In order to develop from an embryo, animals as different as fruit flies and humans call on a nearly identical set of genes. But how does this one common genetic toolkit create so many different species? It turns out that it's not the genes you have—it's how you use them. Podcast produced by David Levin. Original interviews by John Rubin. NOVA is produced by WGBH in Boston. Funding for NOVA is provided by ExxonMobil, David H. Koch, the Howard Hughes Medical Institute, the Corporation for Public Broadcasting, and public television viewers. To learn more, go to pbs.org/nova/evolution