The recent paper, The Genetic Ancestry of African Americans, Latinos, and European Americans across the United States, brings together a lot of results which 23andMe has been letting slip in bits and pieces over the years. Most of the press coverage has focused on racial dynamics at the level we’re used to talking about today in the United States. White, black, and Latino (of whatever race). But as I told the first author at BAPG a few weeks ago the dynamics among white Americans is probably where their massive data set can shine. You see it in the figure above, which confirms what many have suspected: the states of the inland South have retained a predominant Anglo-American settler population down to the present. This is clear in their very high fraction of people of “British-Irish descent” in 23andMe Ancestry Composition nomenclature. Including the black American population the overwhelming majority of the population likely descends from people were already resident in the future continental United States in 1776 in this region. Additionally, you can tell that these results are not crazy because in the north Indiana has higher fractions than either Ohio or Illinois, which is exactly what you’d expect if you knew something about the demographic histories of these states. Indiana experienced less migration from European populations who were not of settler stock than Illinois (Chicago) and Ohio (Cleveland and Cincinnati). Similarly, Maine’s elevated fraction makes sense since rural Yankees are demographic more dominant in northern New England than they are in the southern states. Finally, the states of the old Yankee Empire of the northern Old Northwest have been totally demographically transformed by the massive waves of migration from Germany and Scandinavia.
The distinction between settler and immigrant Europeans is clear in relation to detectable non-European ancestry:
We find very low levels of African and Native American ancestry in Europeans with four grandparents born in Europe. We estimate that only 0.98% of Europeans carry African ancestry and 0.26% of Europeans carry Native American ancestry. These levels are substantially lower than the 3.5% and 2.7% of European Americans who carry African and Native American ancestry, respectively…Excluding countries that had major and minor ports in the Atlantic with strong connections to the slave trade (namely Portugal, Spain, France, and United Kingdom) and Malta, which has been the site of migrations from Africa and the Middle East, we obtain a data set of 9,701 Europeans, where we find African and Native American ancestry is virtually absent, with only 0.04% of individuals carrying 1% or more African ancestry and 0.01% carrying 1% or more Native American ancestry, within the margins of survey error estimates.
The African admixture in places like the American South is almost all a function of admixture in the first 150 years or so of settlement (the exception might be Louisiana, where Spanish Creoles may have contributed some African ancestry). The historical and genetic data seem to align there. Though the racial caste system in the American South had an early origin, it became progressively more calcified and stationary as the decades progressed. But by the late 19th century when Jim Crow laws were enacted the African admixture in many Southerners was a very distant memory and thoroughly diluted. To gauge the social and demographic import, recall that detection of genetic fragments does not reflect the total genealogy. Many people with ancestors who were black American slaves do not carry any segments from those individuals, while the ones being detected in this study exhibit a relative enrichment.
In the future I would be very curious about exploring the patterns of relationship of the Anglo-American folkways, as outlined in works such as Albion’s Seed and the The Cousins’ Wars. A major problem though is that these are genetically very close to begin with. The first author of the above work suggested to me that they would need the People of the British Isles data set to get good reference populations. Perhaps in the near future that will be feasible.