Why We Should Be Thanking Grandmas For Human Evolution

Why We Should Be Thanking Grandmas For Human Evolution

June 3, 2019 Updated June 5, 2019

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From a parent’s perspective, it seems fair to say that most grandmas are the over-indulgers in our children’s lives. They spoil them rotten, love them endlessly, and pick up the slack for Mom and Dad when it’s desperately needed  —  it’s just what grandmas do.

Some might attribute this behavior to their many years of experience in “motherly love” and nothing more. But could it be more than just sentimental? Could these tendencies stem from evolution and not just a strong background in parenthood?

Well, science shows that it just might be more evolutionary that we had thought.

We often assume that thousands of years ago, in the day of early humans, that the man of the family was the one who provided food for the rest of the family through hunting. Maybe it’s due to childhood stories, Hollywood movies, or history book pictures — but whatever it may be, you’ve likely thought hunted meat from the hands of men is what kept our ancestors thriving.

But did it really go like this? Can we really credit dads as the ones who kept the blood-line running? Or, was someone else responsible for food falling into children’s tummies?

New research now shows that the early humans’ means for survival might not look how we’ve always imagined, and men might not have played as prominent a role in the survival of their families as we once thought.

The true generation-sustainer? Grandma.

Kristen Hawkes is an anthropologist at the University of Utah who studies modern-hunter gatherers like the Hadza, who likely lived in the area that is now northern Tanzania for thousands of years. Because the Hadza way of living today offers the closest look into the way African ancestors lived thousands of years ago, their villages have been the subject of hundreds of scholarly articles and research for over 60 years.

Over a series of extended field visits, Hawkes and her colleagues were able to track how much food a wide sample of Hadza people were able to bring home. And when logging and tracking the success rates of the Hadza men in the community, Hawkes tells NPR, “They almost always failed to get a big animal.” 

More specifically, Hawkes and her team were only able to find success in 3.4% of those expeditions. Which means, if families were solely dependent on the man of the household as a means for survival, they would have starved.

Hawkes’ team came to the conclusion that, at least in this part of the world, the young and elderly women were the main source of finding and harvesting nutrition (mostly digging for tubers) for families — not the men. 

But another surprising factor took hold: Once the mother birthed her second child, it seemed her relationship with her first-born diminished, and in came Grandma to save the day. Meaning, from the evidence in this community at least, grandmothers played a vital role in human evolution.

According to a publication written by Hawkes, the grandmothers’ foraging hours are the exact inverse of those of the nursing mother. Whereas the nursing mother stops or slows foraging in the days immediately following birth, Grandma is usually kicking it up a notch. As the nursing mom continues to progress through the breastfeeding stage, her foraging hours start and continue to increase in order to accommodate the weaned child(ren). As the youngest child grows closer to weaning age, Grandma reduces her hours of food gathering work. If not for Grandma stepping in to save the day in these instances, the weaned children of the household would’ve consequently suffered.

So, really, it’s no wonder grandmas are always trying to overfeed our kids nowadays. In a sense, it’s what biology has trained them to do. But it would seem stuffing grandchildren with food isn’t the only thing that our ancestral grandmas did to keep the evolutionary train rolling.

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When humans are forced to live off the land, it’s likely they survive in an environment where it’s vital to defend their families or homes from hostile enemies. Though disturbance of sleep in the form of early rising may act as an annoyance to the elderly with tired eyes, sleeping is a vulnerable position, and their wakefulness may be what kept their family name running.

A study of the Hadza people’s sleep patterns headed by David Samson, Associate Professor in the Department of Anthropology at the University of Toronto Mississauga, shows that one or more of the Hadza people were awake (or in the light stages of sleep) for 99.8% of the time.

“We discovered that all subjects were simultaneously scored as asleep for only 18 [minutes] in total over 20 days of observation,” Samson says.

So it seems there is a theory which explains why teenagers stay up late and wake late, whereas their grandparents go to bed early and rise early. If we were all living together, like we used to and some still do today, biology trained us to stagger our sleeping a bit for the household’s protection.

This then leads us into the “grandmother hypothesis,” a theory that states women live far past their premenopausal years because of their vital role in human evolution. If Grandma was the one keeping families growing, thriving, and surviving, natural selection may have began preferring older and older women through the generations. Which, subsequently, would have been passed along to the men in the family.


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Hawke’s findings show it wasn’t always the grandma caring for the family by means of foraging for older, weaned children either. Sometimes, it was a distant relative, aunt, friend or older sibling.

“People often try to explain the fact that humans are so good at cooperating by saying, well, we needed to cooperate in order to succeed at big game hunting, or so that men in one group could bond with other men to go wipe out that neighboring group,” Sarah Hrdy, primatologist at U.C. Davis,  tells NPR. “What that doesn’t do is explain why these traits emerge so early.”

Hrdy is referring to the intricate social traits we see in infants not long after birth, including: sharing, clapping, and reacting to others’ demeanor by way of their facial expressions or emotions.

Unlike other ape species who sometimes won’t let others around their young for months at a time, humans allow other humans around their newborns right at or shortly following birth. Not only that, but humans are the only great apes who allow others to help or be around our babies while feeding.

Our ability to empathize and sympathize with others, pick up on certain social cues, feed each other, or put our heads together for the sake of the common cause is unique — and attributed to an infant’s will to eat and survive, along with Grandma’s willingness to pick up the slack and take over when needed to see her family thrive.

So the next time you send your kids home with Grandma and they come home (pre-dinner), sugared up with their bellies full, don’t take it so personal. They can’t help it — blame evolution.