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Whilst Bowlby's early writings on maternal deprivation may be seen as part of the background to the later development of attachment theory, there are many significant differences between the two. At the time of the 1951 publication, there was little research in this area and no comprehensive theory on the development of early relationships. Aside from its central proposition of the importance of an early, continuous and sensitive relationship, the monograph concentrates mostly on social policy. For his subsequent development of attachment theory, Bowlby drew on concepts from ethology, cybernetics, information processing, developmental psychology and psychoanalysis. The first early formal statements of attachment theory were presented in three papers in 1958, 1959 and 1960. His major work "Attachment" was published in three volumes between 1969 and 1980. Attachment theory revolutionised thinking on the nature of early attachments and extensive research continues to be undertaken.