For people with little or no knowledge of the science of human intelligence, this volume takes readers to a stage where they are able to make judgments for themselves about the key questions of human mental ability. Each chapter addresses a central scientific issue but does so in a way that is lively and completely accessible. Issues discussed include whether there are several different types of intelligence, whether intelligence differences are caused by genes or the environment, t e biological basis of intelligence levels, and whether intelligence declines as we grow older.