I'm inclined to doubt whether it's correct to assume that the kind of things that we are likely to include under "violence" are mainly a hangover from a primitive more violent world.

Generally speaking the evidence seems to indicate that hunter gatherers lead relatively un-violent lives, especially as regards other hunter gatherers, but even when it comes to killing for food, in the sense that this often tends to be associated with rituals of respect and apology towards the creatures killed.

Major violence towards other human beings, and the kind of unfriendliness and nastiness that has been mentioned so far, seem to be associated much more with relatively advanced societies. The Twentieth Century was, I'd, say the most violent century we have had so far, especially when the slaughter on the roads is added in, and the signs seem to be that the 21st century could well turn out even worse.

I'd suggest that the reasons for this are likely to be the ones mentioned - people crowding in on each other, so that as a protective mechanism we draw our boundaries between our in-group ("us") and the rest (them") ever tighter. On top of that there are technological changes that can amplify our anger and make it lethal. (Assault rifles instead of fists or even knives, cars instead of Shanks's pony.)

Though in fact a lot of the violence we see is probably not so much to do with anger, but rather with power. Wars don't normally happen because people get angry. They start for quite other reasons, and then the anger is built up to keep things going.