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How Human Society Was Built By Grandmas

Next time you get the impression you’re not getting respect as the grandma, remind that person human society might not even be here if it weren’t for us grandmas. Please read on…

University of Utah anthropologist Kristen Hawkes. (Lee J. Siegel/University of Utah)

Grandmothers: They feed you, they spoil you, they constantly needle you about your relationship status.

And, according to anthropologist Kristen Hawkes, they might be the driving force behind the evolution of much of human society.

Hawkes, an expert in human evolution and sociobiology at the University of Utah, is the author of several studies on the “grandmother hypothesis,” which asserts that many of the characteristics that distinguish us from our ape ancestors are thanks to the thoughtful care of our mothers’ mothers. In the latest, published Tuesday in the Proceedings of the National Academy of Sciences, she and her co-authors explain how grandmothering is a crucial factor behind the spread of monogamy.

The ancient evolutionary explanation goes like this: When grandmothers started to help out with child rearing, they freed up mothers to have more children, more quickly. Those longer-lived grandmothers end up having more grandchildren, each of whom carried their genes for longevity, helping to increase the human life span. Longer lives and larger kin networks also made it more advantageous for men to mate with and protect a single women, so humans relationships became monogamous.

No wonder grandma is always asking why you aren’t married yet.

The chain of events that connects the existence of grandmothers to monogamous relationships is convoluted but compelling. It starts, Hawkes explains, with the Hadza people of northern Tanzania.

Hawkes began studying the Hadza in the 1980s. They are among the last hunter-gatherers in the world, and their way of life has persisted unchanged for tens of thousands of years. The fact that they eschew agriculture and continue to hunt and forage as their ancestors did makes their community a rare window onto human’s prehistoric past, Hawkes explained.

One of many things she and her colleagues noticed was that the older Hadza women were “these amazingly productive tuber diggers,” she said. “They gathered this really important food resource that little kids are just too little to be good at finding,” and then fed the tubers to the children.

A Hazda couple and child in northern Tanzania in 1985. (James F. O’Connell/University of Utah)

The sight of grandmothers feeding children might seem mundane to those of us whose own grandmas insist on plying us with food whenever we visit. But for Hawkes, it sparked a “eureka” moment.

The presence of post-reproductive women is something of an anomaly in the natural world, where, as anyone who has watched a nature documentary can attest, the prime directive is to find food and a mate. Among primates, humans are the only species that continue to live beyond menopause. Since having children is what drives evolution, there’s no good evolutionary reason for women to live past their ability to reproduce — at least as far as nature is concerned.

In a 1997 study in the journal Current Anthropology, she and fellow anthropologists James O’Connell and Nicholas Blurton Jones argued that long post-monopausal lifespans evolved as older women began to play a greater role in caring for young. If a grandmother was around to help out with her daughter’s children, the daughter was able to have more babies more quickly, rather than waiting until their older children were capable of caring for themselves (humans are also the only primates who give birth to a second child before the first is fully mature).

The longer a woman lived, the more grandchildren she was able to care for, meaning that the longest-lived grandmas had the most descendants and were best able to pass along their longevity genes. Over the course of millennia, this resulted in human lifespans that lasted decades past the point at which women were able to have children.

So, next time, you get a little razzing about being a grandma…tell em to put that in their pipe and smoke it….

Sarah Kaplan

About the author

Climate and science reporter
Education: Georgetown University, B.S. in International Culture and Politics

Sarah Kaplan is a climate reporter covering humanity's response to a warming world. She previously reported on Earth science and the universe.

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