> Ecology and society determine how we realize those traits - in times of intense competition, we resort to tribal warfare. In times of plenty, we cooperate. E

> Ecology and society determine how we realize those traits - in times of intense competition, we resort to tribal warfare. In times of plenty, we cooperate. Ecology creates evolutionary pressures for a genetic predisposition to tribal violence. Those genes are still there in times of abundance. They might be activated less in times of abundance, though. I agree with the "society" part of your comment. Sapolsky's study of Bonobos shows that cultural change via the death of alpha males can have a lasting impact on the level of violence in later generations.