WORLD OF LEARNING: PLAY

"Recess: Fish, reptiles and some invertebrates appear to play. But when is it play, and not something else? And why do animals do it?" TheScientist 10-1-10

Stuart Brown's Play got into the science and evolution of play, if somewhat breezily (and playfully). This article does so in a more substantial manner, and it's easy to read, and has a cute animal video, besides.