Genes are necessary, but not sufficient, for heritability

I've discussed heritability quite a bit on this weblog. Over the past 5 years of blogging on genetic topics this is the #1 issue I've been attempting to nail into the heads of readers because it is a concept which is critical in correctly modeling the world around us. It isn't an idea which is in common circulation, as evidenced by the common assertions in the press which go along the lines of "the trait is half genetic" or "the trait is mostly genetic," after reporting the heritability estimate from the original research. Part of the problem is that heritability emerges out of the quantitative genetic tradition, which is really applied statistics. But when we moderns think of genetics, we conceive of the biophysical reality of DNA, and the discrete packets of information that these transmit. When people speak of heritability then it is natural to map those values onto ...