The story of a quest to uncover the evolutionary history of consciousness from one of the world's leading theoretical psychologists. We feel, therefore we are. Conscious sensations ground our sense of self. They are crucial to our idea of ourselves as psychic beings: present, existent, and mattering. But is it only humans who feel this way? Do other animals? Will future machines? Weaving together intellectual adventure and cutting-edge science, Nicholas Humphrey describes in Sentience his quest for answers: from his discovery of blindsight in monkeys and his pioneering work on social intelligence to breakthroughs in the philosophy of mind. The goal is to solve the hard problem: to explain the wondrous, eerie fact of "phenomenal consciousness"--the redness of a poppy, the sweetness of honey, the pain of a bee sting. What does this magical dimension of experience amount to? What is it for? And why has it evolved? Humphrey presents here his new solution. He proposes that phenomenal consciousness, far from being primitive, is a relatively late and sophisticated evolutionary development. The implications for the existence of sentience in nonhuman animals are startling and provocative.