The figure to the right illustrates a model that is put forward in a new paper, Recovering signals of ghost archaic introgression in African populations. This was originally a preprint, Recovering signals of ghost archaic introgression in African populations. So we’ve discussed the implications extensively. Carl Zimmer has covered the story in The New York Times, while Georbe Busby did so in The Conversation.
Broadly, the results are getting at something which plenty of people have been noticing for many years: when it comes to Sub-Saharan Africans, there is something deeply diverged in West Africans vis-a-vis non-West Africans. These results seem to suggest that the divergence between this outgroup lineage and our own is a bit earlier than the modern-Neanderthal/Denisovan split. There are many abstruse statistical inferences and simulations, and it looks like the reviewers made them do a lot of analyses. But the general result is something other groups have seen as well, so I believe it. Additionally, the admixture of this lineage into West Africans seems to have occurred about 50,000 years ago, suspiciously close to the general expansion of modern humans out of Africa (or the most recent expansion).
From the discussion:
The signals of introgression in the West African populations that we have analyzed raise questions regarding the identity of the archaic hominin and its interactions with the modern human populations in Africa. Analysis of the CSFS in the Luhya from Webuye, Kenya (LWK) also reveals signals of archaic introgression, although our interpretation is complicated by recent admixture in the LWK that involves populations related to western Africans and eastern African hunter-gatherers (section S8) (20). Non-African populations (Han Chinese in Beijing and Utah residents with northern and western European ancestry) also show analogous patterns in the CSFS, suggesting that a component of archaic ancestry was shared before the split of African and non-African populations. A detailed understanding of archaic introgression and its role in adapting to diverse environmental conditions will require analysis of genomes from extant and ancient genomes across the geographic range of Africa.
This work seems more a question than an answer.