While the general consensus within the psychological community is that IQ is primarily genetic, a recent study suggests that the majority of genes that were previously believed to have been correlated with intelligence, or "g," as that which IQ is intended to measure is known, still has a long ways to go. The researchers looked at 12 genes which had previously been associated with IQ in a recent study and found that virtually none of the genes could be shown to be correlated with IQ in subsequent tests. In the words of one of their scientists.
"It is only in the past 10 or 15 years that we have had the technology for people to do studies that involved picking a particular genetic variant and investigating whether people who score higher on intelligence tests tend to have that genetic variant...In all of our tests we only found one gene that appeared to be associated with intelligence, and it was a very small effect. This does not mean intelligence does not have a genetic component, it means it's a lot harder to find the particular genes, or the particular genetic variants, that influence the differences in intelligence."
In other words, the technology is still relatively young, and we still likely have a long way to go. The researchers suggest that, although IQ may be comparably genetic to a trait like height, in both cases, it is extremely difficult to pin down exactly which genes are correlated with both, because rather than being the result of a single, easily identifiable mutation or variant, these traits are the cumulative effect of mutual genes. The researchers believe that the reason for this high degree of false positives is because of how expensive early genetic testing was, which forced the scientists to use a sample size that was way too small for studying something as polygenic as the genetic basis of intelligence. Indeed, these studies oftentimes included only a few hundred subjects, which is laughably small for such a subject.
Those who had been originally involved in these studies, the researchers say, believed that there were a few identifiable genes, each of which would be responsible for differences in IQ by several points. This assumption, they say, was misguided. The approach they used is known as the 'candidate gene' approach. According tot his approach, genes are studied which are already correlated with a known biological function. The researchers had conjectured that those who possessed such genes and scored highly on IQ tests must have had as the root of their high IQ, those genes.
The recent study suggests that at least some of the dozen genes examined may indeed play a partial role in intelligence, but that this role may be very small, and may dependent upon a complex and poorly understood interaction with other genes. The researchers believe that there may be thousands of genes and gene variants correlated with intelligence. They suggest that a trait like high IQ may be the result of a complicated intra-gene interaction as well as a complicated gene-environment interaction.
Harvard University. (2012, February 24). In the genes, but which ones? Studies that linked specific genes to intelligence were largely wrong, experts say. ScienceDaily. Retrieved July 1, 2014 from www.sciencedaily.com/releases/2012/02/120224140506.htm