Bioethics Blogs

Out of Africa: DNA Analysis Points to a Single Major Exodus

Credit: NASA

If you go back far enough, the ancestors of all people trace to Africa. That much is clear. We are all Africans. But there’s been considerable room for debate about exactly when and how many times modern humans made their way out of Africa to take up residence in distant locations throughout the world. It’s also unclear what evolutionary or other factors might have driven our human ancestors to set off on such a perilous and uncertain journey (or journeys) in the first place.

By analyzing 787 newly sequenced complete human genomes representing more than 280 diverse and understudied populations, three new studies—two of which received NIH funding—now help to fill in some of those missing pages of our evolutionary history. The genomic evidence suggests that the earliest human inhabitants of Eurasia came from Africa and began to diverge genetically at least 50,000 years ago. While the new studies differ somewhat in their conclusions, the findings also lend support to the notion that our modern human ancestors dispersed out of Africa primarily in a single migratory event. If an earlier and ultimately failed voyage occurred, it left little trace in the genomes of people alive today.

In one of the three studies published in Nature [1], NIH grantee David Reich of Harvard Medical School, Boston, and colleagues report on the genome sequences of 300 people from 142 different populations around the globe. The DNA samples, part of the Simons Genome Diversity Project, were carefully chosen to span much of the variation in human genetics, language, and culture.

The views, opinions and positions expressed by these authors and blogs are theirs and do not necessarily represent that of the Bioethics Research Library and Kennedy Institute of Ethics or Georgetown University.