I'll admit it: I am confused about genetics and heritability. Not about the results of the various twin studies - Scott summarises them as "~50% of the variation is heritable and ~50% is due to non-shared environment", which seems generally correct.
But I am confused about what this means in practice, due to arguments like "contacts are very important for business success, rich people get much more contacts than poor people, yet business success is strongly correlated with genetic parent wealth" and such. Assuming that genetics strongly determines... most stuff... goes against so many things we know or think we know about how the world works. And by "we" I mean lots of different people with lots of different political views - genetic determinism means, for instance, that current variations in regulation and taxes are pretty unimportant for individual outcomes.
Now, there are many caveats about the genetic results, particularly that they measure the variance of a factor rather than its absolute importance (and hence you get results like variation in nutrition being almost invisible as an explanation for variation in height), but it's still hard to figure out what this all means.
Then we have Scott's latest post, which points out that "non-shared environment" is not the same as "nurture", since it includes, for instance, dumb luck.
However, "heritable" is not the same as as "nature", either. For instance, sexism and racial prejudices, if they are widespread, come under the "heritable" effects rather than the "environment" ones. And then it gets even more confusing.
Widespread prejudice is not "environment". Rarer prejudice is.
For instance, imagine that we lived in a very sexist society where women were not allowed to work at all. Then there would be an extremely high, almost perfect, correlation between "having a Y chromosome" and "having a job". But this would obviously be susceptible to a cultural fix.
Obviously racial effects can have the same effect. It covers anything visible. So a high heritability is compatible with genetics being a cause of competence, and/or prejudice against visible genetic characteristics being important ("Our results indicate that we either live in a meritocracy or a hive of prejudice!").
Note that as prejudices get less widespread, they move from showing up on the genetic variation, to showing up in the environmental variation side. So widespread prejudices create a "nature" effect, rarer ones create a "nurture" effect. Evenly reducing the magnitude of a prejudice, however, doesn't change the side it will show up on.
Positional genetic goods: Beauty... and IQ?
Let's zoom in on one of those visible genetic characteristics: beauty. As Robin Hanson is fond of pointing out, beautiful people are more successful, and are judged as more competent and cooperative than they actually are. Therefore if we have a gene that increases both beauty and IQ, we would expect it's impact on success to be high. In the presence of such a gene, the correlation between IQ and success would be higher than it should objectively be. This suggest a (small) note of caution on the "mutation load" hypotheses; if reducing mutation load increases factors such as beauty, then we would expect increased success without necessarily increased competence.
But is it possible that IQ itself is in part a positional good? Consider that success doesn't just depend on competence, but on social skills, ability to present yourself well in an interview, and how managers and peers judge you. If IQ affects or covaries with one or another of those skills, then we would be overemphasising the importance of IQ in competence. Thus attempts to genetically boost IQ could give less impact than expected. The person whose genome was changed would benefit, but at the (partial) expense of everyone else.
Do people know of experiments (or planned experiments) that disentangle these issues?