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The grandmother factor: Why do only humans and whales live long past menopause?

The views expressed are those of the author and are not necessarily those of Scientific American.


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killer whales live past menopause like humans doMost mammals don’t live long past their reproductive years, failing to serve much evolutionary purpose after they can stop passing on their genes to offspring.

Only three long-lived social mammalian species are known break that mold. Killer whales (Orcinus orca), pilot whales (Globicephala macrorhynchus) and humans (as well as possibly some other great apes) all have females that generally live for decades after they cease being able to bear young. So what might we have in common with these cetaceans?

A new study, published online June 30 in Proceedings of The Royal Society B: Biological Sciences, describes a strong link with specific social patterns that might predispose females to live beyond their fertile years.

“Whether it is younger or older individuals that are most likely to refrain from breeding and adopt the role of kin-selected helpers, depends on the pattern of dispersal and mating,” the researchers concluded.

In species in which the males leave home to breed, over a female’s lifetime, she is surrounded by an increasing number of males to which she is not related (as male offspring leave home and others die). Thus, this pattern increases her options for new mates and decreases the incentive for helping to provide for young that are not her own (or carry any of her genes), the researchers, Rufus Johnstone, of the Department of Zoology at the University of Cambridge, and Michael Cant, of the Center for Ecology and Conservation at the University of Exeter, noted in their paper.

For mammals in which the female leaves the group to mate—or in which breeding happens away from the group—a female will find herself surrounded by an increasing number of males to which she is related (as sons, grandsons and other generations of males stick around). In this scenario, it actually behooves her—and the group—to stop mating (and competing for breeding resources that could increase the fertility of younger females) and help younger females raise her progeny. Other research has shown that having a grandmother around to help out confers extra benefits on younger generations.

Although contemporary human societies have given rise to all kinds of moving and mating arrangements, the researchers point out that in traditional human forager societies, “female transfer to the husband’s family at marriage is more common,” and genetic analysis shows an extended human history of “female-biased transfer.” For the two whale species, the researchers noted that both are thought to mate outside of their local groups, leading to “an increase in local relatedness with female age.”

Johnstone and Cant explained that mating patterns are not likely the only factor to contribute to the evolution of menopause and a long post-reproductive life in these three species. But learning more about females’ changing social groups helps to reveal “the underlying similarity between the ape and whale cases… which would otherwise be obscured by the differences in their social structure.”

The jury is still out on whether these marine mammals also endure hot flashes.

Image courtesy of iStockphoto/Lazareva

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  1. 1. JamesDavis 7:38 am 06/30/2010

    It sounds like your grandmother has sit you down and had a woman to woman talk with you. Something else that probably only humans and whales do.

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  2. 2. DuncanB 8:33 am 06/30/2010

    Just thought that I should point out that Killer Whales aren’t actually whales. Although they are Cetaceans, they are actually a species of dolphin, so you might need to modify your title a little :)

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  3. 3. kevinb 9:45 am 06/30/2010

    Elephants.

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  4. 4. americanscientist 10:54 am 06/30/2010

    Elephants aren’t whales either…

    (Sorry, I couldn’t restrain myself)

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  5. 5. goldsoundz 11:18 am 06/30/2010

    Human females live so long after menopause due to advances in medical science (which has effectively doubled their life expectancy), so the link to whales is rather tenuous

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  6. 6. durbrow 2:55 pm 06/30/2010

    Elephants seem to have menopause under natural conditions.

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  7. 7. jerryd 7:40 pm 06/30/2010

    Again not that bright researchers don’t think very well. Facts are women never lived that long until recently as many died young in childbirth, ect from being worn out early. So the chances of them being grandmothers was not very good.

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  8. 8. treehugginconservative 10:59 pm 06/30/2010

    Whales endure as many (if not more) hazards giving birth, surviving disease, and bringing their young to maturity as humans. There is no reason to believe that human women suffer any greater chance of death prior to menopause. And to clarify, yes dolphins are whales. Dolphins are toothed whales (odontocetes) as opposed to baleen whales (mysticetes), which are both sub-orders in the Order Cetacea.

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  9. 9. jim15936 7:37 pm 07/1/2010

    Hey, you forgot about passing on cultural memory and infrequent survival strategies! What do these grandmother-producing species all have in common: Whales, dolphins, elephants, humans, some apes? They are all mobile mammals at the high end of the intelligence scale. Recall that in most primitive human cultures, very "old" men and women (anyone over 40) are revered for their wisdom, that helps the entire tribe survive infrequent perils such as hurricanes, earthquakes, etc. Yes, Grandma often knew best.

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  10. 10. brushcut 11:05 am 07/3/2010

    Having older members of the community in a primitive society has an additional protective function. When escaping a predator attract it is the slower, weaker member who is the most likely to be selected and brought down. The two groups who have the slower and weaker members are the very young and the very old. When an older animal is caught a young one may be spared to live and eventually reproduce. The species is strengthened by the sacrifice of the non-reproductive older member instead of the potentially fecund young one.

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  11. 11. spocka1p 12:06 pm 07/4/2010

    It’s important to point out that, contrary to several posts here, menopause isn’t an artefact of medicine and technology. In hunter gatherers around 50% of women survive to menopausal age (45-50), and life expectancy from that point forward is an additional 21 years.

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