Looking at natural peace through Niko Tinbergen's lens

In March 2013, 53 scientists from three continents and a range of disciplines, including anthropology, ethology, evolutionary biology, neuroscience, political science and psychology, attended a week-long workshop at the Lorentz Center of Leiden University entitled 'Obstacles and Catalysts of Peaceful Behavior' (Figure 1). The meeting followed in the footsteps of a symposium and roundtable at the XXV International Ethological Conference in Vienna in 1997 on post-conflict behaviour (de Waal, 2000) that inspired the edited volume 'Natural conflict resolution' (Aureli & de Waal, 2000). The Leiden meeting expanded the concept of natural conflict resolution into a concept of natural peace. Peace is seen here as behavioural process and includes, but is not limited to, mutually beneficial cooperation, helping, sharing, and limiting aggression and restoring tolerance in its aftermath. How and why did these peaceful behaviours evolve and persist? What is their function and how do they develop? Following up on the discussions in Leiden we invited 14 participants at the Leiden meeting and 17 other experts in the field to offer some answers to these questions by means of a contribution to this special issue. While each article stands on its own in terms of its particular contribution to the field, the articles complement each other by offering views from different disciplines within the framework of Tinbergen's four questions.