The existence of complex life is one of the great mysteries of evolution, for complexity is neither inevitable nor necessary. Indeed, as Mark Ridley shows in this important and thought-provoking book, two major biological hurdles had to be overcome to allow living complexity to evolve. Complex life is constructed from more genes than simple life. But as gene numbers increase, so too do the number of copying errors - it is easier to make a mistake copying the Bible than copying an advertising slogan. Similarly, natural selection encourages gene selfishness, and genes could easily evolve to subvert complex life forms. In retracing the history of life on our planet - from the initial wobbly replicating molecules, through microbes, worms and flies and ultimately to humans - Ridley reveals how life has evolved as a series of steps to deal with error and coerce genes to co-operate within each body. Mendel's Demon offers startling novel perspectives on matters as disparate as the origins of sex and gender, potential cures for AIDS, corporate mergers and acquisitions, and the long-term perils of human cloning.