A billion years ago single-celled organisms ruled the Earth. Now multicellular creatures are everywhere, including animals like us. But how did our ancestors go from one cell living alone to many cells working together? In this film we meet five microscopic cousins who take different approaches to a multicellular life. Read more at https://www.nature.com/articles/d41586-025-02635-2 Subscribe to Nature Briefing, an unmissable daily round-up of science news, opinion and analysis free in your inbox every weekday: https://www.nature.com/briefing