|As usual, thanks wikipedia|
Chimpanzees are our closest extant relatives on the evolutionary tree. Some anthropologists use chimps as model organisms to study how human societies may potentially have formed. I briefly mentioned one of the most famous anthropologists of this sort, Jane Goodall, in the post about the New Caledonian crows. Jane Goodall is famous for observing chimps in Gombe Stream National Park, in Tanzania making and using tools. She also observed chimps killing and eating smaller primates, a behaviour that was not previously suspected.
Importantly, the Gombe chimps are forest dwellers, but early human ancestors were most likely savanna dwellers. This means that in order to understand early human evolution it is more appropriate to study model organisms inhabiting a similar habitat. Jill Pruetz of Iowa State University recognised this, which led her to study a group of savanna dwelling chimps in Senegal. Here she made some remarkable observations. Like the Gombe chimps, the chimps of Fongoli make tools to 'fish' for termites. In addition to the fishing however, the Fongoli chimps make 'spears' for hunting. The chimps, mostly females it seems, roughly sharpen sticks with their teeth to make rudimentary spears to poke into the sleeping holes of bushbabies. If the chimps detect blood on the spear they smash open the hole to retrieve their prey.
Evolution is largely driven by environmental factors. In forests the monkey population is large, but in the savanna woodlands monkeys are scarce. Jill Pruetz says that "hunting bush babies is a creative way to get protein", and speculates that the reason that females engage in this activity more commonly than males is that females are slower and often weighed down by infants, making hunting monkeys difficult.
National Geographic has some absolutely beautiful photos and videos of the Fongoli chimps. If you don't have time for the videos (I could only get the first one to load), you should definitely look at the photos.