Argues that developmental psychologists need attitudes, methods, and conceptual schemes that integrate the distinctive contributions of both nature and nurture in order to study change and consistency in developmental functions, as well as individual differences in behaviors of interest. A conceptual scheme for early mental development is…

Reports a series of studies conducted to investigate possible differences in the exploratory manipulation and play behavior of human infants 7-1/2- 11-1/2 months of age as a function of the attributes of the stimulus, the familiarity of the subject with the stimuli, the age and sex of the infants, and individual differences. (Author/CS)