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Genes thought to affect IQ might not

Oct. 2, 2012
Courtesy of 
the Association for Psychological Science
and World Science staff

Most of the genes long thought to be linked to in­tel­li­gence, simply aren’t, a new study has con­cluded.

“We are not say­ing the peo­ple who did ear­li­er re­search in this ar­ea were fool­ish,” said Chris­to­pher Chabris, a psy­cho­log­i­cal sci­ent­ist at Un­ion Col­lege in New York who co-led the stu­dy. “They were us­ing the best tech­nol­o­gy and in­form­ati­on they had avail­able.”

Nor do Chabris and his col­leagues de­ny that in­tel­li­gence is he­red­i­tary and ge­net­ic. But they say it now turns out that this in­tan­gi­ble qual­ity is probably too com­plex to sum up in a few genes. It may be some time be­fore re­search­ers can iden­ti­fy in­tel­li­gence’s spe­cif­ic ge­net­ic roots, say the re­search­ers, whose find­ings are pub­lished on­line in the re­search jour­nal Psy­cho­log­i­cal Sci­ence.

Chabris and Da­vid Laib­son, a Har­vard econ­o­mist, led an in­tern­ati­onal team of re­search­ers that 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 tested.

“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,” said Chabris.

It had long been be­lieved, on the ba­sis of stud­ies of iden­ti­cal and fra­ter­nal twins, that in­tel­li­gence was a her­it­a­ble trait. The new re­search af­firms that conclusi­on. But old­er stud­ies that pick­ed out spe­cif­ic genes had flaws, 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.

Al­so, “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 ex­plained. IQ is a wide­spread meas­ure of in­tel­li­gence in which av­er­age in­tel­li­gence is scored as 100, while high­er or low­er in­tel­li­gence are scored high­er or low­er. The score is meant to mea­sure a per­son’s in­tel­li­gence as com­pared to the av­er­age for their age group, as a per­cent­age.

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.”


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Most of the genes long thought to be linked to intelligence, simply aren’t, a new study has found. “We are not saying the people who did earlier research in this area were foolish,” said Christopher Chabris, a psychological scientist at Union College in New York who co-led the study. “They were using the best technology and information they had available.” Nor do Chabris and his colleagues deny that intelligence is hereditary and genetic. But they say it now turns out that this intangible quality is probably too complex to sum up in a few genes. It may be some time before researchers can identify intelligence’s specific genetic roots, say the researchers, whose findings are published online in the research journal Psychological Science. Chabris and David Laibson, a Harvard economist, led an international team of researchers that 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 tested. “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,” said Chabris. It had long been believed, on the basis of studies of identical and fraternal twins, that intelligence was a heritable trait. The new research affirms that conclusion. But older studies that picked out specific genes had flaws, 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. Also, “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 explained. IQ is a widespread measure of intelligence in which average intelligence is scored as 100, while higher or lower intelligence are scored higher or lower. 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.”