"Long before it's in the papers"
March 25, 2015


Study ties education, not just genes, to IQ

March 25, 2015
Courtesy of the University of Virginia
and World Science staff

Educa­t­ion—and not just genes—af­fect your I.Q., ac­cord­ing to a study that com­pared the in­tel­li­gence test scores of Swed­ish twins raised in dif­fer­ent en­vi­ron­ments.

The proj­ect com­pared scores of 436 twin brothers of which one was reared by bi­o­log­i­cal par­ents and anoth­er by adop­tive par­ents. The adopt­ees, tested at ages 18 to 20, showed I.Q.’s 4.4 points high­er than their nona­dopt­ed sib­lings, ac­cord­ing to the find­ings. 

The re­search­ers say that’s probably be­cause adopt­ing par­ents tend to pro­vide bet­ter educa­t­ion than bi­o­log­i­cal par­ents. That in turn oc­curs be­cause adop­tion agen­cies can af­ford to be se­lec­tive in choos­ing par­ents with whom to place chil­dren—be­cause would-be adopters out­num­ber avail­a­ble adopt­ees.

The find­ings were pub­lished on­line in the Early Edi­tion of the jour­nal Pro­ceed­ings of the Na­t­ional Acad­e­my of Sci­ences on March 23.

“In Swe­den, as in most West­ern coun­tries, there is a sub­stantial ex­cess of in­di­vid­u­als who wish to adopt com­pared to adop­tive chil­dren avail­a­ble,” said co-author Ken­neth S. Kendler of Vir­gin­ia Com­mon­wealth Uni­vers­ity. “There­fore, adop­tion agen­cies see it as their goal of se­lect­ing rel­a­tively ide­al en­vi­ron­ments with­in which to place adop­tive chil­dren.”

The adop­tive par­ents in the study tended to be both more ed­u­cat­ed and in bet­ter so­ci­o­ec­on­omic cir­cum­stances than the bi­o­log­i­cal par­ents, the au­thors said. In the stu­dy, pa­ren­tal educa­t­ion lev­el was rat­ed on a five-point scale; each ad­di­tion­al un­it of educa­t­ion by the rear­ing par­ents was as­so­ci­at­ed with 1.71 more un­its of I.Q. 

In the rare cases when the bi­o­log­i­cal par­ents were more ed­u­cat­ed than the adop­tive par­ents, the ef­fect was the op­po­site and the adopt­ed off­spring showed the low­er I.Q., the in­ves­ti­ga­tors added.

Pre­vi­ous stud­ies have found that ed­u­cat­ed par­ents are more likely to talk at the din­ner ta­ble, take their chil­dren to mu­se­ums and read sto­ries to their chil­dren at night.

“We’re not de­ny­ing that cog­ni­tive abil­ity has im­por­tant ge­net­ic com­po­nents, but it is a naïve idea to say that it is only genes,” Kend­ler said. “This is strong ev­i­dence that ed­u­cat­ed par­ents do some­thing with their kid that makes them smarter and this is not a re­sult of ge­net­ic fac­tors.”

Co-author Er­ic Turk­heimer, al­so of the uni­vers­ity, au­thored a study in 2003 in­di­cat­ing that the ef­fect of genes on I.Q. de­pends on so­ci­o­ec­on­omic sta­tus. He said the most re­cent study fur­ther af­firms that.

“D­if­fer­ences among peo­ple in their cog­ni­tive abil­ity are in­flu­enced by both their genes and en­vi­ron­ments, but ge­net­ic ef­fects have of­ten been eas­i­er to dem­on­strate be­cause iden­ti­cal twins are es­sen­tially clones and have highly si­m­i­lar I.Q.’s,” Turk­heimer said.

“Many stud­ies of en­vi­ron­men­tal ef­fects on cog­ni­tive abil­ity are based on spe­cial pro­grams like Head Start that chil­dren are placed in for a lim­it­ed amount of time,” he added. “These pro­grams of­ten have pos­i­tive re­sults while the pro­gram is in place, but they fade quickly when it is over. Adop­tion in­to a more ed­u­cat­ed house­hold is the most per­ma­nent kind of en­vi­ron­men­tal change, and it has the most last­ing ef­fects.”

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Education—and not just genes—affect your IQ, according to a study that compared the intelligence test scores of Swedish twins raised in different environments. The project compared intelligence test scores of 436 Swedish male siblings in which one member was reared by biological parents and the other by adoptive parents. The adopted males, tested at ages 18 to 20, showed I.Q.’s 4.4 points higher than their nonadopted siblings, according to the findings. The researchers say that’s probably because adopting parents tend to provide better education than biological parents. That in turn occurs because adoption agencies can afford to be selective in choosing parents with whom to place children—because would-be adopters outnumber available adoptees. The findings were published online in the Early Edition of the journal Proceedings of the National Academy of Sciences on March 23. “In Sweden, as in most Western countries, there is a substantial excess of individuals who wish to adopt compared to adoptive children available,” said co-author Kenneth S. Kendler of Virginia Commonwealth University. “Therefore, adoption agencies see it as their goal of selecting relatively ideal environments within which to place adoptive children.” The adoptive parents in the study tended to be both more educated and in better socioeconomic circumstances than the biological parents, the authors said. In the study, parental education level was rated on a five-point scale; each additional unit of education by the rearing parents was associated with 1.71 more units of IQ. In the rare cases when the biological parents were more educated than the adoptive parents, the effect was the opposite and the adopted offspring showed the lower IQ, the investigators added. “Many studies of environmental effects on cognitive ability are based on special programs like Head Start that children are placed in for a limited amount of time,” said co-author Eric Turkheimer, also of the university. “These programs often have positive results while the program is in place, but they fade quickly when it is over. Adoption into a more educated household is the most permanent kind of environmental change, and it has the most lasting effects.” Previous studies have found that educated parents are more likely to talk at the dinner table, take their children to museums and read stories to their children at night. “We’re not denying that cognitive ability has important genetic components, but it is a naïve idea to say that it is only genes,” Kendler said. “This is strong evidence that educated parents do something with their kid that makes them smarter and this is not a result of genetic factors.” Turkheimer authored a study in 2003 indicating that the effect of genes on IQ depends on socioeconomic status. He said the most recent study further affirms that. “Differences among people in their cognitive ability are influenced by both their genes and environments, but genetic effects have often been easier to demonstrate because identical twins are essentially clones and have highly similar IQs,” Turkheimer said.