August 9, 2011

New Evidence That Genes Play Role In Intelligence

A study found new evidence that genes play a role in intelligence, but scientists cannot pinpoint exactly which genes are involved.

Scientists have hunted for "intelligence genes" in recent years, and they determined there may be at least 1,000. 

"It's been kind of a shock to the system that it hasn't worked," said psychologist Eric Turkheimer at the University of Virginia, who had no role in the study. "We can't find the effects of any individual genes that are large enough to seem worth worrying about."

A previous study involving twins and adopted children found that genes have a significant influence on differences in IQ scores, producing about half the difference between adults in general.

Scientists have realized that differences in intelligence come from the overall effect of many genes, each with only tiny influence.

The new DNA study said many genes work together to shape intelligence like the different instruments in an orchestra.

The researchers "whether genetic differences that we could test on people's DNA could explain some of the reasons that people have different intelligence test scores,"  I.J. Deary of the University of Edinburgh in Scotland told the Associated Press.

The team did not ID any genes affecting IQ, but they did find a genetic influence that accounts for at least 40 percent to 50 percent of the differences on intelligence test scores in the 3,511 unrelated adults in their study who were tested on knowledge and problem-solving skills.

They focused on over 500,000 places in the participants' DNA and concluded that the overall effect was coming from many scattered genetic differences.

Deary said that future studies will probably need to involve millions of people to detect the genetic effects.

Though the team now knows the proportion of the variation in intelligence that is likely to be a result of genes, they do not know which genes are likely to be most important in determining intelligence.

"If they can be found, and if we want to follow them up, to find out some of the mechanisms that underlie successful thinking, our best guess at present is that the number is huge. It could be many thousands," Deary said in a statement. "That could be a limitation to progress using this type of research."

The researchers reported their findings on Tuesday in the journal Molecular Psychiatry.


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