With sleepless nights and puzzling crying spells, caring for a newborn may seem like a mind numbing endeavor. But the mental abilities needed to keep a helpless, fussy infant alive may actually be the source of our smarts.

Humans’ extraordinary intellectual abilities may have arisen, in part, in an evolutionary feedback loop involving the care of helpless infants, researchers hypothesize in a study published in the Proceedings of the National Academy of Sciences. In the loop, big-headed babies are born relatively early in their development to ensure that they fit through the human vaginal canal. The underdeveloped newborns then rely heavily on the savviness of their parents for survival. Through generations, this selects for brainy parents, which pushes kids to have ever fatter noggins and, thus, earlier births.

“Human infants are born far more immature than the infants of other species,” study author Celeste Kidd, a brain and cognitive science researcher at the University of Rochester, said. “For example, giraffe calves are able to stand-up, walk around, and even flee from predators within hours of their births. By comparison, human infants cannot even support their own heads.”

The authors caution that the theory doesn't explain all of humans’ exceptional smarts, which is off the charts when compared to our closest relatives. There are a lot of other factors that likely contributed, such as social learning, diet, language, and the general development of reasoning skills seen in other primates. “The model is not intended as a full account but rather as a piece of a much more complex evolutionary and reproductive history in which multiple traits are interrelated,” write Kidd and her co-author, Steven Piantadosi, a cognitive scientist also at Rochester.

To back up their hypothesis, the pair made a mathematical model of basic elements of childcare and intelligence development to see how they might relate. The model accounted for things like infant and adult head size, adult pelvic size—which may have been constrained by evolutionary pressure for bipedalism—survival of childbirth, intelligence, and overall mortality. The researchers found that the model predicted a runaway selection for higher intelligence.

Next the researchers looked for correlations in other primates, particularly looking at weaning age, which can act as a proxy for maturity at birth, with the more immature newborns weaning at an older age. The researchers found a clear connection with intelligence: the older the weaning ager, the smarter the primate.

Though the hypothesis may only be one factor in the evolution of human intelligence, the authors speculate that it offers a satisfying explanation as to why humans became super smart and not other creatures, such as some insects and reptiles that have had a lot more time to evolve. The key may be the link between live birth and large brains, the authors say. More research and comprehensive analysis will be needed to validate the author's hypotheses.

Proceedings of the National Academy of Sciences, 2016. DOI: 10.1073/pnas.1506752113 (About DOIs).