Genetics: The more we see, the less there is

In the concluding chapter of my forthcoming book (link), I look at the evidence for an alcoholism gene.  My research showed that the more powerful our tools become, the less we find in the way of genetic causality.  Modern genetic research has wiped away any basis for the idea that alcoholism is a genetically transmitted disease.  The most that can be said is that some people appear to inherit a lower responsiveness to alcohol, so that if they drink, they must drink more to get the same high.  For details, see my book, due out in April.  

Now comes an article in Scientific American, by science journalist Carl Zimmer,  reporting on modern research into the genetics of intelligence.  Here too, the conventional wisdom has been that genes play a major role.  But when the most powerful computer-assisted research tools are turned on the human genome, the supposed genetic factor all but evaporates.  Intelligence turns out to depend very weakly on a diversity of genes. The most influential of these genes contributes just 0.4 per cent (less than one half of one per cent), and this gene is believed to influence also a variety of other cell functions -- so that it is not specific to intelligence as such.  

Much of the myth of genetic causality rests on twin studies.  This is true both in alcoholism and in intelligence research, as well as in other fields (for example, autism).   Zimmer cites research showing that twin studies involving affluent families show a strong apparent genetic influence, while similar studies involving twins from poorer families show virtually no genetic factor at work.  The modern molecular genetic studies suggest that the apparent genetic influence reported in some twin studies may be a chimera due to false methodological assumptions.   Twin studies have been severely criticized, and some scientists consider them junk.  The SciAm article is in the October 2008 issue at p. 68; a link is (temporarily) here.