Baby monkeys chose comfort over food when given the choice between two fake mothers

Harry Harlow raised infant rhesus monkeys with two artificial mothers: a bare wire frame that dispensed milk, and a soft cloth-covered frame that dispensed nothing. The infants fed briefly at the wire mother but spent nearly all their time clinging to the cloth one, especially when frightened. The experiment overturned the era's assumption that infant attachment was mainly about feeding, showing that contact comfort mattered more.

— Harry F. Harlow, The Nature of Love — American Psychologist, 1958