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Smaller Brain, Better Intelligence?

February 7, 2011

Puzzled scientists are debating if the shrinking brains of humans is a sign we are growing dumber or that evolution is making the key motor leaner and more efficient.

The average size of modern human brains has decreased about 10 percent during the last 30,000 years — from 1,500 to 1,359 cubic centimeters, the size of a tennis ball, reports the AFP news agency.

The brains of females, which are on average smaller than those of men, have also experienced an equivalent drop in size. These measurements were taken using skulls found in Europe, the Middle East and Asia.

“I’d called that a major downsizing in an evolutionary eye blink,” John Hawks of the University of Michigan told Discover magazine. Other anthropologists however, note that brain shrinkage is not surprising as the stronger and larger we are the more gray matter we need to control this larger mass.

The Neanderthal, a cousin of the modern human who disappeared about 30 millennia ago was far more massive and had a larger brain. The Cro-Magnons were the Homo sapiens with the biggest brain. They were also stronger than their modern descendants.

David Geary, a psychology professor at the University of Missouri reports these traits were necessary to survive in the hostile environment of the distant past. He has studied the evolution of skull sizes 1.9 million to 10,000 years old as our ancestors and cousins lived in an increasingly complex social environment.

Using population density as a measure of social complexity, Geary and his colleagues hypothesize that the more humans are living closer together, the greater the exchanges between groups, the division of labor and the rich and varied interactions between people.

Finding that brain size decreased as population density increased, Geary tells AFP, “As complex societies emerged, the brain became smaller because people did not have to be as smart to stay alive.”

Downsizing however does not mean modern humans are dumber than their ancestors — instead, they developed more sophisticated forms of intelligence, said Brian Hare, an assistant professor of anthropology at Duke University. He noted that the same phenomenon can be observed in domestic animals compared to their wild counterparts.

Huskies may have smaller brains than wolves, but they are smarter and more sophisticated. Huskies can understand human communicative gestures, behaving similarly to human children.

“Even though the chimps have a larger brain (than the bonobo, the closest extant relative to humans), and even though a wolf has a much larger brain than dogs, dogs are far more sophisticated, intelligent and flexible, so intelligence is not very well linked to brain size,” Hare explained to AFP.

Humans have characteristics from both the bonobo and chimpanzee, which is more aggressive and domineering. “The chimpanzees are violent because they want power, they try to have control and power over others while bonobos are using violence to prevent one for dominating them,” Hare continued.

“Humans are both chimps and bonobos in their nature and the question is how can we release more bonobo and less chimp.”

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