Source: The New Yorker.
In a book review in "The New Yorker" of Hanno Sauer's new book "The Invention of Good and Evil: A World History of Morality", Nikhil Krishnan writes:
It was five million years ago, Sauer tells us, that creatures rather like ourselves, having only just evolved from some now extinct ape, started to develop the psychological dispositions that made them capable of coöperation. Unlike the chimpanzees and bonobos of the dense forests around central Africa, our ancestors had to survive in exposed grasslands. Coöperating for mutual defense against our predators, and for collectively pursuing prey, was our way of compensating for our new vulnerability. Among the dispositions that emerged to help us get along, Sauer writes, was the capacity for altruistic behavior: “putting aside the interests of the individual in favour of a greater common good.”Source: Nikhil Krishnan.
In short, according to this theory, there was a competitive advantage for our species to cooperate. Today, when we're good, it's because we evolved that way. So, how do we explain wars? Or even closer to home, how do we explain the rancorous divisions in America's body politic?