

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.

6 Shocking Things About Chimps

"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.

Chimps Turn Sticks Into Swiss Army Knife of Tools

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.

A chimpanzee stabbing prey to death in a tree cavity.courtesy of BBC

Pruetz thinks it's possible that some early humans feasted on bushbabies too, in addition to scavenging and going after larger prey.

Biological anthropologist Travis Pickering of the University of Wisconsin-Madisonhas has extensively studied early members of the human family tree, such as Australopithecus robustusandHomo erectus.

He believes that simple wooden spears "evened the playing field" in terms of hunting by certain female primates and younger, smaller males.

Chimp Swats Down a Drone That Invades Its Airspace

"Vertebrate prey are less readily available to chimpanzees in Fongoli than they are at other, more forested sites, so the Fongoli chimpanzees got inventive and came up with a way -- that is, a weapon -- to ensure greater hunting success," he explained, adding that bushbabies bite when attacked, so the spear creates a safe distance between the hunter and the bushbaby's teeth.

While human hunting might have had humble beginnings involving stabbing small prey, Pickering thinks that early human males quickly took this to a whole other level by hunting in coordinated groups.

"Hunting large animals in groups is advantageous because of increased vigilance -- more eyes -- and the potential to recruit others for defense if one hunter gets into trouble," he said.

"Moreover, there's no getting around the fact that most males are bigger and stronger than are most females, and thrusting or throwing a spear into a big, thick-skinned antelope or zebra is going to require more power than stabbing a galago."