Since Charles Darwin wrote about “evolutionary fitness,” the idea of fitness has been confused with physical strength, tactical brilliance, and aggression. In fact, what made us evolutionarily fit was a remarkable kind of friendliness, a virtuosic ability to coordinate and communicate with others that allowed us to achieve the all the cultural and technical marvels in human history. But this gift for friendliness came at a cost. Survival of the Friendliest offers us a new way to look at our cultural as well as cognitive evolution and sends a clear message: in order to survive and even to flourish, we need to expand our definition of who belongs.