The power of Darwin's theory of natural selection is beyond doubt, it explains how useful adaptations are preserved over generations. But evolution's biggest mystery eluded Darwin: how those adaptations arise in the first place. Can random mutations over a 3.8 billion years be solely responsible for wings, eyeballs, knees, photosynthesis, and the rest of nature's creative marvels? And by calling these mutations `random', are we not just admitting our own ignorance? What if we could now uncover the wellspring of all biological innovation? Renowned evolutionary biologist Andreas Wagner presents the missing piece in Darwin's theory. Using cutting-edge experimental and computational technologies, he has found that adaptations are in fact driven by a set of laws that allow nature to discover new molecules and mechanisms in a fraction of the time that random variation would take. Consider the Arctic cod, a fish that lives in waters cold enough to turn the internal fluids of most organisms into ice crystals. And yet the Arctic cod survives by producing `natural anti-freeze', proteins that lower the freezing temperature of its body fluids. The invention of those proteins is an archetypal example of nature's enormous powers of creativity. Meticulously researched, carefully argued, and full of fascinating examples from the animal kingdom, Arrival of the Fittest offers up the final puzzle piece in the mystery of life's rich diversity.