The possibility that infants' and young children's immature behaviors and cognitions are sometimes adaptive is explored and interpreted in terms of evolutionary theory. It is argued that developmental immaturity had an adaptive role in evolution and continues to have an adaptive role in human development. The role of developmental retardation in human evolution is discussed, followed by an examination of the relation between humans' extended childhood and brain plasticity. Behavioral neoteny, as exemplified by play, is examined, as are some potentially adaptive aspects of infants' perception and cognition that limit the amount of information they can process. Aspects of immature cognition during early childhood that may have some contemporaneous adaptive value are also discussed. It is proposed that viewing immaturity as sometimes adaptive to the developing child alters how children and their development are viewed.Nature wants children to be children before they are men. If we deliberately depart from this order, we shall get premature fruits which are neither ripe nor well flavored and which soon decay. We shall have youthful sages and grown up children. Childhood has ways of seeing, thinking, and feeling, peculiar to itself; nothing can be more foolish than to substitute our ways for them.-Jean Jacques RousseauPeople understandably tend to see development as being progressive: from immature and inefficient structures and functions to mature and efficient ones. Early, immature forms are seen as "unfinished" and incomplete versions of the adult; the child is a "work in progress." From this viewpoint, immaturity is a necessary evil, something that people must get through on their way to adulthood, where the "real show of humanity emerges on stage" (L. Thomas, 1993, p. 175). This is not an unreasonable view. A prolonged period of youth is necessary for humans. Humans, more than any other species, must survive by their wits; human communities are more complex and diverse than those of any other species, and this requires that they have not only a flexible intelligence to learn the conventions of their societies but also a long time to learn them. But the species's physical and cognitive development need not progress synchronously. Their prolonged bodily development could in theory be accompanied by rapid cognitive and social development. This would result in a physically dependent child who has the intellectual and social wherewithal to master the ways of the world.Portions of this article were presented at