Study draws link between helpless babies and human intelligence

From an evolutionary standpoint, oneof 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 tobe. 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 journalProceedings 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 developmentcompared to other primates, in order to accommodate their large brains. Brain size relative to body size in infancy iscorrelated 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 thenvoila 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'talert and can't cling to their mothers at birth.

The theory suggeststhis helplessnessstarts 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 aneven 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.

• Celeste Kidd talks to Quirks & Quarks May 28 at noon on CBC Radio One

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 brainsize relative to body size at birthas well as the age at which the babies were weaned - a measure of helplessness, since babies require less parental care after weaning.

"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 latera 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 beto nurture them.

Why do we only find this type of intelligencein 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 distinctionwith humans, for starters, is that we are mammals.We give birth to live young.

Somefairlyintelligent species like the octopus, for example, simply lay eggs so there isn't the samekind ofselection for intelligence. Their intelligence took a lot longer to evolveand hasn't achieved the levels seen in humans.

• Inky the octopus's tenacious escape reveals intelligent, soulful creature

That's the keythe live birthand this obstetric dilemma, whichgave 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 reportedAlbert Einstein had a comparatively small brain yet he was a once-in-a-lifetime genius. So this isone potential flaw in the theory that intelligence comes down to cranium size. But if we consider Einstein anoutlierin 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'msmarter than my parents' generation?

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 sixmillion years ago with Australopithecus species.This is thehominingroupthat 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 shiftto 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 whichencouraged more learning, and thus more brain capacity.

• Sliced raw meat may have played key role in human evolution

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 yesand 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 Kiddabout 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."