In his book Intelligence and How to Get It, Richard Nisbett makes a big deal out of the ancestry research to show that the black deficit in IQ is not due to genes. He argues that if genes explain the black-white IQ gap, then blacks with more white ancestry should be smarter, but then claims the research doesn't show that.
I've seen studies that contradict Nisbett, but allow me to weigh in with General Social Survey (GSS) data. The GSS records the race of respondents and also asks them from which country or part of the world did their ancestors come. Almost 90 percent of blacks answer either Africa; their ancestors are American Indian; or they are American only. But a small number give a European country, and the countries most often cited are England, Germany, Ireland, and France. I'm assuming that white ancestors are recent and/or prominent enough to motivate a black person to give this kind of answer.
I calculated mean IQ for both types of blacks (N = 2,231). Those who say their ancestors originally came from Europe have a mean of 97.0, while those who give another answer have an average of 91.2. The difference is statistically significant.
UPDATE: I also found a question about listing one or more races that you consider yourself to be. Those who first mention black, but then list white as a second race have a mean IQ of 96.1. Problem is, it's only 11 respondents.