Scientists at Harvard University have claimed that most of the genes believed to be linked to intelligence may not probably be related to the trait at all.
In their research, the scientists found that in nearly every case, the hypothesised genetic pathway failed to replicate. In other words, intelligence could not be linked to the specific genes that were tested.
“It is only in the past 10 or 15 years that we have had the technology for people to do studies that involved picking a particular genetic variant and investigating whether people who score higher on intelligence tests tend to have that genetic variant.
“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,” Christopher Chabris, a team member, said. The problem, Chabris said, was that early technology for assaying genes was very expensive, meaning that such studies were typically limited to, at most, several hundred subjects, who would take IQ tests and provide DNA samples for testing.
As part of their study, the scientists relied on several pre-existing data sets — a massive study of Wisconsin high school graduates that began in the 1950s, the Framingham Heart Study, and an ongoing survey of all twins born in Sweden — to expand that subject pool from a few hundred to many thousands.
“What we want to emphasise is that we are not saying the people who did earlier research in this area were foolish or wrong. They were using the best technology they had available. At the time it was believed that individual genes would have a much larger effect,” Chabris said.