We tend to think of animals as survival machines, their every action designed to help them avoid threats, fulfill needs, and find mates. But what are we to make of a crow that repeatedly places a discarded plastic lid at the top of a snowy roof and then rides it down the pitch like a snowboard? Or orcas that drape dead salmon across their foreheads — a strange behavior that spreads to neighboring pods before disappearing entirely? What evolutionary purpose could these behaviors possibly serve?  From birds and mammals to reptiles, fish, cephalopods, and even insects, scientists continue to observe behaviors in animals that look for all the world like play. And while exactly how these activities are beneficial isn’t always obvious, researchers increasingly believe they are evolutionarily important. “Play is a really serious business,” says Marc Bekoff , professor emeritus of ecology and evolutionary biology at the University of Colorado Boulder and author of The Emotional Lives of Animals .…