Study draws link between helpless babies and human intelligence

From an evolutionary standpoint, one of the most baffling features of human babies is just how helpless they are. But a new study suggests the more helpless the baby is, the smarter it can grow up to be. CBC Radio science columnist Torah Kachur explains why.

Being born helpless lets human babies have bigger brains, makes for smarter parents

Human babies may be born earlier in their development than other primates to accommodate their bigger brains. (iStock)

From an evolutionary standpoint, one of the most baffling features of human babies is just how helpless they are. 

Here is a potential future Nobel laureate or world leader or sports hero who can't even hold his or her head up.

But a new study suggests the more helpless the baby is, the smarter it can grow up to be. CBC Radio science columnist Torah Kachur explains why.

How does a baby's helplessness connect to intelligence later in life?

That's what a new study in the journal Proceedings of the National Academy of Sciences (PNAS) aims to figure out. The researchers believe one way we can explain the fact that humans are really the only species to have developed sophisticated intelligence is because our children are born earlier in development compared to other primates, in order to accommodate their large brains. Brain size relative to body size in infancy is correlated with intelligence.

The theory goes like this: if you need a larger brain for increased intelligence, that poses a problem in gestation because of the so-called "obstetric dilemma." Or as moms know it — searing, blinding pain. Because at some point, it's simply not feasible for a large head to pass through our narrow pelvis. 

So the solution is to have your baby earlier in its development, so that both mother and infant survive the birth and then — voila — you give birth to a child with a bigger brain relative to its body.

But that makes the baby more helpless because the rest of the baby's body hasn't developed to the same level of maturity as other primates like bonobos. Human babies, unlike bonobos, aren't alert and can't cling to their mothers at birth.

The theory suggests this helplessness starts what's called a positive feedback loop. When you have helpless infants, the parents need to be even smarter to ensure their baby's survival.

This means infants from less intelligent parents don't survive, making the population even smarter on average through natural selection. Which leads to an even larger head size, which leads to an even smarter population. 

Repeat that for a few million years, and you get the level of intelligence seen only in humans.

How do you test for a theory like this?

Celeste Kidd, from the University of Rochester, was one of the authors of the study.

She said they looked at 23 different primate species, and administered what she described as a sort of "primate-appropriate I.Q. test." They linked the results to brain size relative to body size at birth as well as the age at which the babies were weaned - a measure of helplessness, since babies require less parental care after weaning.

This graph, from the University of Rochester, shows a correlation between the time spent weaning an infant and relative intelligence in different primate species. (
"It turns out that weaning time is a really excellent predictor of primate intelligence across all these other primate species," she said.

In short, the trend was that the later a species weans its young, the more intelligent it is.

The results gave them very clear data that intelligence is something that was selected for over and over and over again, partly because the more helpless the infant, the smarter parents have to be to nurture them.

Why do we only find this type of intelligence in humans?

This model and theory helps explain that.

There's no doubt there are very intelligent creatures that share our planet. We may marvel at an elephant's memory or a chimp's tool use, but it's not the same as inventing the electronic device you're reading this on.

The distinction with humans, for starters, is that we are mammals. We give birth to live young.

The University of Rochester's Celeste Kidd is the co-author of a new study that draws a link between the helplessness of human infants and intelligence. (
Some fairly intelligent species like the octopus, for example, simply lay eggs — so there isn't the same kind of selection for intelligence. Their intelligence took a lot longer to evolve and hasn't achieved the levels seen in humans.

That's the key — the live birth and this obstetric dilemma, which gave fuel to the fire of runaway selection for intelligence to arise so quickly in human evolution.

Is brain size the only way to measure intelligence?

It's been reported Albert Einstein had a comparatively small brain — yet he was a once-in-a-lifetime genius. So this is one potential flaw in the theory that intelligence comes down to cranium size. But if we consider Einstein an outlier in the spectrum of brain size to intelligence, the average still holds. 

And more importantly, the brain size-to-body ratio is important. Clearly, a blue whale has a larger brain than us, yet we are certainly considered more intelligent by most metrics.

Does this mean I'm smarter than my parents' generation?

Skull reconstructions of Australopithecus afarensis and Paranthropus boisei. It's believed the shift to a larger cranium started about six million years ago with Australopithecus species. (University of Utah/Handout via Reuters)
Maybe. But that's a lot harder to test because of the subtle shifts in I.Q. in such a small time. 

We're really talking about changes over a few million years — in evolutionary time, a very short period for humans to acquire the incredible intellectual abilities over our closest cousins.

The prevailing hypothesis is that the shift to a larger cranium and more human-like head proportions started about six million years ago with Australopithecus species. This is the hominin group that the famous fossil Lucy was a member of. 

That's likely when the shift started — why and how that started is still very unclear, but one thing the new model says is that once there's some environmental shift to select for intelligence, there's a relatively rapid shift to smarter and smarter babies. 

That environmental trigger has been hypothesized to have been everything from increasing meat in the diet from hunting, to the increased dependence on larger groups and more social interaction — which encouraged more learning, and thus more brain capacity.

Does this mean we'll see babies born earlier, with larger heads, in the future?

You might think so. But there's going to be a point where the rest of the organs, like the lungs, haven't developed to the point where the baby can survive after birth.

That raises an interesting point — does the rise in C-sections possibly allow for more runaway evolution and increased brain size?  The answer is yes and no. 

Even if a baby has a head the size of a watermelon and couldn't be birthed naturally, the other organs have to be mature enough for survival. So a world of six-month gestation in humans is unlikely. 

I asked Celeste Kidd about that. She said it needs further study — and admitted we don't have all the answers yet.

"I have a little list of things that I don't know, that I should know more about," she said. "I'm adding that."


Torah Kachur

Science Columnist

Torah Kachur has been the syndicated science columnist for CBC Radio One since 2013. Torah received her PhD in molecular genetics from the University of Alberta and studied how worm gonads develop. She now teaches at the University of Alberta as a contract lecturer in cell biology and genetics.