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Empathy, familial love, anger, social disgust, friendship, minimal decency, gratitude, vengefulness, romantic love, honor shame, guilt, loyalty, humility, awe, judgmentalism, gossip, self-consciousness, embarrassment, tribalism, and righteous indignation: These are all familiar features of human nature, and all socially competent humans have a working understanding of what they are and what they do. . . . All of this psychological machinery is perfectly designed to promote cooperation among otherwise selfish individuals . . . There’s currently no way to prove that all of this psychological machinery evolved, either biologically or culturally, to promote cooperation, but if it didn’t, it’s a hell of a coincidence.
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Joshua D. Greene (Moral Tribes: Emotion, Reason, and the Gap Between Us and Them)