This book frames our biological and psychological capacity to make friends as an evolved ability, comparing friendship to other evolved traits of human beings such as walking upright on two legs, having opposable thumbs and a prominent chin, and possessing the capacity for speech and complex abstract reasoning. Professor John Terrell investigates how the human brain has evolved to perform two functions essential to friendship that, at first glance, appear to be at odds with one another: remaking the outside world to suit our collective needs, and escaping into our own inner thoughts and imagining how things might and ought to be. We must all deal with our species' hereditary legacy-that we are social animals who need to include others in our lives for our biological and psychological survival. Yet we are also able to exercise the cognitive freedom to detach from the adaptive realities and demands of life. These thought patterns have important consequences for how we understand aggression and cooperation. Terrell claims that conflict is best understood in terms of friendship-as challenges that emerge when we are forced to reconcile the inner, private worlds of our imaginations with the experienced realities of our daily lives and each other.