Ethological studies of attachment behavior indicate an instinctive need for companionship in animals which is independent of feeding. If the critical period to form attachment to an object passes unused, a fear and flight (avoidance) reaction sets in. Infants need a certain (not as yet quantified) amount of human contact aside from the satisfaction of their physical needs. Deficiency in this contact with mother or mother substitute around the age of six months may lead to marasmus and death. The infant's capacity to elicit and utilize maternal care plays an important role. Similarities and differences between animal attachment behavior and human object relationships are discussed.