Attachment in Nonhuman Primates

The existence of a mother-infant attachment relationship has been recognized

for many years. For most of those years, however, psychologists explained

the development of this attachment by way of traditional learning

theory. That is, behaviorists argued that the infant-mother attachment develops

because mothers are associated with the powerful, reinforcing event

of being fed. In this way, the mother becomes a conditioned reinforcer. This

reinforcement theory of attachment, however, came into question as a result

of the work of Harry and Margaret Harlow in the early 1960’s.

The Harlows’ work was not with human infants but with infant rhesus

monkeys. They removed newborn monkeys from their mothers at birth and

raised them in the laboratory with two types of artificial or surrogate mothers.

One surrogate mother was made of terrycloth and could provide “contact

comfort.” The other surrogate mother was made of wire. A feeding bottle

was attached to one of the substitute mothers for each of the monkeys.

Half of the monkeys were fed by the wire mother; the other half were fed by

the cloth mother. This allowed the Harlows to compare the importance of

feeding to the importance of contact comfort for the monkeys.

In order to elicit attachment behaviors, the Harlows introduced some

frightening event, such as a strange toy, into the cages of the young monkeys.

They expected that if feeding were the key to attachment, then the

frightened monkeys should have run to the surrogate mother that fed them.

This was not the case, however: All the young monkeys ran to their cloth

mothers and clung to them, even if they were not fed by them. Only the

cloth mothers were able to provide security for the frightened monkeys. The

Harlows concluded that a simple reinforcement explanation of attachment

was inaccurate and that the contact comfort, not the food, provided by a

mother plays a critical role in the development of attachment.

This research provided the impetus for the development of Bowlby’s

ethological account of attachment. Since that time, research by Mary

Ainsworth and Alan Sroufe, as well as many others, has provided important

information for the continuing development of understanding of the complex

relationship between caregivers and infants.