Harsh, but true
This argument is both empirically and rationally impeccable:
If you cooperate to kill and eat large animals, that is a lot more cooperation than if you live on fruit, nuts, and insects.
If you cooperate to make war and genocide, that is a lot more cooperation than if you cooperate to kill large animals.
Chimps and men kill and eat deer, monkeys and suchlike. Chimps and men make war. Therefore the common ancestor of chimps and men made killed and ate large animals, and made war – was a killer ape. The ancestors of men are that branch of the lineage that ate meat more heavily, the ancestors of chimps are that branch of the lineage that ate meat less heavily.
Cooperative killing is the killer application for intelligence.