How and when the first modern human populations emerged out of Africa to settle Europe and Asia has been at the center of a long-standing debate among researchers and scholars. The results of a new genetic study, however, suggests that modern humans made their first successful major migration out of Africa around 55,000 – 60,000 years ago through Egypt, and not from further south through Ethiopia, as suggested by another proposed theory.
Dr. Luca Pagani, of the Wellcome Trust Sanger Institute and the University of Cambridge in the UK, and his colleagues analyzed the genetic information from six modern Northeast African populations (100 Egyptians, and five Ethiopian populations each represented by 25 people).
“Two geographically plausible routes have been proposed: an exit through the current Egypt and Sinai, which is the northern route, or one through Ethiopia, the Bab el Mandeb strait, and the Arabian Peninsula, which is the southern route,” Dr. Pagani explains. “In our research, we generated the first comprehensive set of unbiased genomic data from Northeast Africans and observed, after controlling for recent migrations, a higher genetic similarity between Egyptians and Eurasians than between Ethiopians and Eurasians.”
It suggests that Egypt was most likely the way out of Africa.
The team also used high-quality genomes to estimate the time that the populations split from one another: people outside Africa split from the Egyptian genomes more recently than from the Ethiopians (55,000 as opposed to 65, 000 years ago), supporting the idea that Egypt was the last stop on the route out of Africa.
“While our results do not address controversies about the timing and possible complexities of the expansion out of Africa, they paint a clear picture in which the main migration out of Africa followed a northern, rather than a southern route,” says Dr Toomas Kivisild, a senior author from the Department of Archaeology and Anthropology, University of Cambridge.
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Human genome sequences from Ethiopians and Egyptians point to a Northern exit out of Africa as the most likely route by the ancestors of all Eurasians. Image courtesy Luca Pagani
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The northern route is also best supported by the known genetic mixture of all non-Africans with Neanderthals, who were present in the Levant at the time, and with the recent discovery of early modern human fossils in Israel (close to the northern route) dating to around 55,000 years ago.
“This important study still leaves questions to answer,” says Dr Chris Tyler-Smith, a senior author from the Wellcome Trust Sanger Institute. “For example, did other migrations also leave Africa around this time, but leave no trace in present-day genomes? To answer this, we need ancient genomes from populations along the possible routes. Similarly, by adding present-day genomes from Oceania, we can discover whether or not there was a separate, perhaps Southern, migration to these regions.”
“Our approach shows how it is possible to use the latest genomic data and tools to answer these intriguing questions of our human origins and migrations,” he added.
In addition to providing insights on the evolutionary past of all Eurasians with their new findings, the researchers have also developed an extensive public catalog of the genomic diversity in Ethiopian and Egyptian populations.
“This information will be of great value as a freely available reference panel for future medical and anthropological studies in these areas,” says Dr. Pagani.
The findings are published in the American Journal of Human Genetics*.
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Portions of this article were adapted and edited from the subject Cell Press and Welcome Trust Sanger Institute press releases.
*American Journal of Human Genetics, Pagani et al.: “Tracing the route of modern humans out of Africa using 225 human genome sequences from Ethiopians and Egyptians” http://dx.doi.org/10.1016/j.ajhg.2015.04.019.
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