I Introduction. - Statement of the problems. - The Herring Gull. - The Three-spined Stickleback. - The Grayling. - Types of social co-operation. - II Mating Behaviour. - The functions of mating behaviour. - Some instances of timing. - Persuasion and appeasement. - Orientation. - Reproductive isolation. - Conclusion. - III Family and Group Life. - Family life. - Group behaviour. - IV Fighting. - Reproductive fighting. - The functions of reproductive fighting. - The causes of fighting. - The peckorder. - V Analysis of Social Co-Operation. - Recapitulation. - The actor's behaviour. - The behaviour of the reactor. - Review of releasers. - Conclusion. - VI Relations Between Different Species. - The release of reactions. - The avoidance of release. - VII The Growth of Social Organizations. - Differentiation and integration. - The establishment of social ties. - Further developments. - Conclusion. - Regulation. - VIII Evolutionary Aspects of Social Organization. - The comparative method. - Comparison of social systems. - Comparison of releasers. - Conclusion. - IX Some Hints for Research in Animal Sociology. Language: English