Scholars interested in play in humans should take note of the growing literature on play in other species, especially in light of the application of evolutionary approaches to virtually all areas of psychology. Although most research on animal play deals with mammals--particularly rodents, carnivores, and primates--studies have recorded play of different types in a wide range of other animals, both vertebrate and even invertebrate, who differ greatly in their ecology, their behavior, and their nervous systems. How we characterize such diverse forms of play shapes how we pose research questions and evaluate evidence about play in all species, including humans. In this article, the author reviews the research about play across major taxonomic divisions and looks at the questions that arise when anthropocentric views of play are set aside in order to understand play more broadly. The author then considers how this knowledge illuminates the diversity of play among humans, whom he sees as on the edge of evolutionary change. The article concludes that an understanding of the evolutionary and comparative diversity of play may have implications for integrating play into education and into other attempts to solve ills in society.