In this timely collection, biological and behavioural scientists address questions about the origins and interconnections of altruism and aggression that have been emerging from new research, within and across species. They explore the genetic basis of affiliative and aggressive orientations as well as the biological correlates of these behaviours. They consider environmental variables - family patterns, child-rearing practices - that influence prosocial and antisocial behaviours and they examine internal processes such as empathy, socio-inferential abilities and cognitive attributions, that regulate 'kindness' and 'selfishness'. The authors take an ethological perspective, placing special importance on the need to explore altruism and aggression in the real lives and natural habitats of humans and other animals. A wide audience of psychologists and ethologists will find this book a useful resource.