Attachment theory posits that infants need to form a close relationship with at least one primary caregiver to ensure their survival and to develop healthy social and emotional functioning. It was first developed by psychiatrist and psychoanalyst John Bowlby (1907–90). The theory proposes that secure attachments are formed when caregivers are sensitive and responsive in social interactions, and consistently available, particularly between the ages of six months and two years. As children grow, they are thought to use these attachment figures as a secure base from which to explore the world and to return to for comfort. Interactions with caregivers have been hypothesized to form a specific kind of attachment behavioral system – or, more recently, internal working model – the relative security or insecurity of which influences characteristic patterns of behavior when forming future relationships. Separation anxiety or grief following the loss of an attachment figure was proposed as being a normal and adaptive response for a securely attached infant.
In the 1970s, developmental psychologist Mary Ainsworth expanded on Bowlby's work, codifying the caregiver's side of the attachment process as requiring the adult's availability, appropriate responsiveness, and sensitivity to the infant's signals. She and her team devised a laboratory procedure known as the Strange Situation Procedure, which she used to identify attachment patterns in infant–caregiver pairs: secure, avoidant, anxious attachment, and later, disorganized attachment. In the 1980s, attachment theory was extended to adult relationships and attachment in adults, making it applicable beyond early childhood. Bowlby's theory integrated concepts from evolutionary biology, object relations theory, control systems theory, ethology, and cognitive psychology, and was most fully articulated in his trilogy, Attachment and Loss (1969–82).
