They are only modified if there is some form of selection though, like for example some people say of the Dutch and their height.

In modern times it is more likely that culture and education augments genetics such that your violent tendencies are repressed, you are brought up leading a soft and comfortable life, taught to be polite and kind, etc. Contrast to maybe someone brought up in a warzone or some other place.

I mean post apocalyptic shows like the walking dead express this quite well (at least the first few seasons) where once society falls it's just a free for all and back to our roots again.

Yeah, i'm pretty sure observational studies after natural disasters (those who followed up Katerina especially) showed that it wasn't really the case. Yes, you have looters everywhere (Even in Japan), but most people help their neighbours (or even strangers if those looks non-threatening). Only when you have a central authority figure present and a lot of people you see riot and aggression, hence the reason why in most countries that need help, aid distribution is as decentralized as possible nowadays (centralized distribution is a _really_ good way of having people killed in the mass anyway).