If you want to stir up trouble, start talking about the role genetics plays in intelligence.
First there’s the whole question of what you’re talking about: Is intelligence measured through mathematical skills, problem solving, perceiving emotions, or a raw score from an I.Q. test?
Not to be glib but understanding intelligence — how to measure it, how to define it, and figure out what can influence it — takes some brainpower. It’s complicated. There are innumerable factors that influence intelligence — a layered mix of biology and environment. Access to education, your economic wellbeing and even the prevelance of parasites in the community you live in impact IQ scores.
That said there’s good evidence that a percentage of the differences in measurable intelligence, such as your IQ score, can be chalked up to genetics. While IQ tests don’t take into account important life skills — things like your powers of persuasion, or your ability to build consensus and feel empathy — the tests are valuable nonetheless. At the very least your IQ score is a pretty good predictor for how well you’ll do in school.
As Richard Haier, of the University of California at Irvine, said to Carl Zimmer in a Scientific American article, IQ score doesn’t tell you everything about how smart someone is.
But it’s like many other measurements that can be useful in the right context.
“When you go see your doctor, what’s the first thing that happens? Somebody takes your blood pressure and temperature,” Haier said. “So you get two numbers. No one would say blood pressure and temperature summarize everything about your health, but they are key numbers.”
So as we begin a series of “Back to School” posts, we’re going to take a moment to look at the genetics around this one measure of intelligence. By the way, there will be a test — actually three of them — in this series of posts.
As for measures of intelligence, recent studies estimate that in early childhood about 25-to-40 percent of individual variation in measurable intelligence can be attributed to genetics. In adults, this number increases to about 80 percent.
A study of Dutch families found that the SNP rs363050 is associated with “performance IQ” (i.e. non-verbal IQ). Each A at rs363050 increased subjects’ performance IQ by an average of three points compared to those with no copies. The authors estimated that rs363050 accounts for 3.4% of the variation in performance IQ between people.
While the association between rs363050 and differences in IQ scores is significant, its overall effect is very small, a difference of just three points on average.
It’s also important to note that there is no single gene that has an inordinate impact on IQ scores. Instead there are hundreds of genes that impact intelligence with a cumulative impact on IQ scores. In a recent study researchers found another variant, this one in the HMGA2 gene, that also has a small effect on IQ scores.
Although the HMGA2 gene has been associated with height, it also influences the size of the brain. Researchers also found that the C version of rs10784502 was also associated with a very slight increase in IQ. We wrote about this in the Spittoon in April.