A new study finds that most of the specific genes long thought to be linked to intelligence probably have no bearing on one’s IQ.
As Homer Simpson might say, “Doh!”
Furthermore, researchers say that it may be some time before researchers can identify intelligence’s specific genetic roots.
In the study, Christopher Chabris of Union College and David Laibson, a Harvard economist, analyzed a dozen genes using large data sets that included both intelligence testing and genetic data.
In nearly every case, the researchers found that intelligence could not be linked to the specific genes that were tested.
The results are published online in Psychological Science.
Psychologists have long believed that intelligence, like most other traits, is a combination of innate or genetic predispositions and personal experiences as influenced by our environment. Over the past few decades, emerging technology has allowed researchers a closer look at those genetic underpinnings.
But according to Chabris, “In all of our tests we only found one gene that appeared to be associated with intelligence, and it was a very small effect. This does not mean intelligence does not have a genetic component. It means it’s a lot harder to find the particular genes, or the particular genetic variants, that influence the differences in intelligence.”
It had long been believed, on the basis of studies of identical and fraternal twins, that intelligence was a heritable trait, and this study supports that theory. But older studies that picked out specific genes were flawed, Chabris said, primarily because of technological limits that prevented researchers from probing more than a few locations in the human genome to find genes that affected intelligence.
“We want to emphasize that we are not saying the people who did earlier research in this area were foolish or wrong,” Chabris said.
“They were using the best technology and information they had available. At the time, it was believed that individual genes would have a much larger effect — they were expecting to find genes that might each account for several IQ points.”
Chabris said additional research is needed to determine the exact role genes play in intelligence.
“As is the case with other traits, like height, there are probably thousands of genes and their variants that are associated with intelligence,” he said.
“And there may be other genetic effects beyond the single gene effects. There could be interactions among genes, or interactions between genes and the environment.
“Our results show that the way researchers have been looking for genes that may be related to intelligence — the candidate gene method — is fairly likely to result in false positives, so other methods should be used.”