Surely any characteristic that has been created or optimized by natural selection must be highly heritable.
That's not true. On the contrary, heritability is defined as the part of the observed variation in a trait that is due to genetic differences, and if there has been intense natural selection on some trait, it may be that only those organisms with the same favorable genes for that trait have survived it, so that now there is almost no genetic variation at all.
Note that saying that a trait is heritable and that it's determined genetically in some general sense are two very different things. A trait can be under almost exclusive control of genes, with next to zero environmental influences, but if all the organisms of the species have the same relevant genes, its heritability will be zero. For example, humans are clearly genetically predisposed to develop two arms, but the variation in the number of arms is almost wholly environmental -- people lose arms in accidents, wars, etc. much more often than they get born armless due to genetic causes. So if you calculated the heritability of this trait (the number of arms), it would be near zero, and yet it's clearly absurd to say that the number of your arms is not genetically determined.
This is hardly news, but this Guardian article reminded me of it - genes are really overrated, both among unwashed masses, and also here on Less Wrong.
I don't want to repeat things which have been said by so many before me, so I'll just link a lot.
Summary of evidence against genes being important:
Summary of evidence for genes being important:
And there's nothing more. Decades ago, before we had direct evidence of lack of correlation between genes and outcomes, it was excusable to believe genes matter a lot, even if it was never the best interpretation of data. Now it's just going against bulk of the evidence.
And in case you're wondering how could twin studies show high heredity when everything else says otherwise, I have two examples for you.
This one from a critique of twin studies by Kamin and Goldberger:
"A case in point is provided by the recent study of regular tobacco use among SATSA's twins (24). Heritability was estimated as 60% for men, only 20% for women. Separate analyses were then performed for three distinct age cohorts. For men, the heritability estimates were nearly identical for each cohort. But for women, heritability increased from zero for those born between 1910 and 1924, to 21% for those in the 1925-39 birth cohort, to 64% for the 1940-58 cohort. The authors suggested that the most plausible explanation for this finding was that "a reduction in the social restrictions on smoking in women in Sweden as the 20th century progressed permitted genetic factors increasing the risk for regular tobacco use to express themselves." If purportedly genetic factors can be so readily suppressed by social restrictions, one must ask the question, "For what conceivable purpose is the phenotypic variance being allocated?" This question is not addressed seriously by MISTRA or SATSA. The numbers, and the associated modeling, appear to be ends in themselves."
As the final nail in the coffin of heredity studies:
The Body-Mass Index of Twins Who Have Been Reared Apart
We conclude that genetic influences on body-mass index are substantial, whereas the childhood environment has little or no influence. These findings corroborate and extend the results of earlier studies of twins and adoptees. (N Engl J Med 1990; 322:1483–7.)
Or as paraphrased by a certain commenter on Marginal Revolution:
IOWs, the reason why white kids of today are much fatter than white kids of the 50s and 60s is due to genetic influences and environment has little or no influence
To summarize - heredity studies are pretty much totally worthless data manipulation. Once we accept that, all other evidence points for environment being extremely important, and genes mattering very little. We should accept that already.