Exploration 7: Superimposing genetic variation on the ancestry diagram from a simulation
The following picture comes from the same random simulation used in the previous post to generate directions of branching and the distances of each branch from its most recent common ancestor. The two dimensions stand for the genetic variation of the whole set of populations. This time aprons are drawn around the midpoints of the groups A to R at the bottom of the ancestry tree (but not around their ancestors). This shows that the variation of the original population (which would extend about 20% past the largest circle) is reduced after the branchings that have brought us to the present, but there is still great overlap between most groups. In particular, the descendants A and B of the group AB, which branched off early, shows variation that subsumes that in the the rest of the groups.
A careful viewer might notice, however, that there are some circles that do not overlap at all, as if to say these groups share no genetic variation. This is an artifact of my deciding to reduce the variation at each branching enough so that not all the circles would extend beyond the web. In doing so, I realized that I was increasing the ratio of between groups to average within-group variation well beyond what we find in the actual human world.