The evolutionary theory states that attachment is formed due to an innate tendancy within everyone which we are born with.
Bowlby said that attachment is something that has evolved through natural selection and has aided humans to survive. Bowlby said that infants make attachments to help them survive and they usually make one main attachment to the primary caregiver which is usually the mother, this is also known as monotropy. He also stated that attachment must take place within the fist two and a half years of a child's life, this is known as the critical period. If this attachment is broken, the child will face maternal deprivation. Bowlby suggested that this meant they would become affectionless psychopaths, he also said that the negative effects of attachment are irreversible.
A study that refutes Bowlby's theory is Schaffer and Emerson on the Glasgow babies, this study showed that more than a third of the babies had multiple attachments, not just with the primary caregiver (the mother) therefore going against Bowlby's idea of monotropy as the study shows that babies have the ability to form close bonds with numerous people rather than just the one.
Another research that refutes the idea of a critical period in Bowlby's theory of evolution is Rutter's study showing how Romanian orphans that were in institutional care and were later adopted by families from USA and UK were able to form attachments with them…