Otto Tellick writes:
But uniquely in the case of humans (and going back some unknown amount of time among our predecessors), some groups within the population may fail to propagate because they get killed by other humans.
Uniquely, Otto?
There are many animals which kill within the species, including the common chimps, but not (or rarely) the bonobos. Many intelligent mammals are not particularly known for killing within their species.
Bull elephants sometimes fight, but elephants in general were at very little risk of being killed by their own or by others before we came along, and the high intelligence seems to have more to do with complex and close social relationships.
Whether or not dolphins kill amongst themselves, I don't know, but I can't recall hearing of it.
A number of animals use, and in some cases arguably make, tools, but it is not central to their feeding processes. I think that the hypothesis that our ancestral group at some point found themselves in a situation in which basic tool use/making became central and essential might be more important. That combined with the necessity for group hunting with these tools would have driven growth in intelligence both in relation to tool making and the all important
communication, what this particular ape's trying to do now.
The tool use doesn't apply to dolphins, of course, so perhaps communication in social animals is the all important key, and the reason why wolves/dogs are smarter than the solitary cats.
Interestingly, I think we may find that it's a surprisingly small set of genes that makes the intelligence difference between us and the other great apes, but I'm not guessing at how many yet.