we, as a race, aren't nearly as evolved as we would like to think, and things like this are just the proof. monkeys will sometimes pick one monkey, and murder it....the "tribe" isn't happy, food is scarce, a predator is making them nervous, people are causing their habitat to shrink...when the stress reaches a peak, one unlucky monkey makes a mistake, and the whole tribe rips them to shreds....then things go back to close to normal.....for a while, till the stress builds up past the safety point again.....
sounds familiar to me...