Sergio M Pellis, PhD (Monash Univ., Australia) is a biologist and ethologist, presently Professor of Animal Behavior and Neuroscience at the University of Lethbridge, Alberta, Canada. He spent 1982-1990 at the University of Illinois, Tel Aviv University, and University of Florida, where he received post-doctoral training in behavioral neuroscience and movement analysis. A central focus of his research is on the evolution, development and neurobiology of play behavior. Findings from his laboratory on rats has shown that play experiences with peers during the juvenile period leads to changes in the anatomy of the prefrontal cortex which may underlie the improved executive functions that such experience produces. Moreover, it is the rough and tumble, rule following and monitoring of cheating during play interactions that seems to provide the experiences that are promoting the development of these skills.