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Six human teeth unearthed in East Africa are helping scientists to understand how our ancestors moved around the continent 50,000 years ago.
The remains were discovered in the Magubike rockshelter, in the southern highlands of Tanzania. This site is thought to have been occupied by humans for thousands of years, the sediment in the shelter littered with broken bones and stone tools.
Now, researchers have made a bigger discovery: six human teeth, plus ostrich-shell beads and animal bones, dating back at least 45,000 years.
This is a significant find: while modern humans are thought to have evolved in Africa during the Middle Stone Age (MSA, about 320,000 to 30,000 years ago), finding human remains from that period in this particular region of the continent is incredibly rare.
Tim Compton, a visiting researcher at the Museum, says, 'These six teeth are important because very few others are associated with the Middle Stone Age in this part of East Africa. Not only that, the teeth probably all come from the upper jaw of a single, relatively young individual with only modest tooth wear, which means that features of the crowns are still clear.'
This level of preservation has allowed the scientists to accurately compare the teeth to those from other African and non-African dental remains. The study uncovered potential ancient links between eastern and southern African populations, with the results being published in PLOS ONE.
The teeth found in Magubike show some striking similarities to those of the San people.
Today, the San number roughly 90,000 people spread across Zimbabwe, Angola, South Africa, Namibia and Botswana. Studies that have looked into the DNA of the San suggest they are highly distinctive, having differentiated from other groups perhaps some 100,000 years ago, and remaining largely isolated since.
'Genetic data from present-day African populations suggest that the San people of southern Africa are one of the most distinctive, with deep and separate roots from populations living further north,' says Tim.
Yet the discovery of these teeth in Tanzania may alter this narrative.
While identifying features on the Magubike teeth are not unique to the San, they occur more commonly among this group than other sub-Saharan Africans. This implies that at least 45,000 years ago, people related to modern-day San may have lived over far greater distances than they do today.
This past connection between people in East Africa and the southern African peoples may also be reflected in languages spoken today. The San people speak distinct languages known collectively as Khoisan, which are unrelated to most other African language families, but show some resemblances to those spoken by groups of people still living in northern Tanzania.
Using a scanning electron microscope, the researchers were able to create a high-resolution 3D model of the teeth. This showed the scratches on their surface in fine detail.
Dr Silvia Bello, a researcher studying the evolution of human behaviour at the Museum, says, 'What is interesting - and what I did for the paper - is the analysis of these scratches on the front teeth, which suggest the use of these teeth as a third hand.
'A behaviour seen elsewhere, but which seems to be shared by different species of hominins, including Homo heidelbergensis, Neanderthals and modern humans.'
The scratches are likely the result of holding food, or another material such as hide, between the teeth while cutting it with a stone tool. Occasionally the tools would have cut too deep, caused incisions on the surface of the teeth.
Because of how these scratches were formed on the teeth, they can also be associated with handedness. The direction and orientation of the marks are consistent with other fossils that indicate a right-handed individual, although the researchers note that the heavy erosion on the teeth cannot definitively confirm this.
For a long time, scientists have debated where in Africa our species originated.
But Prof Chris Stringer, a Museum researcher who was also involved in the study of the Magubike teeth, says, 'Homo sapiens probably descended from a set of interlinked groups of people, who were separated and connected across the continent of Africa at different times.
'Each one had different combinations of physical features, with their own mix of ancestral and modern traits. By 50,000 years ago, ancestors of modern populations in Africa were differentiating, and the Magubike teeth show us that the present distribution of people like the San is not necessarily a reliable indicator of where their ancient ancestors lived.'