The theory of evolution attempts to explain the staggering diversity of Earth's five million or more living species and answer one of the most basic questions - where did life, and human beings, come from? According to Darwin's theory all living things are related and have descended from a common ancestor - complex creatures evolve from more simplistic ancestors over great periods of time, as genetic mutations occur within an organism's genetic code. If the changes are beneficial and help in survival, the mutations are kept and passed on to future generations. In time, as these mutations accumulate, an entirely different organism appears. Learn more about the forces behind the process, the history of the theory and some of the controversies surrounding it in this book.