Aug 30, 2012 - Health + Traits

Back to School Smarts and Genetics

Editor’s note: This post has been edited from the original to reflect changes in our product.

If you want to stir up trouble, start talking about genetics’ role in intelligence.

First, there’s the 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?

Complex Traits

Not to be glib, but understanding intelligence – how to measure, define, and figure out what can influence it – takes some brainpower. It’s complicated. Innumerable factors influence intelligence – a layered mix of biology and environment. Access to education, your economic well-being, and even the prevalence of parasites in your community impact IQ scores.

That said, there’s good evidence that some differences in measurable intelligence, such as your IQ score, can be chalked up to genetics. While IQ tests don’t consider essential 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.

IQ Score Not Always the Right Measure

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 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 surrounding this one measure of intelligence. By the way, there will be a test—actually, three of them—in this series of posts.

Genetic Factors

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 is associated with “performance IQ” (i.e., nonverbal IQ). Each A at increased subjects’ performance IQ by an average of three points compared to those with no copies. The authors estimated that this accounts for 3.4% of the variation in performance IQ between people.

While the association between differences in IQ scores is significant, its overall effect is minimal, a difference of just three points on average.

It’s also important to note that no single gene has an inordinate impact on IQ scores. Instead, hundreds of genes 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 was also associated with a very slight increase in IQ. We wrote about this in the Blog in April.

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