DNA from a 2,300-year-old skeleton suggests that the earliest known group of modern humans to branch off from the wider genetic population survived until astonishingly recently. The finding supports the case that southern, rather than eastern, Africa is humanity's ancestral home.
Mitochondrial DNA, passed on only from the mother, demonstrates that all humanity is descended from a single ancestor around 200,000 years ago. Archaeological evidence points to the Omo Valley, where fossil evidence suggests that Homo sapiens roamed Africa 195,000 years ago.
However, over the intervening time a number of populations who also descended from “Mitochondrial Eve” became genetically separated from the rest of humanity. Human genetic diversity in Africa is far greater than elsewhere and is particularly high among the indigenous people of the Kalahari and its surrounding areas, leading to the theory that it is from this region that the great modern human migration began.
The theory also predicts that south-western Africa is the most likely place to find evidence of now extinct groups of people that separated genetically from the wider human family tree, particularly those whose separation occurred quite early.
So when a 2,300-year-old skeleton was found at St. Helena Bay, Professor Andrew Smith of the University of Cape Town was keen to explore the individual's genetics. Smith enlisted Professor Vanessa Hayes of the Garvan Institute, who succeeded in extracting DNA from a tooth and rib.
The man was 1.5 meters tall, consistent with the short stature of many of the distinct populations of the area, and an estimated 50 years old. His right inner ear has bony growths that develop with extensive time in cold water, and shells of the same age near his gravesite provide further evidence that marine foraging provided much of his diet.
The timing of the man's life was significant. “Migration into the region took place around 2,000 years ago when pastoralists made their way down the coast from Angola,” says Hayes. How long the population from which this man came survived the new arrivals is unknown, but it is possible he was one of the last of his tribe.
Despite the acidic soils in which the skeleton lay, the DNA proved highly revealing. Hayes found support for the idea of southern African genetic diversity, and therefore origins. In Genome Biology and Evolution, Hayes and Smith report that complete mitochondrial DNA from the man indicates he was most closely related to the Ju-speaking !Xun population who live to the north of where the man was found.
Nevertheless, Hayes says, “We could demonstrate that our marine hunter-gatherer carried a different maternal lineage to these early migrants—containing a DNA variant that we have never seen before.” It is possible that this divergence was one of the earliest from the common genetics that make up most humans today. As such, Hayes says, it could “Contribute significantly to refining the human reference genome.”