The psychologist Harry Harlow (c. 1958), with one of his experimental rhesus monkeys, used for his studies on maternal love.
In his most famous experiment, he separated infant monkeys from their mothers at birth, and placed them with a pair of surrogate mothers: one wire frame mother, and one cloth mother with a face. In one condition, the wire mother had a milk bottle built into her chest, while in the second condition, the the cloth mother had the milk bottle. In both conditions, the monkey would feed from the milk-possessing mother, but regardless of the food source, the infant spent the majority of its time clutching to the warmer, more life-like cloth mother. Harlow (1958) concluded:
Certainly, man cannot live by milk alone. Love is an emotion that does not need to be bottle- or spoon-fed, and we may be sure that there is nothing to be gained by giving lip service to love
H. F. Harlow (1958). The nature of love. American Psychologist, 13, 673–685.