Chimps in Uganda take up arms - The Wife Beaters of Kibale
From Time.com: "Until now, devising tools to inflict pain and death seemed to be something only humans did. To be sure, lots of animals use tools. Sea otters employ rocks to crack open shellfish. Crows in New Caledonia extract insects from foliage with twigs—or even bent wire—held in their beaks. Chimps will use sticks and stones for all sorts of purposes, including flailing and throwing them to impress rivals. But for all the theatrics of these so-called threat displays, no one before now had ever seen an ape use a stick to beat another ape."
"There are sound evolutionary reasons for this. Predators don't need weapons; they are weapons. During internecine wars, chimps will rip one another apart with their teeth and hands. Indeed, a good deal of evolutionary ingenuity has gone into the development of greeting and submission rituals to ward off lethal aggression."