Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past

David Reich's 2018 book presents the revolution in ancient DNA research and what it reveals about human prehistory. Reich, a geneticist at Harvard, shows how DNA extracted from ancient skeletons has overturned long-held assumptions about human migration, population mixing, and the peopling of every continent. The research reveals that nearly all human populations are products of repeated, large-scale migrations and admixture events — not the stable, separate groups conventional history assumed.

Andreessen groups it with Henrich's book as "two more books on who we are and how we got here, one on culture, the other on genetics." The pairing frames both books as first-principles investigations of how the world came to be the way it is.

For a founder, Reich's book is a case study in first-principles thinking applied to history. His field upended its own received wisdom within a decade because new technology (ancient DNA sequencing) made evidence available that had never existed before. The old models of static, isolated populations turned out to be wrong because they were built on the assumption that archaeologists had found everything there was to find. The founder lesson is about epistemology: when a new measurement technology becomes available, it often invalidates the consensus built on the old measurement technology. So many startup opportunities arise from exactly this pattern — a new data source or sensing capability reveals that the "settled science" of an industry was built on assumptions that are now testable and wrong. Reich's story also demonstrates the value of investing in long-shot fundamental research without knowing the commercial application.