In such prototribal societies, individuals who found it…

““In such prototribal societies, individuals who found it harder to play along, to restrain their antisocial impulses, and to conform to the most important collective norms would not have been anyone’s top choice when it came time to choose partners for hunting, foraging, or mating. In particular, people who were violent would have been shunned, punished, or in extreme cases killed. This process has been described as “self-domestication.”71 The ancestors of dogs, cats, and pigs got less aggressive as they were domesticated and shaped for partnership with human beings. Only the friendliest ones approached human settlements in the first place; they volunteered to become the ancestors of today’s pets and farm animals. In a similar way, early humans domesticated themselves when they began to select friends and partners based on their ability to live within the tribe’s moral matrix. In fact, our brains, bodies, and behavior show many of the same signs of domestication that are found in our domestic animals: smaller teeth, smaller body, reduced aggression, and greater playfulness, carried on even into adulthood.72 The reason is that domestication generally takes traits that disappear at the end of childhood and keeps them turned on for life. Domesticated animals (including humans) are more childlike, sociable, and gentle than their wild ancestors. These””

— Jonathan Haidt