The whole post is worth reading, but the money shot:
The central point of the paper is exceedingly simple. Haldane demostrated in 1927 that the fixation probability of a single copy of a new adaptive allele is 2s. This means that if archaic humans had any alleles that would have been adaptive for modern humans, it would take only a very small amount of interbreeding for modern humans to pick up these alleles, with a near-100 percent likelihood.
Greg Cochran has more. Obviously this work builds upon the Lahn introgression paper. Instead of crude species typologies the data is now pointing to a more complex set of relations between gene lineages.
