Temperament was not a factor in a now famous study performed by Harlow, an animal learning theorist. He was inspired by studies that showed that infants raised in orphanages without handling or loving attention withered away, and often died (Spitz, 1946). Harlow designed an experiment with infant rhesus monkeys, whom he took away from their mother shortly after birth, and raised with two different surrogate mothers instead. One 'mother' was made of bale-wire mesh, the other was covered with terry cloth. Each mother could be equipped with a feeding nipple. Even when the bale-wire mother was the only one providing food, the infant monkeys became more attached to the terry cloth mother and used her as a secure base to explore their environments. This experiment seriously challenged the view of social learning theorists and psychoanalysts who viewed attachment mainly as a function of feeding. Contact and comfort appeared to be most important in the development of attachment, not feeding (Harlow & Zimmerman, 1959).