Bowlby was in some ways, like Freud, a late starter. Although he had a substantial body of related work behind him, it was not until around his fiftieth year, in a series of papers published between 1958 and 1963 (Bowlby, 1958d; 1960d; 1961c), that he began to formulate the main outlines of Attachment Theory. Perhaps psychological theorising, like novel writing, unlike poetry or mathematics, requires a certain maturity; perhaps, like his hero Darwin, Bowlby’s revolutionary spirit was combined with a cautiousness that meant he needed to be absolutely certain of his ground before attempting to challenge the heavens. Bowlby had always felt some unease about the scientific status of psychoanalysis: his discovery of ethology in the 1950s provided him with the scientifically secure base from which to make his conceptual advance: ‘The time is already ripe for a unification of psychoanalytic concepts with those of ethology, and to pursue the rich vein of research which this unification suggests’ (Bowlby, 1953c).