Imagine life without animals, trees, and fungi. The world would look very different. But while the first life was surely single-celled, we don’t know just how it evolved to multicellular organisms. Two long-term experiments hope to find out, and one has been running for more than 35 years. Hear about the moment scientists watched evolution take off in the lab, and how directed evolution was used to create a multicellular organism. Also, how single embryonic cells become humans, and what all of this says about the possibility of life on other worlds.