A Blog by Ed Yong

Why Killer Whales Go Through Menopause But Elephants Don’t

Last summer, I met Granny. I was on a whale-watching boat that had sailed south from Vancouver Island, in search of a famous and well-studied group of killer whales (orcas). Two hours after we set off, we started seeing black fins scything through the unusually calm and glassy water. We saw a dozen individuals in all, and our guide identified them by the shape of their fins and the white saddle patches on their backs. Granny, for example, has a distinctive half-moon notch in her dorsal fin.

Seeing her, I felt an intense and solemn respect. She is the oldest member of the group, perhaps the oldest orca on the planet. Her true age is unknown, but a commonly quoted estimate puts her at 103, which would make her a year older than the Titanic, and far more durable. Imagine all that she has seen in that time: the generations of her children and grandchildren; the countless pursuits of fleeing salmon; the increasingly noisy presence of fishermen, scientists and gawking tourists. Decades of knowledge and wisdom live in her brain. Ad that knowledge might explain one of the most unusual features of killer whale biology—their menopause.

Animals almost always continue to reproduce until they die. There are just three exceptions that we know of: humans, short-finned pilot whales, and killer whales. In all three species, females lose the ability to have children, but continue living for decades after. That’s menopause. Female killer whales go through in their 30s or 40s. Why? Why sacrifice so many future chances to pass on your genes to the next generation?

One of the most compelling explanations is called the grandmother hypothesis. Proposed in 1966, it suggests that older females forgo the option to bear more children so they can support their existing ones. By helping their children and grandchildren to survive and thrive, they still ensure that their genes cascade down the generations.

In 2012, Darren Croft at the University of Exeter found evidence to support this hypothesis. His collaborator Ken Balcomb had been studying the resident killer whales of the Pacific Northwest since the 1970s; his astonishingly thorough census had captured the lives, deaths, and family ties of hundreds of these whales.

By ploughing through the data, student Emma Foster showed that if a male orca’s mother died before his thirtieth birthday, he was three times more likely to die the next year. If she passed away after he turned thirty, he was eight times more likely to subsequently snuff it. And if mum had gone through menopause, his odds of dying went up by fourteen times. The data were clear: mothers help their sons well into adulthood, and older mums are especially helpful.

“But that left a big unanswered question,” says Croft. “Old females are keeping their offspring alive, but how? What is it that they’re doing to confer the survival benefit?”

One reasonable guess involves salmon. Salmon makes up 97 percent of the diet of these particular orcas, and salmon are unpredictable. “They’re not distributed equally in space,” says Croft. “There are hotspots that differ with season, year, tide.” So just like human fishermen, the orcas need to know when and where to go to catch their fish. Do they stay at sea or swim inland? Do they go up their inlet or that one? The oldest females might be better at making these decisions, thanks to their accumulated experience.

To test this idea, the team turned to video footage of the southern residents, which Balcomb’s team had captured between 2001 to 2009. Postdoc Lauren Brent analysed over 750 hours of video to work out which whales were swimming together, and who was following whom. She also collected data from nearby fisheries to work out how big the salmon stocks were at different times.

She found that adult females are more likely to lead a group than adult males, and older post-menopasual females (who make up a fifth of the pod) were more likely to lead than younger ones. This bias was especially obvious in seasons when salmon stocks were low. And, as Foster found, there was a sex bias—males were more likely to follow their mother than females were.

These simple trends support the idea that the post-menopausal orcas are “repositories of ecological knowledge”. They lead the others to food, and their skills are especially important at times when food is scarce. And in doing so, they help their young to survive, which offsets the costs of forgoing any further reproduction. “That doesn’t tell us why they stop reproducing,” says Croft. “You could share information while still being reproductive. Why did they stop? That’s the next question.”

