Genes and Intelligence

Over the years, researchers have unlocked several mysteries about intelligence, taking us closer and closer to discovering the truth behind this "ability," this "property of the mind."

One of the mysteries that scholars are unlocking or are trying to unlock is the link between genetics and human intelligence. 

In 1998, Robert Plomin, PhD and his collaborators published a study which suggests that a variation in the gene for IGF2R, a multifunctional protein receptor for a human growth factor, was linked to exceedingly high SAT scores.

The IGF2R was responsible for only a small amount of discrepancy in the test scores, about 2 percent, but the findings implied that scientists were a step closer to explaining differences in intelligence as caused by our biological make up.

The following year however, Plomin and his collaborators published a follow-up study in Psychological Science (Vol. 13, No. 6) that did not reflect their initial findings.

This just shows how difficult it is to try to link intelligence, which is so complex a trait that it is likely influenced hundreds of genes, to a lone gene. It also shows the environment and the complex cultural landscape in which such as study is conducted.

Plomim however, still thinks that there is strong evidence that genetics could explain the variation in intelligence among people.

Studies on twins showed that most inherited differences in cognitive ability may be the result of a variation in one, "overachieving" factor of intelligence known as g, says Plomin.

Researchers have recently shown that IQ scores are related to the measure gray matter in particular parts of the brain. This finding suggests that g is "more than just a statistical construct."

"It suggests that g isn’t just some artifact of the cognitive tests that we administer, but it actually exists in the brain," says Plomin.

Dennis Garlick, PhD, a psychologist at the University of Sydney, however, warns that this "well-validated" breakthrough may not be all that.

"Finding the specific genes for intelligence is merely confirming what we already know existed," says Garlick. "It is still a long road from identifying the genes responsible for intelligence to actually understanding what they do, and hence understanding how intelligence is inherited."

Plomin concurs that understanding how genes for intelligence work is crucial.

Plomin and his collaborators worked on a project to find an animal model that could be used to look at how genes influence intelligence. The team have tested 500 genetically diverse mice on a number of cognitive tasks and discovered that as with humans, a large portion of the variation among mice can be explained by differences in g.

"If we find a gene that’s associated with g in humans, we want to then find out if that gene is associated with some cognitive process, or with g, in mice," says Plomin. "The name of the game is functional genomics–understanding how genes work."

However, some researchers like Douglas Wahlsten, PhD, a University of Alberta mouse researcher, question whether mouse and human intelligence are really comparable.

"I certainly would not use the term intelligence to describe what we are measuring with our mazes," says Wahlsten. "The relation between mouse genes that alter learning and possible genes that alter human IQ remains to be explored."

Source: APA