This does not actually speak to the utility of such instincts to individuals. Rather, it indicates their utility the gene bundle, by increasing the genes' probability of propagating. A tribe that stole from itself would not get very far through time.
Yeah, but group selection doesn't make a very big difference, as discussed in The Tragedy of Group Selectionism.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.