Harvard geneticist David Reich has spent years extracting DNA from ancient human remains. What the data shows keeps defying every assumption scientists had built. Every population ever studied is profoundly mixed. Britain alone has been almost completely replaced four or five times over. The hunter-gatherers who built Stonehenge's foundations? Gone within a century. The idea of a clean lineage connecting any living person to any ancient place is, as Reich puts it, simply untenable. DAVID REICH:  So if you ask the question, a white British person today, and you say this person feels like they’re pure descendants of people who lived in Britain a long time ago, nothing could be further from the truth. They’re like homeopathic, diluted compared to the hunter-gatherers or the first farmers. And this idea that any one people is somehow purely descended from the people who lived in the past — and it was a common thing that people thought prior to the genetic revolution — is being confronted with this data.…