Our brains were designed for tribal life, for getting along with a select group of others (Us) and for fighting off everyone else (Them). But modern times have forced the world’s tribes into a shared space, resulting in epic clashes of values along with unprecedented opportunities. As the world shrinks, the moral lines that divide us become more salient and more puzzling. We fight over everything from tax codes to gay marriage to global warming, and we wonder where, if at all, we can find our common ground. A grand synthesis of neuroscience, psychology, and philosophy, Moral Tribes reveals the underlying causes of modern conflict and lights the way forward. Greene compares the human brain to a dual-mode camera, with point-and-shoot automatic settings (“portrait,” “landscape”) as well as a manual mode. Our point-and-shoot settings are our emotions—efficient, automated programs honed by evolution, culture, and personal experience. The brain’s manual mode is its capacity for deliberate reasoning, which makes our thinking flexible. Point-and-shoot emotions make us social animals, turning Me into Us. But they also make us tribal animals, turning Us against Them. Our tribal emotions make us fight—sometimes with bombs, sometimes with words—often with life-and-death stakes.