The same principles apply to human menopause, too. Some scientists have suggested that human menopause is merely a side effect of our longer lifespans, brought about by medicine and sanitation. But that can’t be right. Among many hunter-gatherers, like the Ache of Paraguay or the Hadza of Tanzania, around half of women survive to 45, and continue living into their late 60s. Like killer whales, they live long after the stop reproducing. And like killer whales, the longer they live, the more they know. In 2001, anthropologist Jared Diamond wrote:

“Old people are the repositories of knowledge in preliterate societies. In my field studies of New Guinea birds, I start work in a new area by gathering the oldest hunters and quizzing them… When the hunters are stumped by my asking about some especially rare bird, they answer: “We don’t know, let’s ask the old man (or woman).” We go into another hut, where we find a blind and toothless old person who can describe a rare bird last seen 50 years ago. Some of that stored information is essential to the survival of the whole village, whose members include most living relatives of the old person. The information encompasses wisdom about how to survive dangers — such as droughts, crop failures, cyclones and raids — that occur at long intervals but that could kill the whole tribe if it did not know how to react.”

Why, then, don’t elephants go through menopause? They are also long-lived animals that stay in family groups, and the old females—the matriarchs—are vital. They are better at recognising friendly faces and they know the best anti-lion moves. They provide their herds with the same benefits that orcas like Granny bestow upon their pods.

But resident killer whales differ from elephants in one critical respect: their sons and daughters stay in the groups where they were born. This means that as a female grows older, her pod becomes increasingly full of her own children and grandchildren. Over time, she becomes increasingly related to her neighbours, and she shares more and more of her genes with her neighbours. This creates a powerful impetus to shift her efforts away from having more children, and towards helping her existing descendants.

That impetus doesn’t exist in elephants because their sons eventually leave their birth group to find new ones. Females become less related to their group-mates over time or, at least, no more related. A matriarch’s best bet, then, is to carry on reproducing until she dies.

And humans? Many anthropologists believed that we started off with female-biased dispersal—that is, daughters would leave to join new groups. “When she joins, she has zero relatedness to the rest of the group,” explains Croft. “But as she ages, she has offspring and her local relatedness increases.” Then again, other animals like hamadryas baboons and the Seychelles warbler also have female-biased dispersal and don’t go through menopause. “So, it’s not just about the dispersal patterns but also the role that old females can play in the group,” says Croft.

In killer whales, the old females might also be better at catching salmon, which they then share with their kin. Perhaps they understand the hierarchies and structures of other groups, and mediate fights between their sons and rivals. These ideas are harder to test. “We have so little information on them,” says Croft. “We see them at the surface and we know so little about their lives.”

Reference: Brent, Franks, Foster, Balcomb, Cant & Croft. 2015. Ecological Knowledge, Leadership, and the Evolution of Menopause in Killer Whales. Current Biology http://dx.doi.org/10.1016/j.cub.2015.01.037

More on menopause:

Why do killer whales go through menopause?

Did conflict between old and young women drive origin of menopause?

The heavy cost of having children

20 thoughts on “Why Killer Whales Go Through Menopause But Elephants Don’t

  1. The value of keeping older members of the community alive would go up radically for a species which had developed syntax. Someone should look into orca communication with that in mind, if it’s not being done already.

  2. I don’t think the grandmother hypothesis was proposed in 1966. Williams had similar idea but he didn’t coin the term.

  3. Actually, there’s a number of studies showing elephants go through menopause (along with many other mammals). Too many to cite, but see here:

    Mackey et al. 2006 South African Journal of Wildlife Research Vol. 36, No. 1, April 2006

  4. Doesn’t this paragraph imply the opposite of what is stated? It has lots of data about chances of death _increasing_ without an older orca around

    By ploughing through the data, student Emma Foster showed that if a male orca’s mother died before his thirtieth birthday, he was three times more likely to die the next year. If she passed away after he turned thirty, he was eight times more likely to subsequently snuff it. And if mum had gone through menopause, his odds of dying went up by fourteen times. The data were clear: mothers help their sons well into adulthood, and older mums are especially helpful.

    1. I agree. This paragraph clearly states that the longer the mother lives, the greater the likelihood of the male offspring dying. It must be a mistake, and the odds given are of the offspring surviving the longer the mother lives.

