David Reich on migration, mixed ancestries, and ancient DNA

David Reich, professor of genetics at Harvard Medical School and of human evolutionary biology in Harvard’s Faculty of Arts and Sciences, explains how ancient DNA is rewriting what we thought we knew about human history. Drawing on more than 50,000 ancient and modern genomes his lab has studied, Reich shows that the people living in a place today are almost never the direct descendants of the people who lived there before — migration, mixture, and population turnover — are the rule across human history, not the exception. Reich argues that sweeping population mixtures — phenomena we typically associate with the last 500 years (as in the Americas) have deep parallels across Europe, South Asia, and Africa, uncovering connections between peoples that history and archaeology alone could never have revealed.