Separate analyses of genetic markers from the mitochondrial genome, the Y chromosome, and autosomes have revealed that all humans are descended from a small group of ancestors that lived in eastern Africa. In the 22 February 2008 issue of Science, Li et al., in a paper titled “Worldwide human relationships inferred from genome-wide patterns of variation”, have taken this analysis to a much more detailed level.
Li et al. examined 642,690 single-nucleotide polymorphisms in the autosomes of 938 individuals representing 51 populations from all over the world. Their analysis was based on the proposition that each person’s genome originated from K different ancestral populations. They performed the analysis with K = 2 through K = 7. With K = 7, they found that the seven components corresponded to populations from Africa, Middle East, Europe, Central/South Asia, East Asia, Oceania, and the Americas. Individuals from the Middle East displayed the most mixed ancestry; Palestinians, for example, displayed ancestry from South/Central Asia, Europe, and the Middle East.
The researchers created a maximum likelihood phylogenetic tree from the 51 populations. The sub-Saharan African populations appeared nearest the root of the tree, which was established by the chimpanzee branch, consistent with the hypothesis that humans first appeared in Africa and then migrated to the other continents. The two most distant branches of the tree represented the populations from Oceania and from the Americas.
The large number of markers allowed the group to distinguish finer differences among the populations. For example, the eight European populations sampled in the study — Adygei (an ethnic group from the Russian Caucasus), Basque, French, Italian, Orcadian, Russian, Sardinian, and Tuscan — were well separated in a principal component plot.