It’s Good to Grow Slow

Why are humans so smart? Because we stay young for so long.

A new study published in the journal Genome Research may hold clues to why we humans have much more prolonged childhoods than other critters. Researchers comparing the brains of humans, chimpanzees and macaques found that genes in the prefrontal cortex, a region of the brain which governs social behavior, delay of gratification and reasoning ability, express themselves differently in humans than in the other animals.

The major difference is pace. In humans, the genes, which control the development and function of the synapses between neurons, are highly active from just after birth until age five; in the chimps and birds, activity begins to tail off soon after birth. Further research showed that while the number of synapses in chimps and macaques peaked shortly after birth, human brains didn’t top out until age four. “Humans have much more time to form synaptic connections,” says lead researcher Phillipp Khaitovich. More synapses mean more brainpower. Even when researchers took into account humans’ longer life spans and generally slower rate of maturation, the different pattern of gene expression was clear.

Neurologist Eric Courchesne of UCAL-San Diego noted that the new study fits well with his research into autism. The brains of autistic children, he says, grow more quickly than normal—leaving them with fewer experiences to draw from in forming vital synaptic connections. The slower the brain wires up, the better, the study seems to say.