This post by Neurocritic, Bad News for the Genetics of Personality, is going to get a lot of play. The boy-king of the cognitive neuroscience blogosphere has already smiled upon it, and extended the analysis a bit. The short of it is that

one needs to be very skeptical of the idea large effect QTLs in personality genetics.

In the post the Neurocritic reviews a paper, A genome-wide association study of Cloninger's Temperament scales: Implications for the evolutionary genetics of personality, which performed a genome-wide association, and found basically nothing despite a large sample size. I'm not that surprised as genomicists I know have expressed lots of skepticism of previous work in this area. The implication here is that personality may be like height or I.Q., having a genetic component, but not one whose genetic architecture is easy to elucidate with current methods. Both the Neurocritic and the boy-king raise the issue of whether personality tests really measure anything. I have asked psychologists about this particular point before. Something like the Big Five personality traits are fun, but often strike me as parlor games. I haven't gotten a very clear answer on the validity of these personality tests, though I probably haven't asked anyone whose bread & butter was this particular area. The high heritability of personality traits suggests to me that the tests are measuring something consistently; if the results were random one wouldn't see correlations within the family. I mooted my concerns and Jason Goldman pointed out that the tests may be consistent in measuring something, but may not measure what they purport to measure. The boy-king quotes a psychologist who attempts to reconceptualize how personality plays out:

This led Mischel to construct a new metaphor for human personality. While modern psychology still clung to a model of personality rooted in the humors of the ancient Greeks – we were born with a certain amount of choleric temperament and that was it – Mischel proposed a model of personality called interactionism. One of his favorite metaphors for interactionism concerns a car making a screeching noise. How does a mechanic solve the problem? He begins by trying to identify the specific conditions that trigger the noise. Is there a screech when the car is accelerating, or when it’s shifting gears, or turning at slow speeds? Unless the mechanic can give the screech a context, he’ll never find the broken part. Mischel wanted psychologists to think like mechanics, and look at people’s responses under particular conditions.

This is all fine,

but this does not negate that people have different dispositions, all things equal.

Additionally, even with non-linear gene-environment interactions there may be a genetic component of variation (though it wouldn't show up as narrow sense heritability). I guess I'll have to look at what Mischel says in detail, but the idea makes me even more confused and muddled as to personality. The primary aim of the post is to foster and encourage discussion. I'm curious what David Dobbs, Jason Goldman, Daniel MacArthur, etc. think. If you're a psychologist or psychiatrist I'm curious as to your opinion.