This past fall, a scientist named Steve Hsu made headlines with a provocative announcement. He would start selling a genetic intelligence test to couples doing IVF: a sophisticated prediction tool, built on big data and machine learning, designed to help couples select the best embryo in their batch. We wondered, how does that work? What can the test really say? And do we want to live in a world where certain people can decide how smart their babies will be? This episode was produced by Simon Adler, with help from Rachael Cusick and Pat Walters. Fact-checking by Michelle Harris. Engineering help from Jeremy Bloom. Special thanks to Catherine Bliss. Radiolab’s “G” is supported in part by Science Sandbox, a Simons Foundation initiative dedicated to engaging everyone with the process of science.