Northern europeans used to be horrendously violent, absolute savages that had no problems going on bonkers mad sprees of rape, pillage and murder. Over centuries however the practice of weeding out the most violent coupled with severe selective pressures that greatly favored the upper classes resulted in the mellowed out european peoples we see today.
What you describe as "culture" are just the moral selective pressures of any given society at any particular time and whatever idiosyncratic trappings come with it, all of which were selected for.
It's all just evolution running its course.