This text addresses one of the most controversial topics in human biology: the role of genes in governing behaviour. Clark and Grunstein act as guides to the current scientific understanding, explaining the genetic and molecular basis of human behaviour within the broader context of animal behaviour generally. They develop the subject clearly, building up from the classic twin studies in humans, and from the most basic behaviours such as chemotaxis in paramecia, to corresponding tropisms and memory in roundworms, and memory and learning in fruit flies, then to complex behaviours of mice and humans. They cover all the politically sensitive issues of behaviour genetics as applied to humans - susceptibilities to disease, eating disorders, aggression, addiction and compulsive behaviours, intelligence, sexual orientation. The authors show why they feel that substantial parts of our personalities and identities are established by our exact genetic complements, without reducing us to powerless creations of our genes.