The differential biology reader

Johnson et al look beyond heritability:

The heritability of human behavioral traits is now well established, due in large measure to classical twin studies. We see little need for further studies of the heritability of individual traits in behavioral science, but the twin study is far from having outlived its usefulness…Twin samples continue to provide new opportunities to identify causal effects with appropriate genetic and shared environmental controls.

To understand why heritability estimates are no longer important, it is necessary to understand that they are completely dependent on the specifics of the samples and environmental conditions from which they are take…This means that little can be gleaned from any particular heritability estimate and there is little need for further twin studies investigating the presence and magnitude of genetic influences on behavior.

Johnson et al ask that we unpack the C of the ACE model rather than just focusing on the additive genetic variance. Components of variance only get us so far in building up causal stories of psychological differences. They argue that twin studies are still useful for teasing apart environmental causation from individuals' inherent dispositions to choose different environments.

None of this should be controversial, although it needs to be said. However, how much of this is a symptom of seeing the world through only one model? I think this is what Greg Carey is getting at with the Bouchard Prize:

Perhaps the major reason for abandoning C and E is that they have operated as taken-for-granted, set-piece structures that have prevented us behavioral geneticists from thinking deeply about the environment.

In other models for estimating heritability, such as the animal model, there is nothing sneaky about specifying other environmental effects exactly, such as those from identifiable early rearing conditions. The problem, as always, is having enough data to get good estimates of these effects. Of course, evolutionary biologists and animal breeders will always be interested in exact values of h².

Johnson et al. Beyond heritability: twins studies in behavioral research. Current Directions in Psychological Science (2009) vol. 18 (4) pp. 217-220

Carey. The environment in behavioral genetics research.

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