The Fongoli chimpanzees live in a mix of savanna and woodlands where prey is not as abundant as in rain forests. There are no red colobus monkeys, and although the chimps do hunt young vervet monkeys and baboons, the much smaller bush babies are their main prey.

Dr. Pruetz argues that less food may have prompted both technological and social innovation, resulting in new ways to hunt and new social interactions as well. Humans evolved in a similar environment, and, as she and her colleagues write in Royal Society Open Science, “tool-assisted hunting could have similarly been important for early hominins.”

The tools in question are broken branches that Dr. Pruetz calls jabbing tools. The season for bush baby hunting is June, when the temperature may be well over 100 and the humidity is suffocating. The Fongoli chimps find the bush babies in their dens in trees. Chimps will stab and poke one of the small animals, sometimes wounding but not impaling it, until it comes out of its hiding place. The chimps will grab it, Dr. Pruetz said, and immediately “bite the head off.”

Females, even those with infants, and juvenile chimps can do this kind of hunting. The process does not put a premium on speed and strength as the chase does, so big males do not have an advantage. But there is more than technique and technology involved. There is social change.

By and large, said Dr. Pruetz, the adult males, which could take away a kill, show a “respect of ownership.” Theft rates are only about 5 percent. The chimps she studies also have more mixed-sex social groups than chimp bands in East Africa.

Travis Pickering, an anthropologist at the University of Wisconsin, said that with less food available it seems that the Fongoli chimps, “have to be more inventive” and that “these hunting weapons even the playing field for non-adults and females.”

Early hominins may have been in a similar situation, he said. Hunting among human ancestors “very quickly became a male-dominated activity,” he said, but “female hominins could very well have been the inventors of weapons.”

When it comes to getting food, deciding who does what depends on definitions. Collecting insects, for example, is defined as gathering, not hunting. In the case of the bush babies, however, though they are small, they struggle and flee, and will bite. Any bite, no matter how small, can pose the danger of infection, so the pursuit of bush babies qualifies as hunting, Dr. Pruetz says, and Dr. Stanford and Dr. Pickering agree.