This volume continues the tradition of the Life-Span Development Series, presenting overviews of research programs on a variety of developmental topics. Research and theory in life-span development have given increased attention to the issues of constancy and change in human development and to the opportunities for, and constraints on, plasticity in structure and function across life. Acknowledging the need for and existence of interconnection between age and developmental periods, it focuses on conditions for possibly discontinuous development that emerge at later periods. Contributors to this series are sensitive to the restrictive consequences of studying only specific age periods, such as old age, infancy, or adolescence. Each scholar attempts to relate the facts about one age group to similar facts about other age groups, and to move toward the study of transformation of characteristics and processes over the life span.