> ... ancestrally, if you had no coalition you were nakedly at the mercy of everyone else, so the instinct to belong to a coalition has urgency, preexisting and superseding any policy-driven basis for membership. This is why group beliefs are free to be so weird. Since coalitional programs evolved to promote the self-interest of the coalition’s membership (in dominance, status, legitimacy, resources, moral force, etc.), even coalitions whose organizing ideology originates (ostensibly) to promote human welfare often slide into the most extreme forms of oppression, in complete contradiction to the putative values of the group. Indeed, morally wrong-footing rivals is one point of ideology, and once everyone agrees on something (slavery is wrong) it ceases to be a significant moral issue because it no longer shows local rivals in a bad light. Many argue that there are more slaves in the world today than in the 19th century. Yet because one’s political rivals cannot be delegitimized by being on the wrong side of slavery, few care to be active abolitionists anymore, compared to being, say, speech police. 

> Moreover, to earn membership in a group you must send signals that clearly indicate that you differentially support it, compared to rival groups. Hence, optimal weighting of beliefs and communications in the individual mind will make it feel good to think and express content conforming to and flattering to one’s group’s shared beliefs and to attack and misrepresent rival groups. The more biased away from neutral truth, the better the communication functions to affirm coalitional identity, generating polarization in excess of actual policy disagreements. Communications of practical and functional truths are generally useless as differential signals, because any honest person might say them regardless of coalitional loyalty.