This volume brings together a collection of papers written by contributors to a symposium entitled “Evolution, function, development, causation: Tinbergen's four questions and contemporary animal biology,” held at the Institute of Biology, Leiden University, the Netherlands on 5 September, 2003. The symposium was organized by The Royal Dutch Zoological Society (KNDV) with the Dutch Society for Behavioural Biology (NVG), to commemorate the 40th anniversary of the publication of Niko Tinbergen's seminal paper “On aims and methods of ethology.” Leiden was a fitting venue for the symposium, because Tinbergen held a chair there before he left in 1949 to become a demonstrator in the Department of Zoology at Oxford. Moreover, the symposium was held at the “van der Klaauw laboratory,” and it was Professor Cornelis van der Klaauw who invited Konrad Lorenz to a symposium on “instinct” held in Leiden in November, 1936. That was the first time that Tinbergen and Lorenz met, a meeting that culminated in a life-long friendship. Indeed, Tinbergen's “aims and methods” paper was dedicated to Lorenz on the occasion of his 60th birthday.

In his paper, Tinbergen discussed the field of ethology, now usually known as behavioral biology, and defined it as “the biological study of behaviour.” The “aims and methods” paper is best known for the identification of four major problems in the study of behavior: causation, development (ontogeny), function (survival value), and evolution.