The Flynn Effect on IQ begs the whole question of correlation and genetics.

The Flynn Effect is a rate metric that exists outside of point-time measurements of IQ, and thus gives us another insight into what is going on.

http://johnhawks.net/weblog/reviews/brain/intelligence/flynn_1999.html

Quote
"Both Black and White American soldiers fathered children with German women, and the IQ scores of both groups of children were almost identical. Flynn argued that direct evidence of this kind, reflecting what actually occurs when different races are subject to qualitatively similar environments, is more important than the kind of indirect evidence that comes from attempting to correct samples for socioeconomic status or other environmental variables.

In addition to this kind of direct evidence, Flynn argues here that the observation of IQ test gains over time further reduces the relevance of the indirect evidence of environmental differences. For one, the gain of IQ from one generation to the next must certainly be almost all, if not entirely, due to environmental change. Flynn presents this as a real-world example that fits Lewontin's model, above, where within-group differences are mostly genetic, while between-group differences are mostly environmental in origin. (This also plays into a continuing current theme in Flynn's research examining how IQ can continue to increase while remaining fairly strongly heritable. This itself appears paradoxical, since continued environmental gains would normally be expected to reduce the heritability by decreasing potential environmental variance.) Second, the magnitude of the IQ gains is so large, that the Black-White average IQ difference seems comparatively minor (15):

As for the environmental gap one must posit to explain the Black-White IQ gap, IQ gains over time pull this out of the stratosphere and down to earth. It appears that Blacks have enjoyed a slightly higher rate of gain on Wechsler-type tests than Whites (Herrnstein and Murray 1994, pp. 277, 289). This implies that since 1945, Blacks have gained at an average rate of over 0.30 points per year and have gained a total of 16 points over 50 years. Therefore, the Blacks of 1995 should have matched the mean IQ of the Whites of 1945. Therefore, an environmental explanation of the racial IQ gap need only posit this: that the average environment for Blacks in 1995 matches the quality of the average environment for Whites in 1945. I do not find that implausible."