Comments on Thelen and Ulrich's monograph in this issue. Examines theoretical and empirical sections and findings, concluding that the authors have taken a major step forward by introducing the dynamic systems perspective to the study of behavioral coordination in infants, thus opening the way for experimental investigation of phenomena that could…

Maintains that the "getting into shape" hypothesis of explaining the inverted-U distribution of exercise play across age is likely incorrect. Argues that the biological study of human physical activity play, as recommended by Pellegrini and Smith (1998), will reveal whether physical activity play represents an example of…

In all of his published work, Jean Piaget never abandoned his original theoretical framework for the understanding of human development. This framework insists that intelligence is essentially a biological phenomenon; its development is best understood as the development of a sophisticated and highly successful adaptation device. This device…