Grandmothers: Their childcare was crucial to evolution, says new study

Grandmothers were crucial to human evolution – increasing life spans by offering childcare, a new study shows. We moms don't need a PhD to know that – do we?

Ann Hermes / The Christian Science Monitor
Grandmothers were crucial to human evolution by increasing life spans through childcare, a new study shows. Here, Rita Cheong arrives to babysit her great-grandchild, Annika Liu, as the child's mother, Ingrid Ahlgren, leaves the apartment for work in New York, May 1, 2012.

My mother is going to like this one.

Grandmothers, it turns out, are super duper important – not just in their own families, but for the human species overall.

A new study published today in the British biological journal “Proceedings of the Royal Society B”  gives new mathematical support for a long standing theory called the “grandmother hypothesis” – basically the idea that humans developed longer lifespans than apes because grandmas (or nanas, grammies, gogos, bubbas; take your pick) helped feed their grandchildren.

Test yourself: Are you a helicopter parent?

The theory goes basically like this:

Since grandma was keeping an eye out for the nutrition of Baby 1, mom could concentrate on making Baby 2. On average, then, women with able-bodied mothers had more kids, which meant that long-living grandmothers passed along their longevity genes to more descendants.

Voilà! Longer-living humans. (OK, a little more complicated than that, but you get the idea.)
This is important to remember when your mom inquires as to whether your baby is eating enough. She’s got the species in mind. Really.

Professors from the University of Utah and the University of California, Los Angeles first proposed the grandmother hypothesis in 1997, after they had lived with hunter-gatherer people in Tanzania and noticed that older women spent their days gathering food for their grandchildren. This was different than other mammals, they realized. They incorporated additional research, and came up with their theory.

But there has been a lot of debate about the grandmother hypothesis, in large part because it lacked a mathematical foundation.

And that’s just what the new study attempted to add.

Kristen Hawkes, a University of Utah professor and one of the scholars who first proposed the grandmother hypothesis, was the senior author on the study. She and her fellow researchers developed computer simulations through which they could test the impact of a little bit of grandmothering on life expectancy. It turns out, they found, that within 24,000 to 60,000 years of grandmothers caring for grandchildren, simulated creatures lived 49 years after reaching adulthood – almost two and a half decades longer than without grandma. This just about correlates with the life expectancy of humans versus apes.

(And yes, we realize 24,000 to 60,000 years might be a bit longer than your family has to shift child care arrangements. But in evolutionary terms it’s pretty minor.)

Ms. Hawkes says that she believes grandmothering was the first step that led to other factors that also influenced life span, such as the development of larger brains.

A competing “hunting hypothesis” says that as natural resources diminished, there was natural selection for humans with larger brains, who could be savvier about hunting methods. Those larger brains then led to longer lifespans.

But Hawkes theorizes that larger brains actually stemmed from grandmother involvement with children. (See, I told you my mom would love this.)  Because women could have more children closer together, there was more impetus for babies to actively engage their caregivers.

“If you are a chimpanzee, gorilla or orangutan baby, your mom is thinking about nothing but you,” Hawkes told her university’s news center. “But if you are a human baby, your mom has other kids she is worrying about, and that means now there is selection on you – which was not on any other apes – to much more actively engage her: ‘Mom! Pay attention to me!’ ”

RELATED: Are you a helicopter parent? Take our quiz!And hence the bigger brains.

“Grandmothering was the initial step toward making us who we are,”  Hawkes said.

And, when you’re lucky, they can be really helpful with babysitting.

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