Completely revised and updated, Peter Gray's best-selling psychology text gives a new emphasis to the importance of evolutionary concepts. Psychology is introduced by describing the main theories, and the evidence supporting them, in a coherent and stimulating way. Gray encourages students to think about behaviour and the 'whys' and 'hows' by exploring its functions, purposes and biological mechanisms. All the main psychology questions are identified, and the different approaches to answering them, are assessed.