Human beings evolved in a tribal environment. Over the millennia, our brains have become adept at fostering social networks that are the basis of group cohesion, from the primary family unit to the extended associations of clans, villages, cities, and nations. This essential social component of our behavior gave the human species distinct survival advantages in coping with the challenges of an often-hostile environment. This book examines the many ways in which our tribally oriented brains perceive and sometimes distort reality. The author describes how our social nature led to the development of cognitive tricks that have served us so well as a social species. Some examples are our habit of imposing patterns on random phenomena, of weaving entertaining narratives to explain the mysteries of the universe, and of favoring the biases of group think. Luckily, we also stumbled upon science, which McRae views as a fortuitous accident. With this new technique, humans had discovered a method of objectively evaluating the accuracy of our traditional tribal notions. Even more important, the scientific method proved to be self-correcting, allowing us to weed out the bad ideas from those that really work. McRae argues that science is our most successful social enterprise to date. Through the sharing of scientific ideas, our species has expanded the reach of the tribal community to a global scale. Our problems may be bigger than ever, but science gives us a sure basis in reality and the best method of facing the daunting challenges of the future.