How disgust made humans cooperate to build civilisations

The young man was having sex with his dog. In fact, he’d lost his virginity to it. Their relationship was still very good; the dog didn’t seem to mind at all. But the man’s conscience was eating at him. Was he acting immorally? In search of sage counsel, he sent an email to David Pizarro, who teaches a class on moral psychology at Cornell University in New York. ‘I thought he was just pulling my leg,’ said Pizarro. He sent the man a link to an article about bestiality, and thought that would be the end of it. But the man responded with more questions. ‘I realised this kid was pretty serious.’

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