Play has been difficult to define because it is an aspect of many activities rather than of just a specific kind of activity. Classic theorists such as Piaget and Vygotsky emphasized representational play as play in its purist form, but both immediate and ultimate functions of play can be discerned in simple physical activity play. (Author)

Considers areas of consensus from commentaries, including the value of an evolutionary perspective and the utility of exploring variations in physical activity play. Examines areas of debate, including the nonplay-play distinction, functions of rough-and-tumble play, and the opportunities of juveniles for exercise training. Calls for more directed…

Posits that an evolutionary perspective can unite the study of the typical development for and individual variation within a species and that environments within the normal range for a species are required for species-normal development. Individual differences in children reared in normal environments arise primarily from genetic variation and…