With so many cooperative tendencies built into human brains, whether by genes or culture or both, why isn’t there more harmony in the world? Unfortunately, notes Boyd, one of humans’ most successful cooperative endeavors is making war. “All that increased cooperation has done is change the scale on which conflict takes place,” he says. “I would like to think there’s a happy story of peace and understanding. But you can’t be a 21st century human and not see that the trend is in the other direction.”

Getchen Vogel, ‘The Evolution of the Golden Rule’, Science, vol. 303, no. 5561 (February 20, 2004), p. 1131