It’s what happens to your brain after you’re born that makes you human.

Jason Hill and colleagues were comparing the structure of newborn brains to those of adults when they came upon a striking find, documented this week in the Proceedings of the National Academy of Sciences. Clearly, the brain expands greatly as you grow from baby to adult. But the researchers discovered not only that the brain grows in a non-uniform way, but also that the parts of the brain that change most rapidly as people grow up are the same parts that changed the most as humans evolved away from our primate relatives.

The research revealed that brain regions involved in higher cognitive and executive processes—such as language and reasoning—grow about twice as much as regions associated with basic senses such vision and hearing…. “The parts of the [brain] that have grown the most to make us uniquely humans are the same regions that tend to grow the most postnatally,” Hill said [National Geographic].

But why would we be born with brains more like those of the apes? At birth, more basic abilities like the physical senses are more important for survival, the researchers say. Study author David Van Essen also hypothesizes that it could be advantageous for those brain regions to grow once you’re out of the womb, allowing, for instance, the extraordinary capacity of children to pick up language.

Lastly, there’s the more practical side of the birth process:

The limitations on brain size imposed by the need to pass through the mother’s pelvis at birth might also force the brain to prioritize, said study researcher Dr. Terrie Inder, professor of pediatrics at Washington University School of Medicine [LiveScience].

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