Many mysteries about human origins will be solved thanks to the advent of full genome sequencing. Hammer et al. found archaic admixture in Africans on just 61 genomic regions, each about ~20kb in length.From LiveScience via Razib:
I'm willing to bet that once scientists turn their attentions to full genomes, they will have substantial and indisputable evidence for genetic divergence between stretches of human DNA that simply too deep to be explained in a conventional Out-of-Africa timeframe.
If there was substantial archaic admixture in Africa c. 35ka, according to Hammer et al.'s estimate, and coinciding with the (intrusive?) appearance of Upper Paleolithic modern humans such as Hofmeyr, then full genome sequencing will provide the smoking gun evidence for it. Such an event would simultaneously solve many mysteries about the African population, such as its apparent higher effective population size, greater allele diversity, and recombination rate.
Our species might have also hybridized with a now-extinct lineage of humanity before leaving Africa, according to findings this year from Hammer and his colleagues. Approximately 2 percent of contemporary African DNA might have come from a lineage that first diverged from the ancestors of modern humans about 700,000 years ago. For context, the Neanderthal lineage diverged from ours within the past 500,000 years, while the first signs of anatomically modern human features emerged only about 200,000 years ago.
Hammer noted that he and his colleagues were very conservative with their analysis, only looking for lineages that diverged even more from modern humans than Neanderthals. "It's possible there may be others we can detect that are more closely related to modern humans," Hammer told LiveScience.
"We've probably just scratched the surface of what we might find," Hammer added. "We only looked at a small number of regions of the genome. This coming year, you'll see a lot of progress made with full genome data. This year, we should be able to confirm what we found and go way beyond that."I started talking about "Afrasians" mixing it up with "Palaeoafricans" as a major cause for African genetic diversity back in 2005. From a 2006 treatment:
It is clear that the small early modern human population must have inhabited a correspondingly small geographical region, so it is not surprising that in their movements within Africa they would have interbred with the pre-existing humans. After all, humans lived in Africa for a long time before the emergence of the moderns, and there is no reason to believe that all the African branches of humanity were wiped out to be replaced by the advancing moderns.
I predict that in the coming years, we will learn much more about the different strata of genetic ancestry contained in Africans, as well as Europeans and East Asians. Note, also, that there is no candidate for the source population of the archaic contribution of West Africans. This, again, is not surprising, because western Africa has a much less advantageous climate than eastern Africa for bone preservation, in addition to being less well researched. Even in Europe, where anthropological science is the oldest, and cave surveys have been numerous, there are still only a handful of well-preserved Neanderthal specimens. Hopefully, some of the archaics of Africa remain to be discovered.Some of these archaics have indeed been found.
All indications point in the direction that the Afrasian/Palaeoafrican theory is about to be confirmed. I purposefully decided to name the major recent component in our species' ancestry "Afrasian", because I did not want to take a strong stand on where this component originated (Africa or Asia). My reticence to jump on the recent Out-of-Africa bandwagon with both feet, seems to have been well-justified, as Out-of-Arabia seems to be an increasingly strong possibility: from the LiveScience piece, once again:
"I hope that our findings will stimulate research in South Asia — India in particular — to find the remains of early anatomically modern humans in that part of the world,"archaeologist Hans-Peter Uerpmann from Eberhard Karls University in Tubingen, Germany, told LiveScience.
"Our focus this year will be on gathering evidence to reconstruct the paleoclimate in southern Arabia during the ice age that lasted between 75,000 and 60,000 years ago," paleolithic archaeologist Jeffrey Rose at the University of Birmingham in England told LiveScience. This will help researchers determine how friendly or hostile the climate was back then "to help understand the fate of these early humans on the Arabian Peninsula."
If these ancient peoples eventually died off in Arabia, they would just be a failed migration out of Africa. However, if they survived, they may be the ancestors "to all non-African people living on Earth," Rose said. "Only further exploration throughout Arabia will answer these questions."These Middle Stone Age inhabitants of Arabia may not just be the ancestors only of everyone outside Africa, but of many within Africa itself.