In the course of mammalian evolution from lower mammals to primates to our species, childhood became an increasingly larger part of the life span. Although there are powerful advantages of this extended childhood in socialization and the opportunity to try out new behaviors in the comparative safety of play, there is the serious disadvantage of the child’s inability to survive on its own. This helplessness is especially pronounced in human infants, who cannot walk until roughly 1 year of age and who, early in life, must be carried by a parent. Human infants cry when they are uncomfortable, thereby bringing to them the caretaker, almost always the mother. The nurturance of the mother tends to be rewarded by the infant’s responsivity or its smiles. The mother, of course, is strongly motivated to nourish and protect her child. It is only natural, then, that a strong social bond develops between infant and mother, a bond called attachment.