Bowlby proposed that babies are born with a set of innate 'cute' behaviours like smiling, cooing and gripping that encourage attention from adults, which he referred to as social releasers.
Bowlby recognised that attachment is a reciprocal process, with mother and baby having innate predispositions to become attached and social releasers triggering that response in caregivers.
Bowlby proposed that there is a critical period around 2 years when the infant attachment system is active, and if attachment is not formed at this time, a child will find it much harder to form one later.
Bowlby proposed that a child forms a mental representation of their relationship with their primary caregiver, which he referred to as an internal working model.
The internal working model effects the child's later ability to be a parent themselves, with children from functional families tending to have similar families themselves.
Bowlby's theory is not supported by Schaffer and Emerson who found that a significant minority of babies appeared to be able to form multiple attachments at the same time.
When the primary attachment figures were instructed to ignore the babies signal, the babies showed distress or curling up and lying motionless, supporting the theory that cute infant behaviours are intended to initiate social interactions.
Bowlby's theory is also supported by evidence that the internal working model effects the child's later ability to be a parent themselves, with children from functional families tending to have similar families themselves.