What do monkeys tell us about attachment?

Updated: May 3, 2021

Attachment is a form of bond that creates a desire for physical closeness, security and often affection from one being to another (Custance, 2010). Humans often form a strong attachment to their primary caregiver by 7 months old and disruption to that bond can cause distress. In the same way, physical proximity and trustworthy attachment (often referred to as a secure base) can cause confidence and security between a child and their primary caregiver. This essay will evaluate the usefulness of researching attachment in non-human animals, explicitly discussing the research of Harry Harlow (1958) and Mary Ainsworth (1971,1978) cited in Custance (2010, p193-221), and will weigh up how the cost-benefit analysis between research on animals and the value of the research in better understanding attachment.

Non-human animal studies can be useful for conducting research on attachment that would be unethical with humans. Harry Harlow (1958), cited in Custance (2010, p193-221), researched attachment by placing newborn monkeys in a cage with a model mother either covered in terry cloth or made of wire mesh. In the two conditions, milk was provided from one of the model caregivers. Harlow found that when the newborn monkey was placed in a new setting without the terry-cloth mother, it would not have the security and confidence to explore the surroundings and would curl up in a ball on the floor (Custance, 2010). This shows that a secure attachment, based on needs of comfort from the terry-cloth mother, is needed for infants to explore new environments. This research on animals is useful for understanding attachment because it would not be ethically permitted to separate and neglect human newborn’s in the same way. One could argue that the cost-benefit analysis of Harlow’s deprivation and neglect studies on eight monkeys weighs in favour of Harlow as although the baby monkeys suffered greatly, Harlow’s findings ‘in terms of improving our understanding of attachment were profound’ (Custance, 2010, p.211). It should be noted, however, that since Harlow’s research, the British Psychological Society continues to update ethical guidelines to prevent harm in animals when it is unjust. In today’s society, Harlow’s research would not have been permitted so one could argue that the unethical treatment of the animals did not outweigh the value of his findings. Therefore, researching attachment through animals is useful because it provides possibilities for understanding infant-parent bonding that wouldn’t otherwise be possible without non-human participants, although opinions differ as to how much harm an animal should be subjected to in the hope of improving psychological understanding of humans.

Additionally, researching attachment with non-human animals can be useful because ‘they are thought to provide a simpler model of behaviour than that found in human beings’ (Custance, 2010). This makes research easier, quicker and often cheaper to conduct. Humans have brains upto three times the size of other primates so human behaviour is often more sophisticated and complex (Custance, 2010). Harlow’s (1958) monkeys were easier to observe as their behaviour was less complex and easier to control than humans. This can complicate research and cause greater needs to control confounding variables, such as human anthropological differences producing different models of upbringing. Monkeys raise their young on a more intuitive level and are less influenced by knowledge and evaluation of different parenting methods. Harlow's findings were incredibly influential in changing the attitudes of parenting in the Western world from being limited to providing the physical needs of a child, to recognising the value of maternal love and affection in child development (Custance, 2010). Therefore, researching attachment through non-human animals can be very useful for ensuring internal validity because the participant behaviour is simpler and the variables can be easily controlled in a cheaper, quicker and simpler way.

On the other hand, researching attachment with non-human participants isn’t useful because it doesn’t always tell us new things about attachment. Ainsworth (1971,1978), cited in Custance (2010, p193-221), researched attachment with the Strange Situation, a laboratory experiment of observing attachment security involving an infant being present with a primary caregiver, stranger or by themselves to see how the infants behaviour in an unknown setting would differ. Ainsworth concluded very similar results to those of Harlow and found that human caregivers acted as a safe base for children to leave and return to (Custance, 2010). Like Harlow, Ainsworth was able to dispute previous claims that too much affection was damaging to the child’s development, such as those claims of Sigmund Freud and John B. Watson. While conducting her research in Uganda, Ainsowrth concluded the ‘more responsive Ugandan mothers were to their babies’ signals, the less the babies cried and the more confident and explorative they seemed to be’ (Custance, 2010, p.216). Children with a secure attachment base would explore their surroundings in the presence of their mother, in the knowledge they had a safe base to return to if needed. Therefore, research with non-human participants is less useful because it doesn’t tell us new things about secure and insecure attachment in humans.

Overall, researching attachment with non-human animals can be useful in better understanding human attachment when carrying out the research on humans would be unethical. However, valuable research, such as that of Harry Harlow (1958), would no longer be permitted due to ethics and other researchers, such as Mary Ainsworth (1971,1978), have found similar if not the same results as Harlow when conducting more ethical research on humans. Contrastingly, Harlow’s research was influential in changing detrimental Western views of parenting and was one of the first pieces of evidence to argue that a strong attachment between child and caregiver improved the child’s development. His research is also far more internally valid than that of Ainsworth, because the experimental conditions of monkeys are easier to control than those of humans. In conclusion, research on attachment using non-human participants was initially useful as results about the importance of attachment were almost unprecedented. However, today it is less useful as more recent, ethical research with humans provides the same results.


Custance, D. (2010) ‘Determined to love?’, in Brace, N. and Byford, J. (eds) Investigating Psychology, Oxford, Oxford University Press/Milton Keynes, The Open University, pp. 193-221.

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