Ridley recounts the hundred years' war between the partisans of nature and nurture to explain how this paradoxical creature, the human being, can be simultaneously free-willed and motivated by instinct and culture. With the decoding of the human genome, we now know that genes not only predetermine the broad structure of the brain, they also absorb formative experiences, react to social cues, and even run memory. They are consequences as well as causes of the will.