No form of behavior is accompanied by stronger feeling than is attachment behavior. The figures towards whom it is directed are loved and their advent is treated with joy. So long as a child is in the unchallenged presence of a principal attachment-figure, or within easy reach, he feels secure. A threat of loss creates anxiety, and actuall loss, sorrow; both, moreover, are likely to arouse anger. —John Bowlby
Most higher animals have evolved instinctive bonding mechanisms that keep the youngsters close to the parents. Human infants, too, are born with tendencies to form special attachments; all parents know their powerful effects. Early in life, most children become attached to one or a few family members or caretakers, sometimes so firmly that for several years such children may never stray more than a few meters from the attachment-figure. During those years, a prolonged separation of the child from those particular persons may be followed by an enduring depression or disturbance, during which the child's personality does not develop normally.
What is the function of childhood attachment? The simplest explanation is that it evolved to keep children within a safe sphere of nurture and protection. But according to our theory, our human bond machinery has the additional function of forcing children to acquire values, goals, and ideals from particular older individuals. Why is this so important? Because even though there are many ways a child could learn about ordinary causes and effects, there is no way for a child to construct a coherent system of values — except by basing it upon some already existing model. The task of constructing a civilized personality must be far beyond the inventive power of any single individual. Furthermore, if too wide a variety of adult models were available, it would be too hard to build a coherent personality of one's own, because one would have to pick and choose fragments from all those different personalities — and this might lead to so many conflicts and inconsistencies that many of them would cancel each other out. It would simplify the child's task if the attachment mechanism restricted attention to only a few role models.
How did our attachment-bonds evolve? In many species of animals, attachment occurs so swiftly and firmly that scientists who study animal behavior call it imprinting. Presumably, the machinery that makes us learn our parents' goals is descended from the mechanisms of our animal ancestors. Presumably our infantile attachment-bonds form as soon as various inborn systems learn to distinguish the parents' individual peculiarities — first by senses of touch, taste, and smell; then by sound of voice and, finally, by sight of face.
Once those attachment-bonds are formed, a child won't react in the same way to the faces and voices of strangers and parents, for these have different effects on how we learn. The effect of an attachment-person's affection or rejection is not like that of ordinary success-failure goal-rewards — which merely teach us what to do in order to achieve our goals. Attachment-related signals seem to work directly on those goals themselves — and thus can modify our personalities. Attachments teach us ends, not means — and thus impose on us our parents' dreams.