North Vietnam, Lao Cai Province, women from Flower Hmong ethnic group carrying babies on their back, Can Cau market, Bac Ha area, Sapa region, Southeast Asia.
Women from Flower Hmong ethnic group carrying babies on their back in Lao Cai Province, North Vietnam.  Getty Images

How Child Care Made Humans Smart

May 23, 2016

Humans developed much higher order intelligence than other mammals because they needed to look after their young for much longer and much more comprehensively, says an intriguing new study.

"The theory is that we are much more intelligent because our infants are so helpless," says Celeste Kidd assistant professor in the Brain and Cognitive Sciences department at the University of Rochester, New York and one of the authors of the new paper which is available online in the Proceedings of the National Academy of Sciences' Early Edition.

Yes, you read that right: good child care got us to where we are today—at the top of the evolutionary heap.

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How does it work? Basically, the human head is a tricky body part. It's big and vaguely solid and excruciatingly hard to push out of the channel through which it must travel to the outside world. And once the human it belongs to is born, that head still has to grow some more. So the humanoid young, which are born live, are born before their brains are fully developed.

An infant giraffe, for example, is up and walking around wobbily within an hour of its birth. Even with those crazy long skinny legs. A human baby takes at least 5000 times that long.

But if the infant baby spent any more time in the womb in order for its brain to develop to a capacity where it could function autonomously, its head would be too big to exit the premises safely. Thus, it's born still very unformed and needs a lot more hands-on nurturing than a new giraffe.

Read More: Cell-Phone Distracted Parenting Can Have Long-Term Consequences: Study

This kind of intensive child care requires a higher order level of cognitive function. The only human babies that survive are the ones whose parents are intelligent enough to protect their helpless offspring from imminent dangers—cold, cliffs, predators, sharp objects. The babies with not-so-capable parents die and their-not-so-capable genes with them. Thus evolution selects for intelligence.

You could call it "survival of the smartest."

The researchers at Rochester tested their theory by modelling it mathematically (it worked), and by looking at data from other primates. And indeed, the primates who score highest on the intelligence scales have the longest weaning times.

Celeste Kidd—Rochester University Celeste Kidd—Rochester University 

Orangutans and chimpanzees nurse their offspring for almost three years and are the smartest. And yes, humans usually wean their kids earlier than that, but are still providing nutrition for them for many years to come in the form of baby food, mac and cheese and tatertots.

The need to look after helpless children, of course, is not the only pressure that led to human intelligence. But Kidd says her theory makes more sense than some other ideas for why humans developed cognitive ability way above all other species.

"Another set of previous theories about why we are so much smarter than other species have to do with intelligence being an adaptation to difficult environmental circumstances," says Kidd. "But that doesn’t explain why other species that had much longer to evolve and similar environmental circumstances, like reptiles and insects, never developed super-intelligence."

Kidd also notes that humans' intelligence is of a certain type: it's particularly social. "We’re capable of doing very sophisticated social reasoning about the beliefs and knowledge and intentions of others," says Kidd. "And that’s exactly the kind of intelligence that would be very useful for taking care of an infant."

What use is this information to parents? Kidd says this new theory might, as side benefit, help new parents feel better about their life. "When you’re looking down at your newborn and you’re wondering why the universe is doing this to you, you can take solace in knowing that your newborn being very useless is why you’re so intelligent."

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