Damasio views brain development through the lens of biological evolution -- starting with the simplest organisms that exhibit elaborate life regulation devices but do not require brains. The arrival of neurons, in some ways no different from other body cells, but also possessed of the unique ability to transmit and receive messages, allows neurons to organize themselves in complex circuits and networks, networks that serve to represent events occurring in the body, influence the function of other cells, even their own function. In this framework, the distinction between body and brain is blurred -- the neurons that make up the brain and eventually generate the mind are body cells and are perpetually connected to the body. Neurons are the producers of mind states. And in the increasing complexity of the patterns in which neurons organize themselves is to be found at once the mystery and the clues to the myriad ways in which the brain operates, manages life and controls human behavior in ways that we are only beginning to understand.

The systems of neurons that govern life in the interior of a body - the process of homeostasis - are first assisted by reflex-like dispositions, and eventually by images, the basic ingredient of minds. But the flexibility and creativity of the human mind do not emerge from images alone. They require images to create a protagonist, a self capable of reflection. Once self comes to mind, the devices of reward and punishment, drives and motivations, and emotions, which have been present all along in at earlier evolutionary stages, can be controlled by an autobiographical self, capable of personal reflection and deliberation. The reflective self becomes a rebellious apprentice to nature's indifferent sorcerer. It uses expanded memory, language, and reasoning to create the very possibility of culture.

This book is a pioneering synthesis of the author's original work over 30 years that attempts to explain how we became fully human--a work that, like Julian Jaynes' The Origin of Consciousness in the Breakdown of the Bicameral Mind, will be read for generations.