Lorenz had conducted a study on attachment with goose. He had a batch of goose eggs and had separated them into bow groups. One group of eggs would have been naturally hatched by the mother, and the second group would have been hatched by an incubator. Lorenz had then marked the eggs to differentiate between the incubator eggs and the eggs naturally hatched by the mother. Lorenz had discovered that the goslings that were hatched by the mother would follow the mother, where as the goslings that were hatched by the incubator, followed Lorenz around. Lorenz had then explained that then goslings were imprinted onto Lorenz and this imprinting process would happen in the critical period in the first few seconds after the gosling had hatched from the egg. Lorenz had also added that goslings that were imprinted onto humans would then, as adults, attempt to mate with humans. However, this study can be criticised with Guitons study who had concluded that chickens that were imprinted onto rubber gloves would try to mate with the object, as Lorenz had predicted, however with experience, the chickens would shift back to attempting to mate with other chickens. This show that imprinting on mating behaviour was not as permanent as Lorenz had believed. It can also be criticised as there is anthropomorphic bias in the study. This is applying human attributes to animals and believing that what can be learned form animals can be applied to humans and this is a criticism because of the differences between the species of the animals and a humans as humans have different complexities compared to goslings and so it is very difficult to generalise what is learnt from animals to humans.

Harlow had conducted a study on attachment with rhesus monkeys. Harlow had separated the monkeys from their mother and had raised them in cages. In the cages were constructed surrogate mother where one was a wire mother that produced milk, and the other was a soft, cloth mother that did not produce milk. There was also a blanket that was in each of the cages with the monkeys and the monkeys had shown signs of distress whenever the blanket was removed, similar to when a baby is separated from their mother. The amount of time spent with each mother was recorded. The monkeys had shown signs of attachment towards the cloth mother compared to the wire mother and had only gone to the wire mother for food, and in some cases, leaned over to the wire mother for food whilst still holding onto the cloth mother. This shows that monkeys for attachments based on comfort over the provision of food. When Howard had attempted to frighten the monkeys, they would return to the cloth mother for comfort instead of the wire mother, which again shows that the monkeys had formed attachments based on comfort and not the provision of food. However, Harlow’s study can be criticised because there are many ethical issues with the study. The monkeys had suffered greatly from the study. And because the species was deemed similar enough to humans to the point where the results could be generalised to humans, the monkeys suffering was likely to be humans like. Harlow was also aware of the suffering caused, however it can be argued that Harlow’s research was sufficiently important to justify the effects caused.