"The HLA genes that the Neanderthals and Denisovans had, had been adapted to life in Europe and Asia for several hundred thousand years, whereas the recent migrants from Africa wouldn't have had these genes," said study leader Peter Parham from Stanford University School of Medicine in California.
"So getting these genes by mating would have given an advantage to populations that acquired them."
The sway that poorly understood biology has in the nature-nurture debate is indicative of a society that basically doesn't give a shit about equal opportunity. If all you look at is genetics, then of course, that is the only causation you will find.
And, apparently Peter Parham of Stanford thinks that Native Americans are a different, and primitive species:
"Peter Parham suggested a parallel could be drawn between the events of this period and the European conquest of the Americas.
"Initially you have small bands of Europeans exploring, having a difficult time and making friends with the natives; but as they establish themselves, they become less friendly and more likely to take over their resources and eliminate them."
1'Neanderthal sex boosted immunity in modern humans' - BBC News UK