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Human brain grew rapidly

RONALD KOTULAK:

The first study of genes that build and operate the brain shows that humans underwent a unique period of rapid brain expansion that endowed them with a special form of intelligence not shared by any other animal, according to University of Chicago researchers.

The colossal leap forward grew the human brain to three or four times the size of that of a chimpanzee — man's closest genetic relative — when body sizes are equalized. That pushed human intelligence over the threshold of basic instincts and into an unparalleled realm of cognition, self-awareness and consciousness.

"We tend to think of our species as categorically different, being on top of the food chain," said University of Chicago geneticist Bruce Lahn.

"There is some justification for that."

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Genetic mutations that enhanced intelligence amid the pressure to survive were quickly passed on to future generations. Those not possessing the new genes eventually died off.

Once started, the selection of brain-building genes snowballed, resulting in thousands of changes to thousands of genes in a relatively short period, Lahn said.

"Humans evolved their cognitive abilities not due to a few accidental mutations, but rather from an enormous number of mutations acquired through exceptionally intense selection favoring more complex cognitive abilities," he said.

Lahn, also a Howard Hughes Medical Institute investigator at the University of Chicago, argues that the evolutionary forces that led to the big brain continue to act on humans today and are likely to produce better brains in the future.