The Red Queen
The book begins with an evolutionary account of sex itself, defending the theory that sex flourishes, despite its costs, because a mixed heritage confers to each generation a defensive "head start" against parasites and disease. The basic reason for this is the way sexual reproduction increases the genetic variety in a population. This greatly increases the chance of at least some individuals surviving the onslaught of predators, parasites and diseases. This much is common ground amongst evolutionary theorists.