Animal Studies of Attachment

Harlow

Harlow’s research into the importance of love and attachment was initially controversial because behaviourist explanations of attachment were dominant at the time. Behaviourists argued that infants become attached to caregivers because they provide food. Harlow wanted to investigate how newborn rhesus monkeys form attachments to their mothers.

Infant monkeys are highly dependent on their mothers for nutrition, protection, comfort and socialisation. Harlow proposed that attachment develops because mothers provide contact comfort (tactile comfort), suggesting that infants have an innate need for physical comfort and security, rather than simply forming attachments through feeding.

Harry Harlow conducted a number of studies on attachment in rhesus monkeys during the 1950s. His findings challenged learning theory explanations of attachment and highlighted the importance of emotional security in attachment formation.

Wire and Cloth Mother Experiment

Procedure

Harlow (1958) separated eight infant rhesus monkeys from their biological mothers shortly after birth.

The independent variable was the type of surrogate mother available. Each monkey was placed in a cage containing two surrogate mothers:

  • A wire-mesh mother
  • A soft cloth-covered mother

In some conditions, the wire mother provided milk, while in others the cloth mother provided milk.

Harlow wanted to investigate which surrogate mother the infant monkeys would form an attachment to.

The dependent variables included:

  • The amount of time spent with each surrogate mother
  • The monkeys’ behaviour when frightened
  • Their willingness to explore unfamiliar environments

Harlow also carried out fear conditions in which frightening or unfamiliar objects were placed in the cage. In addition, he investigated the long-term effects of early attachment experiences by observing the monkeys’ later social and maternal behaviour.

harlow-machine

Results

The monkeys spent significantly more time with the cloth mother than the wire mother, regardless of which mother provided milk.

The infants only approached the wire mother when feeding and returned to the cloth mother immediately afterwards.

When a frightening object was introduced into the cage, the monkeys ran to the cloth mother for comfort. Once comforted, they were more willing to explore their surroundings. This suggested that the cloth mother served as a safe base from which the monkeys could explore the environment.

Harlow also found important long-term effects. When the monkeys were later introduced to other monkeys, many showed abnormal social behaviour. They were often aggressive, socially withdrawn or unable to interact normally with their peers.

As adults, some of the monkeys experienced difficulty mating. Females that became mothers often displayed poor maternal behaviour and, in some cases, neglected or attacked their offspring.

Conclusions

Harlow concluded that contact comfort is more important than feeding in the formation of attachment bonds.

His findings challenged learning theory explanations of attachment, which suggested that attachment develops simply because caregivers provide food.

The research demonstrated that emotional comfort and security are crucial factors in attachment formation and healthy development.

Isolation Experiments:

harlow 3

Procedure

Harlow also investigated the effects of social and maternal deprivation by rearing infant monkeys in complete isolation.

The monkeys had no contact with other monkeys for varying lengths of time:

  • 3 months
  • 6 months
  • 9 months
  • 12 months

After the isolation period, the monkeys were introduced to other monkeys and their behaviour was observed.

Results

The isolated monkeys displayed a range of abnormal behaviours, including:

  • Rocking backwards and forwards repeatedly
  • Clutching their own bodies
  • Self-directed behaviours suggesting distress

When they were introduced to other monkeys, they initially appeared fearful and often became aggressive.

Many struggled to communicate and interact socially.

They were frequently rejected or bullied by other monkeys because they lacked normal social skills.

Some monkeys also engaged in self-destructive behaviours such as pulling out their hair, scratching themselves and biting their own bodies.

Monkeys isolated for three months generally showed some recovery once returned to a social group. However, monkeys isolated for longer periods, particularly twelve months, often suffered severe and long-lasting social and emotional difficulties.

Conclusions

Harlow concluded that there appears to be a critical period for the formation of attachments and normal social development in rhesus monkeys.

He suggested that monkeys deprived of attachment and social interaction beyond approximately 90 days were much more likely to experience permanent social and emotional difficulties.

His findings demonstrated the importance of early attachment relationships for healthy development.

Additional Findings

Harlow conducted many variations of these studies. His wider programme of research consistently demonstrated that monkeys deprived of maternal care and social contact experienced severe emotional, behavioural and social problems.

Overall, Harlow’s research showed that attachment is not simply based on feeding. Instead, infants have a strong need for contact comfort, security and emotional support from a caregiver. These findings provided important support for attachment-based explanations of development and highlighted the potentially damaging effects of severe early deprivation.

If you would like to learn more about Harlow, I recommend that you watch the documentary below. It gives a fascinating insight to Harlow’s life outside of his research, but also allures to his darker experiments.

Lorenz:

Canada-goose-egg
Lorenz

Konrad Lorenz (1935) investigated imprinting, a form of attachment observed in some bird species, particularly those that are mobile shortly after hatching. Imprinting occurs when a young animal forms an attachment to the first large moving object it encounters after birth. Lorenz believed this process was innate and helped ensure the young animal remained close to its caregiver, increasing its chances of survival.

Lorenz’s research provided evidence that attachment is not learned through feeding, but may instead have a biological basis. His findings later influenced Bowlby’s evolutionary explanation of attachment.

