The actual proportions of ancestry are then given in the bar chart. Here again, you can see the varying amount of European ancestry. It is also confirmed in the bar chart that most of the African ancestry is Central-West African.
You can also see in the bar chart that compared to the European ancestry component, there is much less variation in the different African subgroup components of ancestry -- in other words, there aren't some individuals who have much more Yoruban ancestry and others that have much more Bantu ancestry. This is why we concluded that it is likely that mating patterns in African Americans probably did not strongly reflect actual origins in Africa. And that is also the reason we concluded that because most African Americans appear to have admixed African ancestry, looking only at a single genetic location (e.g. the Y chromosome or mtDNA, as often done by ancestry companies) gives only a narrow picture of the entire ancestry.
Subsequent figures in the paper pretty much reinforce these conclusions.
OK, so that helps. A lot. Here is another question. I want to know what someone with your background thinks about the notion of "race." As a writer, I approach this through the lens of history. I imagine, because of that, I might be missing some things. I want to know, as a geneticist, whether you think of African Americans as a "race?"
I believe it is inaccurate to refer to African Americans as a race or racial group (much as it is similarly inappropriate to refer to Latinos that way) -- unless you move away from the more classical definitions of race. We try to use the term race/ethnicity. There has been a lot of debate about whether genetic variation in the human population is continuous or discrete. From my view, it is both. This is what makes it challenging to create categories.
One question pops out at me. You indicate some suspicion to referring to African-Americans as a "race" but (in some of your research) you support using "race" in terms of collecting med data and disease studies. Is this a case of a definition -- though it may be imperfect, clunky and at times even misleading -- still telling us something? From what I gathered from those articles "race" can be a proxy not just for genetic stuff, but for social phenomenon too (such as access to health care.) Am I seeing that right? Is it correct to say, for instance, "Yes, race is a social construct, but this does not make it meaningless." It still useful to look at "race," for instance, when studying sickle-cell. Perhaps some day, when we have more refined technique, it won't be.
Definitions can indeed be "clunky." I would use the phrase race/ethnicity rather than just race because in common parlance it is a better description. I tend to think that race has been used more in terms of continental origins (Africa, East Asia, Europe, Americas). On that basis, one would not characterize African Americans as a racial group, but rather as an ethnic group. We sort of implied this in the Genome Biology paper. The reason is that African Americans typically have European as well as African ancestry (and possibly other ancestries as well) and are also culturally distinct from Africans. Sort of similar to Latinos - who from a genetic ancestry standpoint can be nearly anything. Hence our use of race/ethnicity.