In The Science of Good and Evil (Times Books, 2004), I argued that we evolved moral emotions that operate similarly to other emotions, such as hunger and sexual appetite. Thinking of these emotions as proxies for highly efficient computational programs deepens our understanding of the process.
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Similarly, in making moral choices about whether to be altruistic or selfish, we feel guilt or pride for having done the wrong or right thing. But the moral calculations of what is best for the individual and the social group were made by our Paleolithic ancestors. Emotions such as hunger, lust and pride are stand-ins for such computations.