Marga Vicedo examines scientific views about children s emotional needs and mother love from World War II until the 1970s, paying particular attention to John Bowlby s ethological theory of attachment behavior. Vicedo tracks the development of Bowlby s work as well as the interdisciplinary research that he used to support his theory, including Konrad Lorenz s studies of imprinting in geese, Harry Harlow s experiments with monkeys, and Mary Ainsworth s observations of children and mothers in Uganda and the United States. Vicedo s historical analysis reveals that important psychoanalysts and animal researchers opposed the project of turning emotions into biological instincts. Despite those substantial criticisms, she argues that attachment theory was paramount in turning mother love into a biological need. This shift introduced a new justification for the prescriptive role of biology in human affairs and had profound-and negative-consequences for mothers and for the valuation of mother love.