Bowlby argues infants are born with an attachment gene that programmes to exhibit innate behaviours called social releasers which increase their chances of receiving care such as clinging, crying and smiling
Support comes from Lorenz's theory of imprinting. Newborns imprint an image of the first moving object they see within hours of being born. Lorenz's research showed goslings imprinted on Lorenz as he was the first image they saw after hatching. This supports the theory because it shows that attachment is an innate process as the infants were too young to have learned anything at this stage.
Tronick et al provides evidence to support Bowlby's theory. They studied an African tribe where it was tradition for infants to be looked after and even breastfed by different women in the tribe. It was found that despite being fed by different women, at 6 months the infants still showed a primary attachment to their biological mother. This is positive as it suggests that infants will have a monotropic bond with their mother despite interacting with other individuals
Schaffer and Emerson (1964) provide evidence against Bowlby's theory. They found from observing infants in Glasgow that they had made many attachments and often the main attachment was the father. They concluded that attachments could be formed with many different people. This is a problem because monotropy predicts the mother should be the main attachment figure, not the father.
Researchers have criticised the idea of the critical period. Rutter et al (199) found while it may be less likely attachments will form after the critical period, it is not impossible. It was concluded that a more accurate term to describe this period is a sensitive period to reflect the fact although it is an important window of time in which children are most likely to form an attachment, bonds can still be formed outside this window. This is a problem as it suggests Bowlby's theory may be overly negative about the chances of healthy development following early deprivation