An axiom of medicine is to diagnose and treat a disease in its formative stages before it becomes so advanced that treatment is difficult or impossible. The same theme runs through aspects of neonatology and developmental pediatrics—organ systems and processes are laid down early in development and supportive or deleterious factors operating during these early stages can permanently influence or alter the course of development.
Belief in "formative Stages was applied to behavior by Sigmund Freud who emphasized the crucial contribution of early experiences to adult personality. A half century later, the same general principle was used to justify Head Start, an educational program that was supposed to equalize the social classes by providing an intellectual boost to disadvantaged children during their formative years.
The principle of "formative years" pervaded theory and practice in developmental psychology for decades, but there were always dissonant findings. For example, five decades of research shows quite clearly that test scores obtained within the first year or two of life do not predict later intelligence for normal children.1 Weight and especially skinfold thickness assessed during infancy do not predict later weight or obesity, and early social disadvantage and stress do not necessarily lead to later psychosocial dysfunction. Indeed, today the emphasis in some quarters of developmental psychology is on change, modifiability, and unpredictability in development rather than on consistency.2