A few months ago, co-Host Latif Nasser, who was otherwise healthy, saw blood in his poop. It was the start of a medical journey that made him not only question what was going on in his body, but also dig into the secret genetic story of how we became human. Curled up in a hospital bathroom, Latif tries to sort out whether his ordeal is the result of a long-lost sibling knifing him in the gut or, on the contrary, a long-forgotten kindness shared between two human-ish travelers. 

Special thanks to Azra Premiji, Avir Mitra, Suzanne Lehrer, David Reich, Sriram Sankararaman, Ainara Sistiaga, Carl Zimmer, Carly Mensch, Latif's GI Doctor Florence Damilola Odufalu and her entire team, and the staff at LA County-USC Medical Center and Keck USC hospitals who looked after Latif during his hospitalization.

Support Radiolab by becoming a member of The Lab today.    

Radiolab is on YouTube! Catch up with new episodes and hear classics from our archive. Plus, find other cool things we did in the past — like miniseries, music videos, short films and animations, behind-the-scenes features, Radiolab live shows, and more. Take a look, explore and subscribe!