A few months ago I was thinking a fair amount about the Neandertals. One issue which became more stark to me due to that particular finding, that a few percent of the human genome seems to have derived from Neandertal populations, is the reality that genetic distinctiveness can persist long after cultural coherency is no longer a reality. That made me reconsider one of the facts of contemporary scholarship, that the Amerindian populations of the two most populous nations of the New World, the United States of America and Brazil, have disappeared or been totally marginalized demographically.
I’ve observed before it looks like that about 15-20% of the ancestry of the Argentine population is Amerindian, despite the nation’s proud identity as a European settler offshoot (i.e., more like the United States or Australia, than Mexico, which has an explicit hybrid identity). But I realized that Brazil was perhaps the bigger catch.
Only 0.4% of Brazilians identify as Amerindian. That’s about 700,000 people. But we know that a substantial number of white, brown and black Brazilians have Amerindian ancestry. Assuming for argument’s sake that the 700,000 Amerindians have undiluted indigenous ancestry, how much of the distinctive Amerindian genome in modern Brazil is to be found in this segment of the population?
There was a paper which came out in an obscure Brazilian journal last year which can help answer this question, DNA tests probe the genomic ancestry of Brazilians. For the purposes of the paper they needed to find a small number of ancestrally informative markers which would allow them to partition the ancestries of the individuals in their data set into European, African, and Amerindian, segments. Luckily these are three very distinctive populations. They cross-checked the utility of their markers against the HGDP data set. In other words the precision and accuracy of the 40 markers they selected should be assessed by how well they can distinguish these three “pure” populations. Their Brazilian subjects consisted of self-identified whites from various regions, as well as black men from Sao Paulo. Brazil’s racial taxonomy has a brown (pardo) category which is large, but judging from the very high proportion of African ancestry among the blacks in their sample I don’t think they included self-identified mixed-race people in that group (some scholars lump mixed and black Brazilians together into the black category).