Genes & IQ

Carl Zimmer has a post up where he points to a piece he just wrote for Scientific American, Searching for Intelligence in Our Genes. Here's the major point:

Intelligence tests do identify a difference among people that has predictive power, and that difference can be linked-in part-to differences in people's genes.

The news about intelligence is that now scientists have new tools for probing intelligence, from brain scans to gene chips that can search for variations in half a million genetic markers at a time. But so far, those tools are yielding some pretty scant results. For example, just a handful of genes show much sign of influencing intelligence, and yet each one accounts at best for a fraction of one percent of the variation in test scores.

Jason Malloy says in the comments:

I feel like the anti-story here is larger than IQ, and is really about what genome-wide association studies have been able to reveal about continuous traits in general at this stage. I doubt intelligence is very unique compared with other quantitative genetics traits. Height and intelligence, for example are similar in a lot of ways (e.g. similar heritabilities), and we're seeing the same stuff with the genetics of height.

The heritability of height on a modern developed society is on the order of 0.80. There are some studies which suggest IQ might be about the same, though others push it all the way down to the 0.20-0.30 range. As Jason implies it looks like aside from pathological retardation variation in intelligence is due to the mass action of a huge number of loci, just like height. In this skin color has been the exceptional low hanging fruit of quantitative traits, most of the between population variance can be pinpointed to half a dozen genes. In any case, with all that in mind I have suggested an easier way to produce a "designer" high IQ baby even if we don't know the genes implicated in the phenotype....

Related: Linkage versus association: a mini-primer.


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The problem is, of course, that despite heritability estimates such as those you mention, variation in stature in humans at the population level is not genetic. At all (except in a very fewe cases).

How do you know that?

I suspect that the results so far are being (mis-) interpreted as throwing doubt on the substantially genetic basis of general intelligence.

This is a kind of delaying tactic. Or the latest in the series of straws that people have grasped-at in rejecting the implications of heritable IQ differences.

The proper question is not _whether_ genes are a significant influence on IQ (they are, of course!); but of learning, gradually, exactly _how_ genes influence IQ.

Harvard dropped a patent for an genetic IQ test based on Bruce Lahn's research, for political reasons apparently, Lahn then stopped working on that line of investigation.

Possibly the researchers into genetic IQ are minimising the variation in their results by having an unrepresentative sampling made up of the only sort of people who consent to have their genes analysed for high IQ: clever people.