Science Friday
02-23-07
MATERIAL GIRLS
Small prey, beware—young female chimps in Senegal, a country in west Africa,
were spotted making spears for hunting, according to a paper published in the
journal Current Biology this week. This is the first time anyone has recorded a
non-human animal making and using a tool to hunt.
Tool use in mammals is well-documented: primates crack nuts with rocks and
naked mole rats have been seen holding woodchips in their mouths to dig.
“Chimps are probably best known for termite fishing,” says Jill Pruetz, a
professor of anthropology at Iowa State University and first author on the
study. “And they definitely do that at my site.” To termite fish, a chimp pushes a
vine or a stick into a hole in a termite mound and pulls out a snack.
But the chimps that Pruetz studied did more than fish for termites: they fashioned
spears—even sharpening the tip of the branch with their teeth—to hunt small
nocturnal primates, called bushbabies.
Bushbabies, which look like a cross between a raccoon and a squirrel and are
“about the size of a grapefruit,” says Pruetz, spend their days sleeping in the
hollows of trees. Despite their daytime snoozing, bushbabies are hard to catch.
They are quick and can bounce from limb to limb, and are capable of moving
unpredictably in three dimensions, Pruetz says.
The chimps were seen forcefully jabbing their homemade spears in bushbabysleeping-holes. Pruetz believes that the chimps were trying to immobilize the
bushbaby, not necessarily skewer it. Post jabbing, the chimp would break the
branch where the little primate was sleeping, and try to dig out dinner.
Chimps in other communities don't eat bushbabies, preferring red colobus
monkeys. But the community Pruetz studies don’t have access to red colobus
monkeys—the savannah seems too dry for them. The absence of preferred prey
might have sparked this novel tool use. Pruetz says: “There are different
pressures associated with this environment. They have to come up with creative
solutions.”
The toolmakers were mostly young females, suprising because in chimp society,
adult males are the primary hunters. As the hunters, the males also eat first. But
bushbaby hunting is “a niche they don’t exploit,” says Pruetz. Because these
young chimps can’t compete with elder males for food resources, they appear to
have found their own source.
This finding supports the idea that innovations, in human evolution as well, may
come from non-dominant groups. Although Pruetz isn’t willing yet to give females
credit for inventing the wheel, she says, “males can overcome problems in one
way, and females are almost forced to be innovative in getting to the problem in a
different way. I wouldn’t say brawn versus brains, but some people have really
dichotomized it that way.”
-Flora Lichtman