Human brain took great leap forward, gene study finds
By Ronald Kotulak
Chicago Tribune
Posted
December 30 2004
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
vast computing power 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 U. of C. geneticist Bruce Lahn. "There is some justification for
that."
The dark side of this magnificent gift is that some of
the genes that make for a bigger and better brain may also be the ones
that predispose people to mental disorders and addiction.
Learning more about what happens when these genes go wrong could lead to new prevention strategies and treatments.
Reporting inWednesday's issue of the journal Cell, Lahn and colleagues
Eric Vallender and Steve Dorus found that 17 brain-building genes
mutated at a tremendously rapid rate in humans, compared with the
brains of chimpanzees, macaque monkeys, rats and mice.
In a
species that was social and cooperative but had few other survival
skills, being smarter meant a lot to early humans, Lahn said. 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.
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.
The findings, Lahn said, disprove the
contention of other scientists who say the evolutionary process leading
to the bigger human brain was simple adaptation to change -- like
growing bigger antlers, longer tusks or gaily colored feathers.
"We've proven that there is a big distinction," he said. "To accomplish
so much in so little evolutionary time -- a few tens of millions of
years -- requires a selective process that is categorically different
from the typical processes of acquiring new biological traits."
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