Monday, June 29, 2009
On the savannas of Senegal, chimpanzees have started hunting bush babies with spears.
By Mary Roach
Photograph by Frans Lanting
National Geographic Magazine
Daybreak is sudden and swift, as though an unseen hand had simply reached out and raised a dimmer switch. Cued by the dawn, thirty-four chimpanzees awaken. They are still in the nests they built the previous night, in trees at the edge of an open plateau.
A wild chimpanzee does not get out of bed quietly. Chimps wake up hollering. There are technical names for what I'm hearing—pant-hoots, pant-barks, screams, hoos—but to a newcomer's ear, it's just a crazy, exuberant, escalating racket. You can't listen without grinning.
These are not chimps you've seen in these pages before. They're savanna-woodland chimps, found in eastern Senegal and across the border in western Mali. Unlike their better-known rain forest kin, savanna-woodland chimps spend most of their day on the ground. There is no canopy here. The trees are low and grow sparsely. It's an environment very much like the open, scratchy terrain where early humans evolved. For this reason, chimpanzee communities like the Fongoli group—named for a stream that runs through its range—are uniquely valuable to scientists who study the origins of our species.
By 8 a.m. my chintzy key-chain thermometer says it's 90 degrees. Our shirts are marked by the same white salt lines that appear on people's boots in winter. Here it's salt from sweat. The plateau we're crossing is a terrain of nothing, of red rocks and skin cancer, with no trees to break the fall of equatorial sun. In our backpacks we each carry three liters of water. It was cool when we set out. By noon it will be hot enough to steep tea.
I'm not complaining. I'm making a point. Life on the savanna—even so-called mosaic savanna, tempered by patches of lusher gallery forest along the streambeds—is exceptionally harsh. If you are a primate used to greener terrain, you must adjust your behavior to survive. Our earliest hominin (meaning bipedal ape) ancestors evolved more than five million years ago during the Miocene, an epoch of extreme drying that saw the creation of vast tracts of grassland. Tropical primates on the perimeter of their range no longer had plentiful fruits and year-round streams and lakes. They were forced to adapt, to range farther in their search for food and water, to take advantage of other resources. In short, to get creative.
In 2007 Jill Pruetz, an anthropologist at Iowa State University, reported that a Fongoli female chimp named Tumbo was seen two years earlier, less than a mile from where we are right now, sharpening a branch with her teeth and wielding it like a spear. She used it to stab at a bush baby—a pocket-size, tree-dwelling nocturnal primate that springs from branch to branch like a grasshopper. Until that report, the regular making of tools for hunting and killing mammals had been considered uniquely human behavior. Over a span of 17 days at the start of the 2006 rainy season, Pruetz saw the chimps hunt bush babies 13 times. There were 18 sightings in 2007. It would appear the chimps are getting creative.
There are individuals who are uncomfortable with Pruetz's tales of spear-wielding chimps, and not all of them are bush babies. Harvard professor of biological anthropology Richard Wrangham, who has studied chimpanzee aggression in Uganda's Kibale National Park, has been skeptical. Wrangham is widely known for his "demonic male" theory, which holds that the savage murders carried out by male chimps while policing their turf are suggestive of a violent nature at the core of man. Primatologist Craig Stanford, author of The Hunting Apes, also downplays the importance of Pruetz's findings. "This behavior is fascinating, but the observations are so preliminary that it merits only a short note in a journal."
For further info, here is a PBS Nova presentation on the growing cultural intelligence of the greater apes.