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Believe it or not, the size of the human brain has become
smaller over the past 20,000 years. Scientists argue over whether this means we
are becoming more or less intelligent as a species.
“I'd call that a major downsizing in an evolutionary
eye blink (眨眼),”
John Hawks told Discover magazine.
Why is the brain becoming smaller?
There are different theories to explain it. One is that tens
of thousands of years ago, before the decline began, to survive in cold and
dangerous conditions, humans needed a stronger and larger body and therefore, a
larger head. Also they had to chew the tough meat of rabbits, foxes and horses.
As conditions improved, the brain stopped growing, according to supporters of
this theory.
Another theory comes from a recent study by David Geary and
Drew Bailey. They found that brain size decreased as population density(密度) increased.
“As complex societies appeared, the brain became smaller
because people did not have to be as smart to stay alive.” Geary told AFP.
But smaller brain size does not necessarily mean that modern
humans are less smart than their ancestors. “Modern humans simply developed
different, more complex forms of intelligence,” said Brian Hare.
Hare's studies focus on two types of great apes: chimpanzees
and bonobos. Both are much like humans, but are physically quite different from
one another. The bonobo has a smaller brain than the chimpanzee, and is also
much less aggressive and more tolerant.
“When it comes to working out a problem,” Hare said,
“chimpanzees are much less likely to accomplish it if it involves working
together. Not so with bonobos.”
The smaller brain in
modern humans may be evidence that we can cooperate,” Hare told the US National
Public Radio.