The supine position of postnatal human infants

In this review, we discuss the implications of placing an infant in the supine position with respect to human cognitive development and evolution. When human infants are born, they are relatively large and immature in terms of postural and locomotor ability as compared with their closest relatives, the great apes. Hence, human mothers seemingly adopt a novel pattern of caring for their large and heavy infants, i.e., placing their infants in the supine position; this promotes face-to-face communication with their infants. Moreover, infants in the supine position can interact with other nearby individuals in the same manner from an early age. In addition, the infants can also explore their own body parts and/or objects with their hands since the hands are not required to support the body and are therefore, free to move. These activities are considered to be fundamental to the early development of human social and nonsocial cognition, including knowledge of self, in the first six months after birth. Further, developmental continuity in the voluntary exploratory movements in the prenatal period (in utero) to the early postnatal period is also discussed.