Convincing someone to go kill other people so you can get their stuff is a lot harder. You have to get creative with the reasons, and even then you had better be giving those fighters their cut unless you've really managed to get them fully committed to whatever excuse to made up. It helps a lot if there is some kind of wedge issue you can exploit, which is where religion and ethnicity come in handy.
We've known for decades that chimpanzees go to war, and during that war will happily slaughter each other.
Why is it weird? Religion, ethnicity and political beliefs are argued all the time, even here on HN, as the reason for why shit happens.
Also, what is a "blood feud" in the primates? Chimps seeking revenge for the murder of another Chimp? Why was the first Chimp killed then? I think "blood feud" is a good start, but why? The paper sort of explores possible reasons.
> Supposedly academic anthropology had difficulties accepting these findings, especially the Yamomamö studies by Chagnon where he documented them going to war to steal each other's women, as it contradicted the popular idea of the noble savage.
I don't know what you mean, the "noble savage" is a discredited racist trope. Chagnon is worth considering but surely you're aware of the academic criticism of his work and methods? It wasn't because of the "noble savage", that would be a lazy dismissal of the criticism. He didn't have the final word on the topic.