Is Intelligence A Genetic Trait?

Your DNA, the genetic code that underlies everything from your eye color to a propensity for diabetes, can have a measurable impact on your intelligence. However, the relationship isn't as simple as inheriting a few genes and instantly becoming a genius. In reality, the links between genetics and intelligence quotient are complicated, and a person's environment may also have a large impact on top of any genetic baseline.

Part of the problem with linking genes to intelligence is that no one quite knows how to define the concept of intelligence in the first place. IQ tests measure performance over a range of skills, and these skills are controlled by different areas of the brain, not just one. Two common ways of assessing intelligence include determining how well you learn and apply knowledge, and how well you can solve problems you've never seen before, but there may be other components that aren't yet well defined.

Studies done on twins, family members, and the general public have all indicated a link between genetics and intelligence, but the exact genes and mechanisms are still under investigation. A 2011 study published in the journal "Molecular Psychiatry" estimated that 41 percent of the variation in crystallized-type intelligence, which involves the ability to gather and retain learned knowledge, and 51 percent of the variation in fluid-type intelligence, which involves on-the-spot thinking and problem solving, are based on genetics. Furthermore, the researchers noted that the data, which looked at over 3,500 adults and 500,000 genetic markers, strongly suggested that intelligence is governed by many genes acting in concert, and that each gene only has a very small impact on its own.

A few genes have been linked to higher IQ, but the effects aren't always clear. For example, in 2007, researchers from the Washington University School of Medicine in St. Louis found that a gene called CHRM2, which is found on chromosome seven, had a measurable impact on performance IQ. Performance IQ involves a person's ability to score high on tests of visual-motor coordination, spatial perception, logical reasoning, and abstract problem solving. However, the researchers caution that the gene likely interacts with up to 100 others, so having a particular variant won't affect overall IQ unless you also have the proper variants of those other genes, too. This gene also didn't impact verbal skills, which are a separate component of IQ tests.

While the idea that your genes affect your intelligence isn't really under debate, recent research indicates that the genes identified so far may not have as much impact as previously thought. A 2012 paper published in "Psychological Science" found that many of the genes previously linked to IQ, including CHRM2, may not have as strong an impact as believed. The new research does continue to show a connection between genetics and IQ, but the lack of connection with specific genes may mean that the interactions between genes or interactions of genes and environment matter more than previously thought. A study published on "PLOS One" in 2010 offered evidence that epigenetics may influence how much your intelligence-related genes contribute to your overall IQ. Epigenetic changes are alterations of the DNA molecule that affect how your genes are expressed, but which don't alter the specific genetic code itself. These changes, which typically occur during embryonic and early-childhood brain development, include things such as the addition or removal of methyl groups on the DNA strand and the modification of regulatory proteins on DNA.