“There can be no doubt that our innate moral emotions and instincts were acquired in the hundreds of thousand years—probably half a million years—in which Homo sapiens lived in small hunting and gathering groups and developed a physiological constitution which governed his innate instincts. These instincts are still very strong in us. Yet civilization developed by our gradually learning cultural rules which were trans­mitted by teaching and which served largely to restrain and suppress some of those natural instincts.”