Introduction to the Special Section on The Effects of Early Experience on Development

One cardinal principle in developmental psychology is that early experience has a profound effect upon human development. Infants, once viewed as passive recipients of stimulation, are now understood to be active participants in the physical and social world that surrounds them. Learning takes place from a very early age and sets the course for trajectories of either adaptive or maladaptive behavior. A corollary to this principle is that there are certain periods during early development when experiences have a more significant effect than others. These periods, called sensitive or critical periods, are thought of as windows of opportunity during which certain types of experience have a foundational effect upon the development of skills or competencies. This special section of Child Development takes advantage of major advances in neuroscience, genetics, and improved developmental and statistical methods for studying the effects of early experience to provide readers with a broad range of review and empirical studies on this general topic. The special section is divided into seven parts: the first comprises two invited articles (Fox, Levitt, & Nelson, 2010; Meaney, 2010) that lay out important advances in neuroscience and molecular genetics. The second part provides five articles on fetal development and early experience. The third part contains three articles on perinatal experiences including low birth weight and long-term consequences on health and development, while the fourth part contains four articles on the effects of severe psychosocial deprivation, neglect, and abuse. The fifth part provides the reader with two articles on early experience and stress reactivity, while the sixth part presents three empirical articles examining basic mechanisms linking early experiences including poverty and adoption to behavior. Finally, Jack Shonkoff provides a commentary on the section with an eye toward thinking about the policy implications of the science. The importance of early experience and the identification of sensitive or critical periods have a long history within developmental research. Much of the early work was on the effects of early handling and stress reactivity by developmental psychobiologists such as Seymour Levine (Levine, 1957) and Victor Denenberg (Denenberg, 1964). Their work, primarily in the rodent, illustrated the effects of early handling on later learning and reactivity. The notion of critical periods was introduced to developmental psychology by ethologists, such as Hess and Lorenz (e.g., Hess, 1964) with work on imprinting. Thinking about the effects of early experience on development has been solidified with advances in neuroscience that have described the pattern of brain development during the early months and years of life and the role that experience has in shaping development. Two areas of research have changed the way we conceptualize the effects of early experience and the influences of biology and nurture. The first is the work in neuroscience, done almost exclusively in rodents and nonhuman primates, on the effects of early experience on brain development. The second area is the revolution in our thinking about the role of experience in the action of genes and molecular genetics. Neuroscience has provided an important foundation for our thinking about the role of early experience. Two lines of investigation are notable here. First, the descriptive work of Huttenlocher (Huttenlocher & Dabholkar, 1997) and Rakic (Granger, Tekaia, Le Sourd, Rakic, & Bourgeois,