Individual Differences and Personality, Fourth Edition provides a comprehensive overview of research regarding what personality is and how and why it differs between people. This book begins with a description of the study of personality and then presents basic principles of personality measurement, the concept of personality traits, and the major dimensions of personality variation. Further chapters review personality change and stability, biological causal mechanisms, genetic and environmental influences, and evolutionary adaptive function. Personality disorders are examined as are life outcomes (such as relationships, work, and health) that are predicted by personality characteristics. In addition, the book examines important individual differences beyond personality, such as mental abilities, religious beliefs, political attitudes, and sexuality. Revisions to the fourth edition include updates to all chapters and substantial new content. For example, the developmental change chapter includes new studies of long-term stability, and the biological bases chapter includes new research about the effects of dopamine-like substances on impulse control. The genetics chapter has been heavily revised to cover recent meta-analyses and large-scale studies of the heritability of personality traits. In the chapter on the evolutionary function of personality, the discussion of sex differences is expanded to include cross-cultural variation. The chapter on personality and life outcomes includes new coverage of rating the personality of one's hypothetical ideal partner. The chapter on mental ability has updates on brain volume and IQ and on motivation and IQ.