Procedure

Lorenz took a large clutch of greylag goose eggs and divided them into two groups.

  • Half of the eggs hatched naturally with the mother goose.
  • The other half were placed in an incubator.

Lorenz ensured that he was the first moving object seen by the incubator-hatched goslings after they emerged from their eggs. The mother goose was the first thing that the goslings saw when they hatched.

After hatching, Lorenz marked the goslings so he could distinguish between those raised by the goose and those that had imprinted on him.

Later, he placed all of the goslings together under an upturned box. When the box was removed, he observed which individual the goslings chose to follow.

Results

The goslings that hatched with the mother goose followed her wherever she went. The goslings that hatched in the incubator followed Lorenz everywhere he went!

When the two groups were mixed together and released from the box:

  • The naturally hatched goslings followed the mother goose.
  • The incubator-hatched goslings followed Lorenz.

Lorenz concluded that imprinting had taken place. He also observed that some of the geese later displayed sexual imprinting, meaning they directed courtship behaviour towards the species on which they had imprinted during infancy.

Conclusions

Lorenz concluded that attachment behaviour in some species is innate rather than learned. He argued that imprinting occurs during a critical period shortly after hatching. If imprinting does not occur during this period, attachment may not develop normally. His findings suggest that attachment serves an adaptive function by keeping the young animal close to a caregiver for protection and survival.

Important Note for AQA Students

Many textbooks state that imprinting is permanent and irreversible. However, more recent research suggests imprinting may be less rigid than Lorenz originally proposed, with some evidence that later experiences can modify early preferences. Therefore, it is best to say that Lorenz believed imprinting was irreversible, rather than stating it as an established fact.

Key Terms

  • Imprinting: An innate process in which a young animal forms an attachment to the first large moving object it sees after birth.
  • Critical Period: A limited period shortly after birth or hatching during which imprinting is most likely to occur.
  • Sexual Imprinting: The tendency to prefer mates that resemble the object on which an animal imprinted during infancy.
  • Adaptive: A behaviour that increases an organism’s chances of survival and reproduction.

Evaluation:

  • Strength: Support for the role of innate factors in attachment: A strength of Lorenz’s research is that it provides support for the view that attachment has an innate, biological basis. Lorenz found that goslings formed an attachment to the first large moving object they encountered shortly after hatching, even when this was a human rather than their biological mother. This suggests that attachment behaviours can occur automatically without learning or feeding. The implication is that attachment may be adaptive and genetically programmed, supporting Bowlby’s evolutionary theory that infants are biologically predisposed to form attachments because doing so promotes survival.
  • Strength: Influential contribution to attachment theory: A further strength is that Lorenz’s findings had an important influence on later theories of human attachment. His work demonstrated that early attachment experiences may occur during a critical period and highlighted the importance of innate mechanisms in bonding. Bowlby drew on these ideas when developing his monotropic theory of attachment. This is a strength because Lorenz’s research helped shape one of the most influential explanations of attachment in psychology, increasing the theoretical value of his findings.
  • Limitation: Imprinting may not be completely irreversible: Another limitation is that later research suggests imprinting may not be as permanent as Lorenz originally proposed. For example, research by Guiton found that chicks imprinted on a yellow rubber glove later developed a preference for mating with members of their own species after spending time with them. This suggests that early attachments can be modified by later experiences. Therefore, Lorenz may have overstated the permanence of imprinting, reducing the validity of his conclusions about the irreversible nature of early attachment.
  • Point: One limitation of animal studies of attachment is their limited generalisability to humans. Evidence: For example, Konrad Lorenz used geese, whose imprinting behaviour is biologically fixed and differs substantially from human attachment, while Harlow studied rhesus monkeys. Explain: This research lacks generalisability because human attachment is far more complex, involving higher-order cognitive processes and social influences. Consequence: Consequently, this reduces the external validity of animal research, as findings cannot be directly applied to human relationships. Challenge: However, the use of primates in Harlow’s research strengthens the argument for generalisation, as rhesus monkeys share greater genetic and behavioural similarities with humans, particularly as monkeys also form strong emotional bonds. Therefore, his findings may provide a more valid insight into human attachment than studies using less comparable species such as Lorenz.
  • A limitation of Harlow’s study is that the cloth and wire mothers differed in more ways than simply contact comfort. The cloth mother was softer and more closely resembled a real monkey, whereas the wire mother was artificial and less mother-like. This means that factors other than contact comfort may have influenced the monkeys’ preference for the cloth surrogate. As a result, the study lacks internal validity because it is difficult to conclude that contact comfort alone caused attachment.
  • A strength of animal studies is that researchers can exercise a high degree of control over extraneous variables. For example, Harlow manipulated the type of surrogate mother available to the infant monkeys whilst carefully observing attachment behaviour. This enabled him to establish a clear causal relationship between contact comfort and attachment. As a result, the research has high internal validity and provides convincing evidence against learning theory explanations of attachment. However, such tightly controlled laboratory conditions may reduce ecological validity because attachment in real life is influenced by many social and environmental factors that cannot be replicated in a laboratory setting.