Study finds genes play role in intelligence

Previous studies involving twins and adopted children have indicated that genes do play an important role in intelligence, perhaps accounting for about half the variation among individuals. But the relative contributions of genetics and environment remain controversial, and it has been unclear how much of a factor genes are. And scientists have been frustrated in their attempts to identify specific genes that may be involved in IQ.

In the new analysis, the researchers calculated that indeed perhaps 40 percent to 50 percent of individual differences in intelligence - both how much someone knows and how good they are at problem-solving - are due to genetic variations. But it appears that the differences in intelligence are due to many genes, each playing a small role. That means it will be difficult, if not impossible, to ever identify any genes that play a major role in IQ, the researchers say.

Nevertheless, the study “is the first that finds that a substantial proportion of the genetic contribution suggested by’’ earlier “studies can be found in signals in people’s DNA,’’ Deary wrote.

Eric Turkheimer, a psychologist at the University of Virginia, called the findings unsurprising.