How helpless babies make humans so smart
This may come as a surprise to anyone who has ever glimpsed a comments section, but humans are smarter than we need to be.
Natural selection can only explain so much about our intelligence. Community living, hunting in groups, survival in harsh environments — these adaptations helped us live and reproduce and they unquestionably demanded bigger brains, so we evolved to meet the challenge. But they don’t explain how we got smart enough to develop differential calculus and write epic poetry.
“Other species had similar challenges and had much longer to develop human-like intelligence but didn’t,” said Steven Piantadosi, a cognitive scientist at the University of Rochester. “So why aren’t those animals the ones flying airplanes and landing on the moon?”
The answer just might have to do with how pathetic we are when we’re born. Helpless infants need smart parents to take care of them, and intelligent parents need bigger brains. But giving birth to offspring who will develop big brains is a challenge, because the mechanics of getting a big head out of a mother’s body are, well, difficult. That means babies need to be born at an earlier stage of development, before their heads get too big — when they’re even more tiny and helpless.
In a study published Monday in the Proceedings of the National Academy of Sciences, Piantadosi and colleague Celeste Kidd modelled how this evolutionary positive feedback system could have led to runaway natural selection that resulted in absurdly smart humans.
The effect was surprisingly strong: “The comparative helplessness of the species was a stronger predictor of intelligence than almost any other factor,” Piantadosi said.
He and Kidd tested their theory on humans’ primate relatives. Using a common measure of intelligence established by primatologists — “it’s basically a primate IQ test,” Kidd said — they cross-referenced each species’ smarts with its weaning time (how long infants rely on their mother’s milk). The relationship was immediately obvious.
Marmosets, which are clever but not exactly brilliant, wean their young after just a few months. But young chimpanzees, which can learn language, use tools and perhaps even mourn their dead, depend on their mothers for nearly four years.
But whereas even baby bonobos can grab on to their mothers as soon as they are born, human infants can’t grasp, walk or even lift their heads.
“Human babies are exceptionally useless,” Kidd said. With a laugh, she amended her adjective use: “I mean, helpless.” And though humans are weaned relatively young, children still rely on their parents a lot longer than other creatures’ babies. As Kidd pointed out, a 3- or 4-year-old would fare very poorly on its own in the wild — which bonobos do all the time.
This relationship makes sense if you think about the kinds of thinking humans are good at, according to Piantadosi.
We excel at social reasoning — interpreting others’ motivations and intentions and figuring out how to act accordingly. Existing theories about human intelligence have attributed this to our communal lifestyles: the fact that we live and hunt in groups, and our need to communicate through language.