I can think of many potential ones, but not sure what you have in mind (I also suspect the distinction varies from place to place or time to time).
If there are heritable differences between races, mixed-race people should have scores that proportionally track their ancestry. This gives you, among African Americans and Hispanics in general, a correlation between skin color and intelligence, because more European ancestry will mean lighter skin. We can reverse that relationship to suggest that lighter skin color means more European ancestry. Except among siblings--there, which sibling is lighter or darker is random and not related to overall degree of European ancestry.
(Siblings do vary in their genetic inheritance--that's why they're not twins--but because intelligence is highly polygenic and skin color is only mildly polygenic (determined by about 7 genes), knowing that one sibling has lighter skin tells you almost nothing about whether they're more or less European than another sibling.)
So one can consider a sample of mixed-race people (which almost all non-recent immigrant African Americans in the US are) and compare the within-family and the between-family relationship between skin color and intelligence / social outcomes.
What I've seen on this thinks the evidence is inconclusive but favors the heritability theory (that it's the genetic effect, rather than the visual effect, that drives intelligence and outcomes).
There seems to be something else going on here, and I'm not sure what (saw a talk by some expert guy in that field, that boiled down to him not being sure why either).
This seems to me like it's likely explained by a handful of factors like the following:
People don't capture all of the gains they produce, but those gains do show up somewhere.
Similarly with the benefits of catastrophe avoidance. If smarter people get into fewer accidents, that both reduces their insurance premiums (if insurance companies are able to detect and use that info) and everyone else's insurance premiums, because they're less likely to get rammed.
and thinks the evidence is inconclusive
Grrrrr.... Ok, I'm definitely shifting to the "the field is complicated and the results are uncertain" meta-position on genetics. Still on the "genes are pretty important" side, but no longer willing to rule out environmental explanations (even shared environment is important, apparently, when comparing between countries).
This seems to me like it's likely explained by a handful of factors like the following:
Yes, explanations aren't hard to find. But I would be at least a little bit wary of ...
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?