Harvard geneticist David Reich has rewritten human prehistory using ancient DNA. In this conversation we go past the headlines — past the Yamnaya, past the Neanderthal admixture story most listeners already know from his book and from his appearances elsewhere — and into the parts that don't usually get airtime: — The ghost populations. Entire civilizations that left no pottery, no tools, no bones we can identify, and yet whose genetic signatures are scattered across every living human. The people who built Stonehenge. The people who crossed Beringia. We know they existed because we are partly them. We will never know what they called themselves. — The 90% replacements. In a handful of centuries — a cosmic blink — populations across Europe and South Asia were almost entirely overwritten. Reich walks through what the genomes actually say versus what the archaeology said for a century. — The methodological argument. Reich treats genomes as thousands of independent genealogical records and distinguishes systematic from statistical error the way a physicist would. We compare ancient DNA's rigor to the standards in cosmology and ask what each field can teach the other. — The 5-million-year black hole. The unresolvable gap in the primate-to-human lineage that no amount of sequencing will currently close, and what Reich would do with one perfect Homo erectus genome if he had it. — Mythology as memory. Flood narratives, founder myths, and what genetic drift in small isolated groups can and cannot tell us about whether ancient stories preserve real events. — Founder effects and the modern clinic. Why arranged marriage and small ancestral populations produce the disease patterns we see in Ashkenazi Jews, Finns, and other groups today — and what that means for medicine. — The cultural cost. Genetics is dismantling national-purity myths in real time. Reich is candid about what it is like to publish findings that contradict the founding stories of entire peoples. This is a different cut of David Reich than you have heard before on Dwarkesh Patel. Less Bronze Age selection, more epistemology — how do we know what we know about a past with no written record, and what should we do when the genome contradicts the textbook. — Get my new book, Focus Like a Nobel Prize Winner. Join my mailing list at briankeating.com to enter the monthly meteorite drawing. Join this channel for monthly office hours and member perks. My books Think Like a Nobel Prize Winner Losing the Nobel Prize Dialogue Concerning the Two Chief World Systems — the first-ever Galileo audiobook Subscribe for long-form conversations with the people shaping how we understand reality. No dumbing down. #universe #podcast #briankeating #intotheimpossible #science #astronomy #cosmology #cosmicmicrowavebackground #intotheimpossible #briankeating #davidreich #dwarkeshpatel