This is not such a big stretch. — Brett

News to me, but not any surprise. I'll bet they're careful about their language and how they construct and interpret their experiments and observations.

Most societies have justifiable homicide. We'd have to interview that apes. The issue is whether the killing was within their moral norms,(and not ours). Do they think that certain kinds of leadership excess deserve the death penalty.

The issue is whether the killing was within their moral norms,(and not ours). — Coben

From what I’ve read actions like this are not within their norms. There has even been the theory that it’s the imposition of humans on their environment and consequently behaviour that has caused this behaviour. That now seems to be in doubt, but not, I imagine, total. So I don’t believe it is within their normal behaviour. By that I mean the destruction of the tyrant chimp by such vicious aggression is not the same as displays of aggression or some physical contact to drive off opponents.

So this action is extreme and unusual, but still something they were capable of. It’s not as if they were taught how to kill on these grounds, anymore than we were, which is my point. Where did they get the idea of going from displays of aggression to brutal killing like this? It’s something they may have always done but we never knew it. But they obviously can do it.

rom what I’ve read actions like this are not within their norms. — Brett

It was rare, but then perhaps the leader ape's behavior had been rare. Justifiable homicide is fairly rare also, but it still falls inside moral norms. I suppose even the leader's behavior might have been at an extreme end of norms. IOW I think, in general, humans can murder, but not animals. Unless they have been clearly part of devastated societies and they have societies. LIke the elephants that have been raping even Rhinos, but they've come from devastated packs and had no parenting, this due to humans. I think humans, with their ability to coldly calculate long term gains and so on can decide to go outside the norms of the group and murder. I think it can make sense to speak that way about us. Animals - and I give animals more credit than most humans do for being capable of things we are - I don't think have criminals in the same sense we do.

How would it be defined without the help of the law? — Brett

Laws are about social organization. Otherwise, without laws it simply would be that people wouldn't like one killing another. I don't like that and you don't like that. I guess many would oppose that. You don't have to have a law for that. But with a law, you have the constructs of an society with formal institutions. Killing and murder are two different definitions.

Many see in animal group behavior some kind of proto-society from where our society has developed. That may be, but how much the behavior of other primates can say about us is not so simple. We differ a lot from animals, thanks to our advanced language skill and advanced co-operation.

We don’t really know why humans murder. If we don’t know that, or can’t reach agreement, then I can’t see why we can say other primates don’t murder.