Can any depiction of genetic relationships among humans allow simultaneously for similarity, diversity, ancestry, and admixture (i.e., groups that had split mixing again)? I asked this question while puzzling over the messages conveyed by the following diagram from the work of Tishkoff and collaborators on genetic variation among humans in and out of Africa.
The first message from the diagram is that there are many more branches leading from the ancestral within-Africa human population to current African groups than there are to groups in the rest of the world, that is, to groups derived from people who migrated out of Africa at some point after 100,000 years ago. This branching pattern suggests that, if we were to divide human genetic diversity into a small number of groups of similar diversity, say, five groups, then most of these groups would be African. (Indeed, four would be from Africa and the fifth would be a combination of an East African group and the non-African groups.) This finding seems to discredit the genetic reality of traditional races, where “traditional” has varied greatly but in general separates Africans, Asian, Australian, and Europeans or “Caucasians”.
There are other messages, however. The diagram places the non-Africans out on the right, taking up 40% of the horizontal scale, and colored lighter, all suggesting that the rest of the groups can still be lumped together. I wonder if someone who promotes (or promoted) a traditional racial classification would be at all troubled by learning that their African race was really a collection of 13-14 races. If they had the idea that something special genetically happened in the branch that left Africa, then those groups left in Africa are united in lacking that something.
This series of posts present some of my explorations of alternative depictions of human genetic variation keeping my initial question in mind. By the end of the series I will have prepared the ground for an assertion that the very methodology of generating and depicting human ancestry privileges a racialized view of human diversity.
The exploration begins in the next post by looking at rearrangements of the horizontal ordering in the diagram.