Why do amoebas build stalks from their own bodies, sacrificing themselves in the process, so that some may climb up and be carried away from dearth to plenty on the legs of an innocent insect or the wings of a felicitous wind? Why do vampire bats share blood, mouth to mouth, at the end of a night of prey with members of the colony who were less successful in the hunt? Why do sentry gazelles jump up and down when a lion is spotted, putting themselves precariously between the herd and hungry hunter? And what do all of these have to do with morality in humans: Is there, in fact, a natural origin
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