Developmental psychology
Attachment theory, originally developed by John Bowlby, focuses on the importance of open, intimate, emotionally meaningful relationships. Attachment is described as a biological system or powerful survival impulse that evolved to ensure the survival of the infant. A child who is threatened or stressed will move toward caregivers who create a sense of physical, emotional and psychological safety for the individual. Attachment feeds on body contact and familiarity. Later Mary Ainsworth developed the Strange Situation protocol and the concept of the secure base.
Attachment disorder
Attachment theory is primarily an evolutionary and ethological theory. In relation to infants, it primarily consists of "proximity seeking" to an "attachment figure" in the face of threat, for the purpose of survival. Although an attachment is a "tie," it is not synonymous with love and affection, despite their often going together and a healthy attachment is considered to be an important foundation of all subsequent relationships. Infants become attached to adults who are sensitive and responsive in social interactions with the infant, and who remain as consistent caregivers for some time. Parental responses lead to the development of patterns of attachment which in turn lead to 'internal working models' which will guide the individual's feelings, thoughts and expectations in later relationships.