Towards the end of Tinbergen's scientific career he became increasingly interested in human ethology. At this time he was approached by S.J. and C Hutt, then working at the Park Hospital for Children in Oxford, who asked for his help in their attempts to understand the serious mental disorder, early childhood autism. Tinbergen and his wife, who was very much an active partner and indeed initiator in this work, felt from their long experience of observing animal and human behaviour that autism 'was a deviation from normal behavior development that was quite clearly an exaggeration of normal, anxious, apprehensive "social avoidance behavior", which is such an easily recognizable (and very useful) component of normal childhood behavior'. Dewsbury, D.A. (ed) Leaders in the study of animal behavior, p.457. On his retirement in 1974 the Tinbergens collaborated on a decade long study of autism which, by the application of ethological methods to child behaviour, led to a new theory of its nature and ontogeny and ultimately to a therapy which they championed through a wide range of lectures, publications and personal contacts.