Human brains 'shrinking over last 20,000 years

Updated on: Tuesday, January 04, 2011

Admit it or not, people may be becoming increasingly dumb, says a new study which has found that the human brain has been gradually shrinking over the
last 20,000 years.
According to the study, this decrease in size follows two million years during which the human cranium steadily grew in size, and it has happened all over the world, to both sexes and every race.

"Over the past 20,000 years, the average volume of the human male brain has decreased from 1,500 cubic centimetres to 1,350 cubic centimetres, losing a chunk the size of a tennis ball. The female brain has shrunk by the same proportion," the
'Daily Mail' quoted as saying a report in 'Discover' magazine.

In the magazine, author Kathleen McAuliffe reported on the comments made by Dr John Hawks, an anthropologist from the University of Wisconsin, who argues that the fact the size of human brain is decreasing doesn't necessarily mean people's
intelligence are in decline as well.

Some paleontologists agree with this diagnosis, that human brains may have become smaller in size, but increasingly efficient. But others believe man has indeed become steadily more stupid as he has evolved.

Several theories have been advanced to explain the mystery of the shrinking brain. One is that big heads were necessary to survive Upper Paleolithic life, which involved cold, outdoor activities.

A second theory is that skulls developed to cope with a chewy diet of rabbits, reindeer, foxes and horses. As our food has become easier to eat, so human heads have stopped growing, according to supporters of this theory.

Other experts say that with high infant mortality, only the toughest survived -- and the toughest tended to have big heads. Therefore a gradually decreasing infant mortality rate led to proportionate decrease in the human brain size.

A recent study conducted by David Geary and Drew Bailey, cognitive scientists at the University of Missouri, explored how cranial size changed as humans adapted to an increasingly complex social environment between 1.9 million and 10,000 years ago.

They found that when population density was low, such as during the majority of human evolution, the cranium increased in size. But when a certain area's population changed from sparse to dense, human cranium size decreased.

They concluded that as increasingly complex societies emerged, the brain grew smaller because people didn't have to be as smart to stay alive.

Human brains 'shrinking over last 20,000 years

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