Athenian vs. Spartan, Imperialist vs. Republican, Roundhead vs. Cavalier, monarchist vs. revolutionary, Bolshevik vs. Menshevik, Christian Democrat vs. Social Democrat, capitalist vs. socialist, fundamentalist vs. progressive, Labor vs. Tory, Democrat vs. Republican. For the 12,000 years that humans have lived in mass-scale societies, they have clashed?often violently?over the proper way to design, structure, and maintain those societies. The persistence and intensity of political conflict seems surprising in light of people’s oft expressed longing for consensus, unity, and peace. Our complaints about polarization and partisanship, and our conviction that we should all be able to agree on our collective best interests, are belied by the combative actions of many. Yet this search for common ground is often fruitless. The fights may vary across battlefield, bureaucracy, and ballot box, but political conflict remains an inevitable constant in human society. The purpose of this book is to explain why. Predisposed presents evidence that people differ politically not just because they grew up in different cultures or were presented with different information. All these factors certainly play their role but people also differ politically because they have diverse psychological, physiological and genetic traits. This biologically-based, physio-cognitive machinery influences much of what makes people who they are, including their personalities, preferences for occupation and leisure pursuits, tastes in art and music, strategies for child rearing and, yes, orientations to politics. In short, this machinery predisposes people to see and understand the world in different ways. These predispositions are in turn responsible for a significant portion of the political conflict that marks human history. It is a remarkable story?a story suggesting that buried in many people and operating largely outside the realm of conscious thought are forces inclining them toward particular political convictions. It is also a story that can engender tolerance. Political disputes typically spring from the assumption that those who do not agree with us are shallow, misguided, uninformed, and ignorant. Our story suggests instead that political opponents simply experience, process, and respond to the world differently. It follows, then, that the key to getting along politically is not the ability of one side to persuade the other side to see the error of its ways but rather the ability of each side to see that the other side is different, not just politically, but physically. Predisposed will change the way you think about politics and partisan conflict.