca and the southern residents’ official scientific pooper-scooper.

Dr. Giles plies her trade from San Juan Island, one of the hundreds of rugged landmasses left behind by ice age glaciers in the flooded fjord land that straddles Canada and the U.S. Pacific Northwest. Just a short hop on a Kenmore Air seaplane from Seattle, the spectacular 60-minute journey gave me a bird’s-eye view of the crazy cold-water currents and kelp forests that make the Salish Sea such a boon for marine life.

It took just 20 minutes to traverse the tiny island and meet Dr. Giles at Snug Harbor, where her modest boat was docked. She informed me that a shortage of hands meant I was being immediately promoted to spotting and scooping duty. A thousand questions sped through my mind. As a dog owner, I’m no stranger to picking up turds, but it was hard to imagine a bag big enough for this particular job. The ivy-green water looked deep and chilly – not to mention swimming with giant predators. Was diving involved? Ms. Giles handed me a large net and told me not to worry; whales do floaters, big ones.

“Poop is an absolute gold mine,” she said. Scat samples enable her team to monitor not just the orca’s estrogen levels, but also their stress and pregnancy hormones. Researchers can tell what the whales are eating and check for the presence of parasites, bacteria, fungus and even microplastics. So fecal samples provide a health check of the orca’s entire marine ecosystem.

First, Dr. Giles has to find the feces. The words needle and haystack sprung to mind, but fortunately, she has help in the shape of Eba, a former street dog from Sacramento, Calif., who’s been rescued and trained to sniff out whale scat. Eba’s twitching snout contains 300 million olfactory receptors, which, compared with my paltry six million, means she can smell orca poop from a nautical mile away.

Orcas are the most souped-up member of the dolphin family and, like their smaller squeaky cousins, they’re highly social creatures with the smarts to match. Their whopping seven-kilogram brain has more surface area than any other animal on the planet for complex thought processes such as language, social cognition and sensory perception. As if that weren’t enough, their brains have an extra lobe, only found in orcas and dolphins, which suggests they process emotions in a way that we can’t comprehend.

These socially complex brainiacs live in extended family groups or pods of around five to 30 individuals. The southern residents are a clan of three such pods. Originally, it was assumed these pods were led by males, who are significantly larger than females. But it has transpired that the leaders of these hunting clans are not only female, but postmenopausal grannies.

Orcas have highly specialized hunting cultures. Off the coast of New Zealand, they specialize in digging up and devouring stingrays. In Argentina, they surf on to shore to snatch sea lion pups from the beach. Along Alaska’s Unimak Pass, they gather in May to ambush young grey whales.

The southern residents specialize in catching king salmon. But locating these ephemeral salmon hot spots requires a wise and wily hunter, since they change with year, season and even tide. Orcas must decide whether to spend energy following the fish up river or hang out at the salmon deep-sea diner hoping for fresh stock. It’s a complex cognitive job, which has become much harder now that salmon have to navigate an obstacle course of gigantic concrete hydropower dams on their journey to their spawning grounds.

This, combined with warming waters and decades of overfishing, has seen salmon populations crash. When the fish are in short supply, only killer whales with years of experience know how to find them – and those are the oldest matriarchs. These old-lady orcas are essentially the repositories of ecological wisdom that keep their clan alive.

Such female empowerment came as something of a shock to the men studying them. As Ken Balcomb, founder of the Center for Whale Research and one of the original southern resident scientists, told me: “The females were meant to be the harem.”

Male orcas are, it turns out, real mommies’ boys. They spend their entire lives by their mothers’ sides, and the mothers frequently share their hard-caught salmon with them. These hunting handouts literally keep their sons alive.

Decades of data on the southern residents showed that if a male orca’s mother died before her 30th birthday, he was three times more likely to die the next year. But if mom had gone through menopause, his odds of dying the next year went up by 14 times – proving that the older the matriarch, the more valuable her hunting handouts are to her son’s survival.

The same isn’t true of daughters, who also remain part of the clan but were not found to benefit from mom’s hunting handouts. That’s because mothers and daughters are in competition. Whereas sons will sire offspring in other clans, daughters’ offspring will remain in the pod and raising them costs the clan extra salmon – something their daughters will fight hard to get. So it pays for mothers to invest primarily in sons and to stop breeding halfway through life in order to stop competing with their fertile young daughters. All of which supports the grandmother hypothesis.

In recent years, the southern residents have been listed as endangered. A precipitous decline in wild salmon is principally to blame, although pollution – noise and chemical – is compounding their stress. Dr. Giles’s work has revealed high levels of stress hormones and numerous failed pregnancies in the past few years. Worse still, they have lost many of their oldest matriarchs, leaving the group rudderless in a treacherous time.

They are certainly becoming increasingly fragmented. When Dr. Giles and I finally located them, there were just two members foraging in a traditional salmon buffet spot that would once have drawn the whole pod. First I spotted the lofty onyx fin of Lobo, a 19-year-old male, surfacing so close to the boat my heart skipped a beat. Then I clocked his mother, Lea, swimming close by. At 42, she was probably on the edge of her fertility, like me.

For Lea, the death of her ovaries heralded a rebirth of agency – her aged insight commanding her pod’s respect and propelling it forward. She might even become the new leader of the southern residents, I wondered with hope along with an intense sense of awe and inspiration.

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