gorillas are not tree-dwellers. They stay on the ground amongst their families.

You sure about gorillas, and you're not talking about, maybe, the chimps? Yes they're cousins but the chimps are the more violent ones. Chimps they kill each other and some of them eat their own.

Here's an excerpt I got from a site: "...silverbacks may kill young not sired by them, but otherwise, gorilla family life is mostly peaceful. Bloody battles sometimes occur between silverbacks when they square off to compete over female groups or home ranges". Here's the link: http://nationalzoo.si.edu/Animals/Primates/Facts/FactSheets/Gorillas/def....