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 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 is associated with “performance IQ” (i.e. non-verbal IQ). Each A at increased subjects’ performance IQ by an average of three points compared to those with no copies. The authors estimated that accounts for 3.4% of the variation in performance IQ between people.While the association between 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 was also associated with a very slight increase in IQ. We wrote about this in the Spittoon in April.
  • “It’s also important to note that there is no single gene that has an inordinate impact on IQ scores.”

    Not exactly accurate, given how many single gene disorders cause drastically reduced IQ. But normal variation in IQ is determined by many genes. It’s like with height – the mutation for achondroplasia drastically affects height, but most genes affecting height only have a small impact.

  • Mike Biegner

    Linking intelligence with genetics has been tried since the turn of the 20th century, when IQ tests were used to link certain ethnic groups with intelligence. IQ is a socially constructed measurement. There are stories of immigrants coming to this country having never seen an electric light in the early 20th century, being shown pictures of a light bulb and having no idea what it was. It is true that certain genetic conditions, like Down Syndrome, or Rhett syndrome, have a genetic basis and as a result can impact cognitive development. But the greatest predictor of outcomes in schools is not IQ tests, but early intervention. Intellect has a plasticity which is not predetermined by genes. genes have less to do with success than socioeconomic background, and early intervention.