After all, what’s the point? Once you’ve passed your genes on to the next generation, why stick around? Why take up space and use food and other scarce resources? It’s the young who need those things to live to reproductive age. So why do old animals even exist? Or old people?
Evolution has no reason to favor long life, Steven Austad, a former lion tamer and now a bio-gerontologist at the University of Alabama at Birmingham, points out. Quite the contrary, he says: “Evolution favors early, copious reproduction at the expense of later life survival.”[i]
S. Jay Olshansky, a biodemographer at the University of Illinois, Chicago, puts it this way: “We age because Mother Nature turns her back on us once we’re in the post-reproductive region of the lifespan. Natural selection didn’t build in a program to make us fall apart later in life.”[ii]
And yet here we are, a world with growing numbers of old people, even very, very old people. Was it “supposed” to be this way? Come to think of it, why is there even such a thing as menopause? Why do women live 30, 40, 50 years past reproduction? (There’s less of a question about old men – some can produce viable sperm until the day they die, though getting it to its proper destination can get iffy).
Perhaps, as one school of thought suggests, aging exists because old animals – especially females – provide evolutionary advantages, not to the old animal herself, but to her offspring and genetic relatives. It’s the so-called “grandmother effect.”[iii]
“If you are a human female and you are taking care of your grandchild… your act of taking care of your grandchild is a reproductive act,” at least in the eyes of evolutionary biologists, says Michael Rose, a professor of ecology and evolutionary biology at the University of California, Irvine.[iv]
Actually, grandfathers are sometimes just as important as grandmothers because they, too, share food, and sharing is evolutionarily crucial, says Harvard University evolutionary biologist Daniel Lieberman.[v]
A hunter-gatherer mother requires enough calories to sustain not just her own body but the bodies of her children as well, Lieberman notes, which means that hunter-gatherer females who are lactating and caring for young children struggle to get enough energy.
“But grandmothers and grandfathers are unencumbered – they can produce a surplus,” he says. “And that energy goes toward the family. As soon as humans started sharing, there was a strong selective pressure for longevity.” (Longevity, as we’ll soon see, is also fostered by “nice” environments, with lots of food around.[vi])
Among other things, older animals are handy because they know where to find long-forgotten watering holes or food supplies. Female post-menopausal killer whales (orcas) are terrific resources for their tribe – they know where scarce salmon are and are often the ones who lead others to food when supplies are low.[vii]
Old female elephants are great resources, too.[viii] In fact, elephant societies are famously matriarchal, with older females helping their herds survive droughts, food scarcity, poachers and, of course, lions.[ix] [x]
Some traditional human societies with long-lived men and women show a similar pattern, says Jared Diamond, a professor of geography at the University of California, Los Angeles who for more than 50 years has studied New Guinea farming societies.
To be sure, he says, nomadic, hunter-gatherer societies aren’t always kind to old people, who may be cast out to die or simply left behind if they can’t keep up with the group’s wandering.
But in sedentary traditional societies, old folks are valuable. “In traditional societies without writing, older people are the repositories of information,” Diamond says. “It’s their knowledge that spells the difference between survival and death for their whole society in a time of crisis caused by rare events for which only the oldest people alive have had experience.”[xi]
That’s exactly what happened in 1993, when an outbreak of the hanta virus triggered a spate of deaths on the Navajo reservation in the Four Corners area of the American Southwest. The virus, originally, and unfairly, dubbed the “Navajo flu” and since renamed the Sin Nombre (No Name) virus, is carried by deer mice. When the feces of deer mice dry up and become aerosolized, humans can unknowingly breathe the contaminated dust and come down with often-fatal pulmonary infections.
When the outbreak hit, scientists from New Mexico’s health department and the federal Centers for Disease Control and Prevention flocked to the Navajo reservation to study the virus. But it was their wise decision to talk with Navajo elders that cracked the case.[xii] [xiii] [xiv]
The Navaho elders remembered that twice before in the 20th century, they had observed a connection between increases in rainfall, a booster crop of pinyon nuts, and a surge in the deer mouse population. In 1993, those exact conditions pertained – unusually heavy rains, lots of snowmelt, huge quantities of pinon nuts, a surge in deer mice, and a not-new-after-all epidemic deciphered by the oldest folks around.
Clearly, then, there are some benefits for the group as a whole to have to older animals or people around.
But this can’t be the whole story. After all, evolution didn’t “plan” for older people to hang around because evolution doesn’t “plan” anything. There must be some other reasons, including genetics, why some creatures live long past reproductive age.
Indeed there are. I explore many of these in my new book, Exercise is Medicine. I hope you’ll be as fascinated as I was.
[i] Austad, S. (personal communication, Feb. 23, 2016).
[ii] Olshansky, S.J. (personal communication, Aug. 15, 2016).
[iii] Abrams, L. (2012, Oct. 24). The Evolutionary Importance of Grandmothers. The Atlantic. Retrieved from https://www.theatlantic.com/health/archive/2012/10/the-evolutionary-importance-of-grandmothers/264039/
[iv] Rose, M. (personal communication, Aug. 15, 2016).
[v] Lieberman, D. (personal communication, Aug. 12, 2016).
[vi] Kaeberlein, M. (personal communication, Oct. 8, 2016).
[vii] Yong, E. (2015, Mar. 5). Why Killer Whales Go Through Menopause But Elephants Don’t. Phenomena, National Geographic. Retrieved from http://phenomena.nationalgeographic.com/2015/03/05/why-killer-whales-go-through-menopause-but-elephants-dont/
[viii] Yong, E. (2015, Mar. 5). Why Killer Whales Go Through Menopause But Elephants Don’t. Phenomena, National Geographic. Retrieved from http://phenomena.nationalgeographic.com/2015/03/05/why-killer-whales-go-through-menopause-but-elephants-dont/
[ix] Fishlock, V. (2011, Jun. 9). Why Matriarchs Matter in Elephant Society. International Fund for Animal Welfare. Retrieved from http://www.ifaw.org/united-states/node/2842
[x] Ogden, L.E. (2015, Jan. 26). The Power of Elephant Matriarchs. National Wildlife Federation. Retrieved from https://www.nwf.org/News-and-Magazines/National-Wildlife/Animals/Archives/2015/Elephant-Family-Behavior.aspx
[xi] Diamond, J. (2013, Nov.). How Societies Can Grow Old Better [Lecture transcript]. TED. Retrieved from https://www.ted.com/talks/jared_diamond_how_societies_can_grow_old_better/transcript?language=en
[xii] Wrobel, S. (1995). Serendipity, science, and a new hantavirus. FASEB Journal: Official Publication of the Federation of American Societies for Experimental Biology, 9(13). 1247–1254.
[xiii] Foreman, J. (1993, Jun. 14), Stalking a Mystery Illness. The Boston Globe. Retrieved from https://www.highbeam.com/doc/1P2-8232177.html
[xiv] Foreman, J. (1993, Jun. 7). CDC Seeks Further Tests at Reservation for clues to disease. The Boston Globe. Retrieved from https://www.highbeam.com/doc/1P2-8231069.html