Humans aren't the only ones who hunt with weapons -- a troop of chimps in the wild have been observed crafting sharp spears to stab their prey.
The technique, described in the latest issue of the journal Royal Society Open Science, could have originated with the common ancestor of humans and chimps, suggesting that the earliest humans hunted in a similar manner.
The chimps spent time making the deadliest, most effective spears.
"The tools (spears) are made from living tree branches that are detached and then modified by removing all the side branches and leaves, as well as the flimsy terminal end of the branch," lead author Jill Pruetz told Discovery News.
"Some individuals further trim the tip of the tool with their teeth," added Pruetz, who is a professor in the Department of Anthropology at Iowa State University. "They average about 75 centimeters (around 30 inches) in length."
Pruetz and her team watched chimpanzees from a site called Fongoli in southeastern Senegal, West Africa, making spears in this manner.
Spear in hand, the chimps would sneak up on bushbabies -- small, big-eyed primates -- and stab them to death. Bushbabies, which are nocturnal and are also called "galagos," spend much of their days snoozing in tree cavities. They can become an easy filling meal for a spear-wielding chimp.
The researchers noted that female adult chimps made and used spears more often than adult males. The males relied more on their size and strength for hunting. Female chimps are almost always hindered by infants that ride on their backs or bellies, so spear hunting is far more effective for them than attempting to chase down prey.
The researchers suspect that a female primate invented the world's first spear.
"In a number of primate species, females are the innovators and more frequent tool users, so I think it is possible that a female invented this technique," Pruetz said.
Dominant males at Fongoli support females and younger males by allowing them to keep their own kills, she added. This is rare, as in most chimp troops, large males steal prey from subordinates.
The Fongoli chimps are the only known non-human primates that systematically hunt large prey with weapons, so the site itself is of interest to the researchers. It is a savanna with a dry season that lasts over seven months. Early humans might have faced comparable conditions that led to greater reliance on meat consumption and efficient hunting methods.