The not-so-smart human

The human species is extraordinarily intelligent. We build cities, explore space, produce amazing art and technology, and tell stories. Although humans are not nearly as old as many other species, we have accomplished more than any of our predecessors in many ways. They do not eat us; we eat them. We even conduct scientific research on them and are considering the possibility of resurrecting some of the extinct ones. However, there is an odd catch to our intelligence: our infants are some of the world's dumbest—or, more accurately, the most defenceless—people. Within an hour of birth, a newborn giraffe can stand, and on its first day of life, it may even be able to escape from predators. A monkey can hold onto its mother to provide shelter and food. A human infant can’t even hold up its own head.

That is the claim made by Kidd and Piantadosi in their most recent work, which was released in a PNAS issue. They contend that the reason humans become so brilliant is because human infants are so defenceless; the one requires the other. Although shocking, the hypothesis is not wholly original. For a considerable amount of time, scientists have been considering the characteristics of human birth and its evolutionary relevance. Humans are members of the group of animals known as viviparous mammals, which give birth to their offspring alive. This implies that while babies must develop inside the body to the point of maturity in order to be born, they cannot become too large to be able to emerge. This leads to a trade-off: the more intelligent an animal is, the larger its head generally is, but the birth canal imposes an upper limit on just how large that head can be before it gets stuck. The brain, therefore, must keep maturing, and the head must continue growing, long after birth. The more intelligent an animal will eventually be, the more relatively immature its brain is at birth.

However, there are a few fascinatingly converging bits of data. One reason for this could be that there is a natural correlation between intellect and live birth because non-viviparous species have not developed to the same degrees of intelligence. Furthermore, there is some evidence in modern humans that suggests parents who are brighter are more likely to have offspring that survive. Even after adjusting for age, education, and a host of other variables, there was a negative correlation found between maternal I.Q. and child mortality in a small sample of 222 Serbian Roma women. In 1978, the number of years of schooling was associated with the infant death rates in a larger sample of parents in California. Global epidemiological studies suggest a decrease in mortality that equals between seven and nine per cent for each year of a mother’s education. None of this is decisive, of course, but it is suggestive.

So, Kidd and Piantadosi formed a hypothesis based on their research. There are incentives for babies to arrive early due to the correlation between intellect and head size. But the cycle might actually be driven by the relationship between IQ and weaning time. Because the physiology of live delivery dictates that a baby's brain has a limited size at birth, you have to be smarter in order to care for more helpless creatures, which means you need a larger brain. This means that new-borns must enter the world at an even more helpless stage of development. Thus, the cycle never ends.

Maybe dumb babies at first, but shortly after, oh so smart.