See previous post about quotes from the medical genetics and physical anthropology literature on admixture analysis and the causal interpretation. There's quite a few older admixture studies that examined relationships between racial ancestry and intelligence. Most of these used quite crude methods such as interviewer judgement. Some used a better method, namely objectively measured skin tone/color/reflectance. A small few used something approaching modern technology, namely blood groups. Curiously, you only hear about the ones with the smallest samples probably because these found no relationships, and are thus perceived to provide evidence (sometimes seen as conclusive) for non-genetic models. Thus, we can find environmentalists defending this kind of analysis, now that they like the results.