the brief time of my employment by the World Health Organization there was no possibility of developing a new one". He then went on to describe the subsequent development of attachment theory. Because he was dissatisfied with traditional theories, Bowlby sought new understanding from such fields as evolutionary biology, ethology, developmental psychology, cognitive science and control systems theory and drew upon them to formulate the innovative proposition that the mechanisms underlying an infant's tie emerged as a result of evolutionary pressure. "Bowlby realised that he had to develop a new theory of motivation and behaviour control, built on up-to-date science rather than the outdated psychic energy model espoused by Freud." Bowlby expressed himself as having made good the "deficiencies of the data and the lack of theory to link alleged cause and effect" in Maternal Care and Mental Health in his later work Attachment and Loss published in 1969. Ethology and evolutionary concepts From the 1950s, Bowlby was in contact with leading European ethologists, namely Niko Tinbergen, Konrad Lorenz, and Robert Hinde. Bowlby was inspired by the study Lorenz conducted on goslings, showing that they imprint on the first animate object they see. Bowlby was encouraged by an evolutionary biologist, Julian Huxley, to look further into ethology to help further his research in psychoanalysis as he introduced Bowlby to the impactful work by Tinbergen on "The Study of Instinct". Bowlby followed this guidance and became interested in ethology as he wanted to rewrite psychoanalysis in order to focus this research field around a concrete theory in which psychoanalysis was lacking. He admired the methodological approach to ethology that psychoanalysis was not familiar with (Van der Horst, 2011). From reading widely in ethology, Bowlby was able to learn that ethologists supported the theoretical ideas through concrete empirical data. Using the viewpoints of this emerging science and reading extensively in the ethology literature, Bowlby developed new explanatory hypotheses for what is now known as human attachment behaviour. In particular, on the basis of ethological evidence he was able to reject the dominant Cupboard Love theory of attachment prevailing in psychoanalysis and learning theory of the 1940s and 1950s. He also introduced the concepts of environmentally stable or labile human behaviour allowing for the revolutionary combination of the idea of a species-specific genetic bias to become attached and the concept of individual differences in attachment security as environmentally labile strategies for adaptation to