Home Science 4500-Year-Old Ethiopian DNA Rewriting Human Prehistory

4500-Year-Old Ethiopian DNA Rewriting Human Prehistory

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Extremely rare Ethiopian DNA from a man who lived there about 4,500 years ago is leading researchers to reconsider ancient human migrations throughout Africa.

The conventional wisdom for some time has been that the first modern humans evolved in Africa, then migrated from Africa around 70,000 years ago, first pit-stopping in the Middle East before moving to Europe, Asia and the rest of the globe. However, it also appears that around 3,000 years ago, a group of farmers from the Middle East and Turkey returned to the Horn of Africa with crops like wheat, barley and lentils.

This current understanding of early human migrations has been pulled together by population geneticists by comparing the DNA of various groups of people alive today. However, since humans originally came from Africa, DNA from an ancient African unmixed with the returning Eurasian genes has long been sought as it would offer a valuable genetic baseline for researchers to trace changes in the human genome over time.

The details of the study were published this Thursday in the academic journal Science.

More on Ethiopian DNA from “Mota”

The body that the Ethiopian DNA was recovered from was found face-down in Mota cave, in the highlands in the southern part of Ethiopia. The unusual cool and  dry conditions in the cave preserved the DNA in the skeleton, and researchers took a sample from the petrous bone at the base of his skull (sampling the resilient inner ear bone is the method of choice for obtaining DNA in a non-ideal climate). The DNA sequence is they recovered is the first nuclear genome from an ancient African.

Using a method of comparing sections of Mota’s genome with the same sites in individuals from 40 populations in Africa and 81 populations in Europe and Asia, the researchers determined that Mota was most closely related to the Ari, an ethnic group that still lives not far away in the highlands of Ethiopia.

As would be expected, Mota did not possess any of the genetic variants for light-colored eyes or skin that had evolved in the populations that left Africa. Mota also did not have any of the genetic variants that developed in early Eurasian farmers that made it possible for them to digest milk as adults.

Of interest, anthropologists John and Kathryn Arthur of the University of South Florida first discovered the skeleton in 2012 at Mota Cave when local elders led the pair to the cave, which had been used a hiding place during wartime.

Initial radiocarbon testing suggests that the skeleton was close to 4,500 years old. That means that the man behind the skeleton “Mota” clearly lived before Eurasians came back to Africa.

What caused massive migration back to Africa 3000 years ago?

One key result of the study was that scientists could compare Mota’s DNA to that of modern Africans, which made it possible for the researchers to accurately estimate how large the Eurasian influx had been. The results were somewhere between surprising and stunning.

“Roughly speaking, the wave of West Eurasian migration back into the Horn of Africa could have been as much as 30% of the population that already lived there – and that, to me, is mind-blowing. The question is: what got them moving all of a sudden?” Andrea Manica, senior author of the study from the University of Cambridge’s Department of Zoology, commented in a statement following the publication of the study.

Manica and his colleagues report East Africans today can have as much as 25% of their DNA attributed to the Eurasian back flow. Of note, even in the far western and southern areas of Africa, a minimum of 5% of the local human genome is Eurasian.

A key question raised by the new research is, of course, what could have caused such a large migration of early human beings over such a short period of time (a few hundred years). The authors of the paper admit they are scratching their heads as to what could be behind this kind of a massive migration.

Manica et al. point out that they really can’t tell the whole story just on the basis of one new find. However, as the techniques for extracting and analyzing the ancient DNA improve, we are likely to see more studies filling in the gaps in the story of early human migrations.

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