In 2010, Ratcliff started working with brewer’s yeast, the single-celled fungus we use to make bread and beer. He repeatedly grew the yeast in liquid-filled tubes, shook them, and then used the cells that sank fastest to start new cultures. By favoring cells that stick together and settle faster, this simple procedure radically changed the yeast within just 60 days. Now whenever a cell divided in two, the new cells didn’t drift apart as they normally would; instead, they remained attached, creating beautiful, branching snowflakes that comprised dozens of cells. The yeast had evolved multicellularity in just two months.