MARY LOUISE KELLY, HOST:
Man the hunter, the classic hypothesis is that men hunting to feed mates and offspring was a quintessential step in the evolution of our species. Some think it may have led to group cooperation, advanced tool use and extra protein to fuel bigger brains. A newer theory claims that what made us human might have had less to do with men out hunting and a lot more to do with what was going on at home.
As part of an NPR-wide series, How to Raise a Human, NPR's John Poole explains.
JOHN POOLE, BYLINE: Kristen Hawkes is an anthropologist at the University of Utah. She tries to figure out our past by studying modern hunter gatherers, like the Hadza, who live in the East African savanna. Groups like this are about as close as we can get to seeing how our early human ancestors might have lived.
KRISTEN HAWKES: So here's an opportunity to see, well, OK, here are people living on wild foods with all these big animals that they're hunting. And so let's see what happens.
POOLE: Hawkes and her colleagues kept track of how much food everyone was bringing home. She says when they track the success rates of individual men...
HAWKES: They almost always failed to get a big animal. The average hunter was successful 3.4 percent of the days.
POOLE: So if you're picking a way to feed the kids...
HAWKES: Well, if the kids were relying on this for dinner tonight, they'd be in trouble night after night after night after night after night after night.
POOLE: So if Dad wasn't bringing home the bacon, who was? The women. For starters, mom was keeping the family fed by digging tubers. Food is scarce in these savannas and how successful she was at gathering correlated with how big her kid was, until she had another baby.
HAWKES: And then that relationship went away and then the correlation was with their grandmothers.
POOLE: Which must have been kind of mind-blowing.
HAWKES: Which was mind-blowing.
POOLE: Mom and Grandma were keeping the kids fed, not man the hunter. Sarah Hrdy is a primatologist at UC Davis, who also studies connections between child rearing and human evolution.
SARAH HRDY: An ape that produced such costly, costly, slow-maturing offspring as we have could not have evolved unless mothers had had a lot of help.
POOLE: Hrdy says there was another big change happening on the home front. If young kids were being fed by people besides mom, she thinks over evolutionary time, this is what led humans to be so socially oriented, to care so much about the thoughts and intentions of other people.
HRDY: 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 we needed to cooperate so that men in one group could bond with other men to go wipe out the neighboring group. What that doesn't do is explain why these traits emerge so early.
POOLE: She's talking about advanced social traits that we can see even before babies begin walking, like pointing, sharing, paying attention to social cues like smiling and frowning.
MICHAEL TOMASELLO: And then when I thought about it more, I thought, well, wait a minute, you know, why are these little kids doing this?
POOLE: That's Michael Tomasello. He's a developmental psychologist at Duke University in the Max Planck Institute. He originally assumed this early social orientation was preparing kids for skills they'd need as adults, following the man the hunter theory. But after years of comparing cognitive differences between babies and apes, he agrees that these cooperative traits could have evolved to help babies adapt to having multiple caregivers.
Tomasello says other apes don't show anywhere near the level of interest in the sharing behaviors that emerge so early in humans.
TOMASELLO: Humans as individuals aren't that much cleverer than other apes. It's the fact that we can put our heads together with others and communicate and collaborate and learn from others and teach others. Human children are adapted for cooperation and shared intentionality in ways that apes aren't.
POOLE: It's this ability to put our heads together that may have allowed humans to survive, thrive and spread across the globe. While the men were out hunting, grandmothers and babies were sharing food, cooperating and developing new social relationships, perhaps building the foundations of our species' success. John Poole, NPR News.
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