The human neonatal stage encompasses the first 28 days after birth. The neonate must quickly adjust her own metabolism to the extra-uterine environment, and this involves temperature regulation, breathing, sleeping, eating, digestion, elimination, and other autoregulatory processes. Even with these adjustments, the human neonate is altricial, that is, born in an undeveloped state and requiring care and feeding by the parents. Anthropologists characterize human neonate altriciality as due to having a large body relative to other apes, a small brain size relative to the human adult, and a prolonged time of extreme motor immaturity relative to other ape neonates. These three traits are an unusual combination for a primate newborn. This combination makes the human infant a costly creature to carry around, protect, and feed —burdens usually falling on the mother. Occasionally other members of the family, even fathers, provide care to the neonate.
Despite being altricial and requiring much care, the neonate is born with several motor and cognitive skills. Most body movements are characterized by automatic inborn behaviors (reflexes) and gross motor activity. All senses are operational. Reflexes orient neonate’s attention toward sound and light. Neonates show a preference for visually following human faces more than other objects. Visual acuity is best at about 19 cm, about the distance between the neonate and mother’s faces when nursing. The neonate has a preference for sweet taste, such as the sugars in breast milk, and is able to distinguish the odor of her mother’s breast milk. The end of the neonatal stage at 28 days coincides with the full nutritional maturity of mother’s breast milk. [Barry Bogin]