The Cambrian explosion was one of the most spectacular events in the history of life. In a short window of geological time an abundance of new animals—and new animal body designs—arose fully formed without evidence of any evolutionary ancestors.

Charles Darwin viewed this as an inexplicable mystery. He had envisioned the evolution of life through a multitude of small, undirected steps. Yet, the fossil record reveals no such pattern of gradual development. Instead, early in the Cambrian period, compound eyes, articulated limbs, sophisticated sensory organs and skeletons burst into existence seemingly out of nowhere.

Darwin’s Dilemma explores the Cambrian explosion and the scientific controversy that still surrounds it. Where are the missing transitional forms that Darwin’s theory requires? Can any undirected evolutionary process explain the origin of animals?