All living plants and animals, including man, are the modified descendants of one or a few simple living things. A hundred years ago Darwin and Wallace in their theory of natural selection, or the survival of the fittest, explained how evolution could have happened in terms of processes known to take place today. In this book John Maynard Smith describes how their theory has been confirmed, but at the same time transformed, by recent research, and in particular by the discovery of the laws of inheritance. This reissue reprints the third edition of John Maynard Smith's classic account, adding a substantial new introduction covering recent developments. A new foreword, by the author of The Selfish Gene and The Blind Watchmaker, commends the book to a fresh generation of readers.