In a series of twenty chapters, Ernst Mayr presents a consecutive story, beginning with a description of evolutionary biology and ending with a discussion of man as a biological species. Calling attention to unsolved problems, and relating the evolutionary subject matter to appropriate material from other fields, such as physiology, genetics, and biochemistry, the author integrates and interprets existing data. Believing that an unequivocal stand is more likely to produce constructive criticism than evasion of an issue, he does not hesitate to choose that interpretation of a controversial matter which to him seems most consistent with the emerging picture of the evolutionary process.