From “Shared Genes With Neanderthal Relatives: Modern East Asians Share Genetic Material With Prehistoric Denisovans” (ScienceDaily, Oct. 31, 2011), we learn:
Our study covers a larger part of the world than earlier studies, and it is clear that it is not as simple as we previously thought. Hybridization took place at several points in evolution, and the genetic traces of this can be found in several places in the world. We’ll probably be uncovering more events like these,” says Mattias Jakobsson, who conducted the study together with Pontus Skoglund.
Previous studies have found two separate hybridization events between so-called archaic humans (different from modern humans in both genetics and morphology) and the ancestors of modern humans after their emergence from Africa: hybridization between Neanderthals and the ancestors of modern humans outside of Africa and hybridization between Denisovans and the ancestors of indigenous Oceanians. The genetic difference between Neandertals and Denisovans is roughly as great as the maximal level of variation among us modern humans.
The Uppsala scientists’ study demonstrates that hybridization also occurred on the East Asian mainland. The connection was discovered by using genotype data in order to obtain a larger data set. Complete genomes of modern humans are only available from some dozen individuals today, whereas genotype data is available from thousands of individuals.