Humans live in large and extensive societies and spend much of their time interacting socially.Likewise, most other animals also interact socially.Social behaviour is a source of constant fascination to biologists and psychologists of many disciplines; from behavioural ecology to comparative biology and sociobiology.The two major approaches used to study social behaviour involve either the mechanism of behaviour – where it has come from and how it has evolved – or the function of the behaviour studied.Featuring guest contributions from leaders in the field, this book presents both theoretical foundations and recent advances to give a truly multidiscplinary overview of social behaviour for advanced undergraduate and graduate students.Topics include aggression, communication, group living, sexual behaviour and cooperative breeding.With examples ranging from bacteria to social mammals and humans, a variety of research tools are used, including candidate gene approaches, quantitative genetics, neuroendocrine studies, cost– benefit and phylogenetic analyses, and evolutionary game theory.IntroductionThe uphill climb of sociobiology: towards a new synthesisTamäs Székely, Allen J.Moore and Jan KomdeurSocial behaviour garners broad interest: biologists, social scientists, psychologists and economists all incorporate a consideration of social behaviour in their studies.This breadth of interest is unsurprising, as the vast majority of animals (and all that reproduce sexually) live partly (or fully) in social environments.As Robert Trivers (1985) succinctly put it, 'Everybody has a social life.' Some of this interest undoubtedly emerges because members of our own species (Homo sapiens) live in extensive societies and spend much time interacting with each other.Yet you do not have to be human for social behaviour to have a strong influence on biological processes.The significance of social behaviour is easy to see: if you isolate an ant, a fish or a bird from its peers in a sort of Kaspar Hauser setup, within a short time many of its 'normal' behaviours will change and be impaired.Social behaviour, heuristically defined as activities among members of the same species that have fitness consequences for both the focal individual and other individuals in the group, is thus ubiquitous.The perplexing causes and far-reaching implications of social behaviour make it a rich subject to help understand evolution (Gardner & Foster 2008).The understanding ofsocial evolution is challenging, given that social behaviour is often costly.Furthermore, unlike many traits that are passively selected by the environment, in the context of social behaviour the animals create selection for themselves by interact- ing with each other.This added complexity requires more complex models and clever experiments to dis- entangle cause and effect.Although the study of social behaviour goes back thousands of years (Dugatkin 1997), it is this complexity arising from interactions that fascinates evolutionary biologists.Our enthusiasm for social behaviour led us to discuss the various ways we can study and understand social behaviour among animals.In 2006 the three of us drafted an outline of an ambitious book, and contacted Cambridge University Press with the out- line.Our main motivation was the lack of a compre- hensive volume that would cover both proximate and ultimate aspects of social behaviour, and go beyond taxon-specific treatises on some of the workhorses of social evolution (e.g.social insects, birds and mammals).Social behaviour has come a long way since the pioneering papers of Hamilton (1964) and Maynard Smith and Price (1973), and the landmark syntheses of Wilson (1975) and Trivers (1985).Given the stimulus of these papers and books, researchers investigated social behaviour with renewed vigour.Furthermore, the subsequent decades have applied new tools and new perspectives, and have gained new insights: advances in molecular genetics, neurobiology, mathematical theories of social behaviour and phylogenetic methods fundamentally changed the way we study animal behaviour, and what we know about social traits.We thought that to further advance sociobiology would require a comprehensive book which provides an overview of theoretical foundations and recent advances, and looks at implications beyond evolutionary biology.