Personal Genetics Education Project

In the news: Ancient African genome tells complex story of human genetic history

The first genome sequence of an ancient human from Africa was published earlier this month in the journal Science, shedding light on our species’s complex history of migration and genetic mixing. (“First ancient African genome reveals vast Eurasian migration,” Nature)

In recent years, improvements in DNA sequencing technology have made it possible to recover genomic information from the remains of ancient humans, including those from Europe, Asia and the Americas. However, the hot and humid conditions of Africa have made it difficult for such ancient DNA to be preserved. The genome analyzed in this study belonged to a male from around 4,500 years ago, who seems to have been ceremonially buried in a cave in the Ethiopian highlands.

The genome shows that the man, whom the researchers named Bayira (“first born” in the local Gamo language), is most closely related to present day Ethiopian highlanders. The more surprising finding is that, unlike the genome of today’s Africans, Bayira’s genome does not contain DNA inherited from Eurasians (the peoples of Europe and Asia).

Plenty of evidence supports the idea that modern humans migrated out of Africa around 60,000-100,000 years ago and went on to settle all corners of the world. However, recent analyses of DNA from present-day Africans revealed that between 5% (in southern Africa) to 20% (in Ethiopia) of their DNA can be traced back to populations in Europe and Asia. This had led scientists to suggest that there was a reverse migration of people from the Middle East back into Africa around 3,000 years ago. The lack of Eurasian DNA in the newly sequenced genome of Bayira, who lived more than a millennium prior to the purported back-migration, backs up this claim.

Taken together, these studies paint a more complex picture of human population genetics then we may initially appreciate. It shows that the genetic makeup of even those populations or ethnic groups that are considered “isolated” may have been significantly affected by “genetic admixture,” or the mixing of DNA as a result of migrating and interacting populations.

Update: A mistake made by the researchers in the analysis of the data means that part of the study’s conclusion no longer holds up. Go here to read more!

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