  5. This article does a great job outlining, with updated research, what those of us in the NW orca community have “known” for a long time. However, I would LOVE to see a picture of a female orca on an article about matriarchal structures – perhaps one of Granny, J2, the main orca in question? What you’ve got there is a mature male. 😉

  6. Check out the respect given to elders’ wisdom in ancient cultures …the Chinese, Indian and aboriginals.

  7. Jared Dimond is certainly not an anthropologist. His quote about the “toothless old man” is also offensive –he wouldn’t describe academic experts that way, would he? I like the underlying insights of the article for orcas and elephants but when it veers towards human social behavior it stretches beyond what most ecologists and physical anthropologists have expertise in.

  8. It looks like my earlier attempt to comment disappeared in moderation. I don’t know if you didn’t like it, or what. So let me try again.

    You wrote: “And if mum had gone through menopause, his odds of dying went up by fourteen times.” On its face, that sentence argues against menopause. It says that going through menopause causes your progeny to die at a horrible rate. You would think that would be selected against. To a large extent.

    So, what were you really trying to say? Did that sentence really mean to say something like, “And if mum died after going through menopause . . .”?

    But even that seems a bit strange (though more plausible), since the female had to die eventually. Anyways, I’m just finding that progression of statements unclear and I’m not sure just what you are trying to say with it. Is it that after an extended period of menopause, when the mother finally dies, that is what tremendously increases the death rate of her offspring?

  9. Really interesting! Where could I find further information on “anthropologists believed that we started off with female-biased dispersal” for humans? I’m interested because male based dispersal makes more logical sense for support during pregnancy and child birth so I would love to read more about this. Thanks!

  10. ” And if mum had gone through menopause, his odds of dying went up by fourteen times.”
    I feel very stupid, but how is this a good thing? Or does it mean that if she had gone through menopause *and died* …?

  11. Both humans and whales are at the top of a long food chain. We know that because of the accumulation of toxins the risks go up the later in life a woman has a child. This is true for orcas as well, so their cultural preference for early reproduction is probably a good survival instinct.

  12. Some interesting ideas here. But like other commenters, I’m left confused by the paragraph in which you state,

    “By ploughing through the data, student Emma Foster showed that if a male orca’s mother died before his thirtieth birthday, he was three times more likely to die the next year. If she passed away after he turned thirty, he was eight times more likely to subsequently snuff it. And if mum had gone through menopause, his odds of dying went up by fourteen times. The data were clear: mothers help their sons well into adulthood, and older mums are especially helpful.”

    But it sounds like you’ve made exactly the opposite case to your conclusion; that is, the longer mom lives, the more likely her son is to die.

    Also, like another commenter here, I was struck by the statement “Many anthropologists believed that we started off with female-biased dispersal—that is, daughters would leave to join new groups.” Don’t most anthropologists, in fact, believe that we “started off” with males dispersing and female relatives remaining cohesive (matrilineal/matrifocal) until the advent of agriculture? But then it’s not clear why this matter is even mentioned since, as you point out, matrilineal dispersal patterns in other animals don’t correlate with menopause, so this matter of dispersal doesn’t add much weight or really go anywhere.

  13. Killer whales and humans have one big thing in common – no predators. It makes sense to invest heavily in the survival of your offspring when predation is not an issue, but when it is, it becomes more beneficial to invest in numbers. The difference becomes clear when comparing short-finned pilot whales, which have post-reproductive females, to long-finned pilot whales, which do not. The long-finned pilot whales have higher predation mortality and overall a slightly lower life expectancy. This could also explain the difference between killer whales and elephants.

    1. Someone above said that elephants do go through menopause. Given their famed long memories and more recently discovered culture and social organization, I would certainly look for it.

      In regard to ‘male menopause’, males do not pay the physical costs of pregnancy, so fertility shouldn’t shorten their lives. However, at least in humans, most of them experience a significant decline in the production of testosterone, which would decrease their tendencies to fight and engage in other risky behaviors, thus, if they survived their youth, they might live longer to impart their memories to the community.

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