INNATE PROGRAMMING.
Bowlby (1969) suggested that attachment could be understood within the framework of evolutionary principles, that all psychological and physical characteristics are naturally selected. A characteristic is selected because it helps those individuals who possess that characteristic to survive and reproduce. It is important to realise that this notion of selection is a passive one - no one is doing the selecting - it is selective pressure. The essential principle is that any inherited behaviour that increases an individual's chances of survival and reproduction will be passed on to the next generation and thus continues to reappear in subsequent generations. It has been selected because of its usefulness.
The result is that infants are born 'programmed' to become attached and adults are also 'programmed' to form this kind of relationship with their infants. Social releasers are necessary to ensure an interaction takes place. These are social behaviours that elicit a caregiving reaction from another, such as smiling, crying, cooing and simply looking appealing. Bowlby suggested that these behaviours are innate in infants (and other non-human animals), and that the responses are innate in caregivers. They are critical in the process of forming attachments.