Attachment and Health
John Bowlby and Mary Ainsworth developed attachment theory in the 1960s while investigating the effects of maternal separation on infant development. The development of the Strange Situation task in 1965 by Ainsworth and Wittig allowed researchers to systematically investigate the attachment system operating between children and their parents. The Strange Situation involves separating infant-parent dyads and observing infant behaviours upon reunion. Infant behaviour tended to follow patterns, leading to the development of three attachment categories: Secure, Anxious-Avoidant, and Anxious-Resistant. In 1990, Ainsworth added a new category, championed by Mary Main, called Disorganized/Disoriented attachment, characterized by its less reliable pattern of behaviour.
Attachment theory
In his 1951 monograph for the World Health Organization, "Maternal Care and Mental Health", Bowlby put forward the hypothesis that "the infant and young child should experience a warm, intimate, and continuous relationship with his mother in which both find satisfaction and enjoyment", the lack of which may have significant and irreversible mental health consequences. This was also published as "Child Care and the Growth of Love" for public consumption. The central proposition was influential but highly controversial. At the time there was limited empirical data and no comprehensive theory to account for such a conclusion. Nevertheless, Bowlby's theory sparked considerable interest in the nature of early relationships, giving a strong impetus to, (in the words of Mary Ainsworth), a "great body of research" in an extremely difficult, complex area. Bowlby's work (and Robertson's films) caused a virtual revolution in hospital visiting by parents, hospital provision for children's play, educational and social needs and the use of residential nurseries. Over time, orphanages were abandoned in favour of foster care or family-style homes in most developed countries.
Following the publication of "Maternal Care and Mental Health", Bowlby sought new understanding from the fields of evolutionary biology, ethology, developmental psychology, cognitive science and control systems theory. He formulated the innovative proposition that mechanisms underlying an infant's emotional tie to the caregiver(s) emerged as a result of evolutionary pressure. He set out to develop a theory of motivation and behaviour control built on science rather than Freud's psychic energy model. Bowlby argued that with attachment theory he had made good the "deficiencies of the data and the lack of theory to link alleged cause and effect" of "Maternal Care and Mental Health".