One of the most interesting case studies done using primates is Harlow’s Surrogate Study. The results revolutionized our understanding of social relationships in early development.
The goal of the experiment was to see if babies were attached to their mothers primarily because the mother was a source of food. Dr. Harry Harlow and other social and cognitive psychologists argued this idea didn’t take into consideration the importance of physical touch and love in promoting healthy development.
Preceding experiments used infant Rhesus monkeys that were taken away from their mothers and raised in a laboratory. Some infants were placed in separate cages away from peers.
While in social isolation, the monkeys showed disturbed behavior, staring blankly, circling their cages, and even engaging in self-mutilation. When the isolated infants were re-introduced to the group, they had trouble interacting. Many avoided the other primates and sadly some even died after refusing to eat.
Interestingly, the infant monkeys who were raised without mothers but with the benefit of a social group still developed social deficits, showing reclusive tendencies and clinging to their cloth diapers.
Harlow speculated the soft material of the diapers simulated the comfort provided by a mother’s touch. This observation led to the now-famous Harlow’s Surrogate Mother experiment.
Harlow took infant monkeys from their biological mothers and substituted two surrogate mothers. One was in the form of simple construction of wire and wood, and the second was covered in foam rubber and soft cloth material.
The experiment had two important variables corresponding with the surrogate mothers. In the first, the mother made with wire had a milk bottle readily available for the infants to drink from while the cloth mother did not. The opposite was true in the second environment.
The experiment revealed the infants spent significantly more time with the cloth mother than the mother made with wire.
When the infants would feed from the mother made of wire, they would immediately return to the soft mother after feeding.
Harlow also observed the infants used the surrogate mothers as form of reassurance. When faced with uncertain situations, they would hide behind the mothers. When the mothers weren’t present, they would be paralyzed with fear.
If a threatening toy was placed in the cage, infants with a surrogate mothers showed more courage by attacking the toy while others without a surrogate mother would hide.
The two studies resulted in groundbreaking empirical evidence for the importance of parent-child attachment relationship involving love and touch.