In most narratives, the story of evolution is the story of organisms emerging from the ocean and eventually populating the land. But for some species, that evolution also involved a return trip. Dozens of major mammal and reptile groups ultimately made their way back to the beach and into the water. A new Yale study has undertaken the task of explaining when and how this happened—and which species fully re-committed to the life aquatic. The study is published in the journal Current Biology.