Pre-natal development of a hypothalamic biological clock.

The available evidence indicates that a biological clock oscillates in the mammalian fetus and that the fetal clock is entrained by redundant circadian signals from the mother. An entrainable biological clock during fetal life helps the developing mammal more readily prepare for life in the outside world. In humans, the early establishment of maternal-infant synchrony may help the infant maximize its responsiveness to the outside world.