Within 20, maybe 40, years, most people in developed countries will stop having sex for the purpose of reproduction. Instead, prospective parents will be told as much as they wish to know about the genetic makeup of dozens of embryos, and they will pick one or two for implantation, gestation, and birth. And it will be safe, lawful, and free. Stanford’s Hank Greely joins science writer Carl Zimmer for a conversation about the revolutionary biological technologies that make this future a seeming inevitability and the deep ethical and legal challenges humanity faces as a result.