There is an interesting article in Science about something once thought to be impossible—the discovery and recovery of ancient DNA in Central Africa:
In the new study, geneticists and archaeologists took samples from the DNA-rich inner ear bones of the four children, who were buried 3000 and 8000 years ago at the famous archaeological site of Shum Laka. The researchers were able to sequence high-quality full genomes from two of the children and partial genomes from the other two. Comparing the sequences to those of living Africans, they found that the four children were distant cousins, and that all had inherited about one-third of their DNA from ancestors most closely related to the hunter-gatherers of western Central Africa. Another two-thirds of children’s DNA came from an ancient “basal” source in West Africa, including some from a “long lost ghost population of modern humans that we didn’t know about before,” says population geneticist David Reich of Harvard University, leader of the study.
The discovery underscores the diversity of African groups that inhabited the continent before the Bantus began to herd livestock in the grassy highlands of western Central Africa. The Bantus made pottery and forged iron, and their burgeoning populations rapidly displaced hunter-gatherers across Africa. Analyzing DNA from a time before this expansion offers “a glimpse of a human landscape that is profoundly different than today,” Reich says.
Here’s the part most interesting to me:
The team compared the children’s DNA to ancient DNA extracted earlier from a 4500-year-old individual from Mota Cave in Ethiopia and sequences from other ancient and living Africans, using various statistical methods to sort out how they all were related, which groups came first, and when they split from one another. The team’s bold new model pushes back Central African hunter-gatherer origins to 200,000 to 250,000 years ago—not long after our species evolved. The model suggests their lineage split from three other modern human lineages: one leading to the Khoisan hunter-gatherers in southern Africa, one to east Africans, and one to a now-extinct “ghost” population.
An early diversification of modern humans fits the great variation seen in fossils of early Homo sapiens, says paleoanthropologist Katerina Harvati of the University of Tübingen, who is not part of this study. The lineages would have parted company and moved off into different parts of Africa 200,000 to 250,000 years ago, preserving their distinctness by only occasionally interbreeding at the boundaries.
IMO the “out of Africa” hypothesis is already teetering on the edge of being disproved and I am one of those benighted souls who believe that the human species is more then 250,000 years old. Making decisions about these things would be facilitated by a more rigorous definition of “species”. When I read about interbreeding between our species, Neanderthals, and Denisovans, it raises my hackles. These are clearly different subspecies not different species. The designation should be Homo sapiens neanderthalensis not Homo neanderthalensis. Heck, I’m still holding out for erectus to be determined to be a localized variant of our species.
Whatever the case, multiple different strains of humans in Central Africa is an interesting discovery. I expect we’ll ultimately determine it was more than three.