One of the peculiarities of American discussion about race is that skin color is assumed to be synonymous with racial distinctions. That is, skin color is not just a trait, but it is the trait which defines between population differences. There’s a reason for this, the skin is the largest organ and it is very salient. Populations with little phylogenetic relationship to each other, from India to the Pacific to Southeast Asia have been referred to as “black” by lighter-skinned populations. No population is referred to by their neighbors as those “straight hairs,” to my knowledge. But another point in the United States is that historically the black-white dichotomy has dominated our historical narrative to the exclusion of others. (with an asterisk for Native Americans) Though black Americans are an admixed population, which is around 20% European in ancestry with considerable variance (e.g., ~10% of the black American population is more than 50% European by ancestry), white Americans are relatively homogeneously European. Unlike the populations of Latin America admixture did not occur along a continuum, and due to hypodescent there was a categorical binning where black Americans with any visible African ancestry were categorized as non-white (and some with no visible African ancestry!). But the past is not the present. Today Americans of Latin American origin are a larger proportion of the population than black Americans. These groups are often admixed in ancestry, and exhibit a continuum of appearance. The mean proportions of ancestry can also vary from region to region, as evidenced by the recent paper I pointed to earlier this week. While black Americans and white Americans are nearly disjoint in physical appearance, there are Latinos of all phenotypes. Most understand that the quasi-racial status of the Hispanic/Latino category is awkward, and at some point the old paradigm will need to shift. Not only is the United States transitioning to beyond a black-white model but we also now understand the genetics of human pigmentation. The genes which are responsible for most of the variation between human populations in complexion have been identified, including their effect sizes. About half a dozen genes of large effect can explain ~90% of the between population variance. Some of the genes, such as SLC24A5, are so ancestrally informative that sans selection you can ascertain ancestry in mixed populations simply by inspecting its frequency.
