Like many new parents, Priscilla Dunstan was at her wit s end trying to ease the crying of her colicky infant son. Then she made a startling discovery: His sounds varied according to his needs, and she could decipher their meaning by tracking the sound as a physical reflex. Unlike learned languages, Dunstan soon realized, every newborn from birth to three months possesses a natural, reflexive communication system for signaling hunger, tiredness,...