DNA Discoveries in Central Africa

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.

6 comments… add one
  • TarsTarkas Link

    To my knowledge no known hominid fossils earlier than Homo erectus have been discovered outside of Africa, whereas any number of hominid species have been found in Africa, including H. erectus. Human genetic diversity in sub-Saharan Africa is notably higher than elsewhere in the world. All of the great apes except for orangutans live in Africa. How old is ‘modern’ H. sapiens? Depends on the paleantologist.

    Species, subspecies, and varieties are a constantly shifting panoply of definitions, I see this all the time in botany. IMO Homo is like Canis; coyotes, jackals, and wolves seem to be clearly defined species, yet they can successfully hybridize with each other. Thus modern humans were able to mate with Neandertals and Denisovans and incorporate their genes into their own genome.

  • TarsTarkas Link

    Some even argue that Australopithecus is really part of the Homo continuum. Where is a Tardis when we need one?

  • bob sykes Link

    The studied were pygmies.

    The comparison to canids is apt. Based on DNA and earlier blood testing, it seems pretty clear that there are 50 to 100 different human races now extant. An honest taxonomist would sort them into 10 or 20 different species. The big split is between Eurasians and everyone else.

  • Actually, the greatest separation is between Australian Aboriginals and everybody else. There is more genetic diversity in sub-Saharan Africa than in the whole rest of the world put together.

    We are not multiple species. We are not even multiple subspecies. A better analogy is to the different breeds of dogs. They are all the same species and subspecies.

    The example of dogs actually underscores my point about the longevity of the human species. At this point we distinguish between Homo sapiens and other members of genus Homo based on morphology. Morphology is a lousy way of identifying species. Who would actually place St. Bernards and Italian greyhounds in the same species based on morphology alone?

    The better question is whether Canis familiaris and Canis lupus are one species or two.

  • TarsTarkas Link

    Bob: In the early days of paleantology every hominid discovered in Europe was named a new species based on morphology. This was due to each site was effectively a genetic isolate due to terrain and other factors. When the number of species reached double digits the system broke down. We see this all the time in modern zoology and botany. In the Pacific northwest there were a number of species of Impatiens defined by morphology, habitat, and flower color. When the orange jewelweed invaded the region they all began hybridizing with it and now many of these ‘species’ are effectively extinct. The same thing happened with the hundreds of colorful cichlid fish species in the East African lakes, isolated by habitat and breeding habits. Once sedimentation from overcultivation of surrounding land turned the water murky, they began hybridizing.

    Dave: There is some discussion whether dogs are descended from a now extinct species of wolf that was hunted or bred out of existence. Horses and Cattle are two other species which are extinct in the wild (Tarpans and Aurochs). The jungle fowl from which our chicken came from has become critically endangered due to backcrossing with domesticated strains, in fact the best and purest remaining population of the species may live in the Deep South of the USA. You may find this article interesting.


  • Grey Shambler Link

    250,000 years. Less than 17,000 human generations. We have a fair history of the last 5,000 years, or about 333 generations in which we have seen little or no morphological change. 17,000/333=51, lets say, evolutionary time blocks, for random, beneficial mutations to occur and flourish throughout the human population. I’m not buying it. There’s some sleight of hand here. It’s too much for the blind monkey at the typewriter. We can assume the same 5,000 years for dogs, with ten times as many generations, extreme morphology change, but no speciation.

Leave a Comment