Anthropologist Peter Frost has written a couple of interesting articles proposing a process of genetic pacification of the populations in the Roman Empire with its Pax Romana and Medieval Europe.
Frost's argument is that the Roman State the government with courts and constabulary shaped a new version of human who was peaceful and law abiding and worked hard.
This is a similar argument to that made by Gregory Clark, an economist at UC Davis. Clark posted an essay several years ago titledGenetically Capitalist? in which he proposed that the stable social environment and institutions of Medieval England selected for a new kind of human who was less prone to violence, had an affinity for work, had low time preference, and was individualistic in several ways.
States seek to pacify their territories by monopolizing the use of violence. With each passing generation, violent individuals are ostracized, imprisoned, or executed, their predispositions being thereby selected out of the gene pool. Has this “genetic pacification” made longtime State societies kinder and gentler places to live in? Frost Genetic Pacification in Medieval Europe