"If I did not exist, nothing would exist, because there would be nothing to which oppose oneself", writes Fernando Pessoa in the devil's name. Is this the invention of a poet? Nothing is less sure. The scientist confirms the notion that life is born from the confrontation between molecules. J.D. Vincent invites us here to explore with him all the aspects, the ramifications, from animal life to the human brain, which are nurtured by this principle of opposition. The devil is constantly at work in the heart of the living, and neurobiologist Jean-Didier Vincent demonstrates this evidence with humor in his book, a continuation of the spirit present in his Biology of Passions.