The world took notice in 2007, when Iowa State University anthropologist Jill Pruetz announced the discovery of African chimpanzees who use sharpened sticks to hunt smaller animals — an activity previously deemed exclusive to humans.
But exactly how the chimps make and use their tools of death was less certain until Trisha DeWitt showed up. It took a month of preparation in Costa Rica, six weeks in Senegal’s 100-plus temperatures last summer and further research back on the UIndy campus during the past year, but DeWitt, who is just completing a master’s in human biology, thinks she has some answers.
On a thesis project advised by UIndy Professor Christopher Schmidt, DeWitt spent 160 hours observing, photographing and shooting rare video of the tool-making chimps at Pruetz’ National Geographic-supported research and conservation site in the savannas of western Africa.
She noted, among other things, that chimps of all ages in the small community make their tools quite methodically, breaking off live branches of a certain length, then stripping and sharpening the sticks by running them side-to-side through their teeth like violinists. On the hunt, she says, a chimp will forcefully drive the pointed end into a tree cavity in hopes of striking some prey — most likely an adorable bush baby — then pull the tool out to sniff or lick for clues.
“They don’t use the tool to kill the bush baby,” DeWitt says. “They only use it to detect if it’s there or to immobilize it.”
To complete the project, she also collected several teeth from deceased chimps for analysis using the UIndy Department of Anthropology‘s white-light confocal imaging profiler, a sort of high-tech microscope that Schmidt obtained with a grant from the National Science Foundation.
Electronically viewing the tooth surfaces at high magnification, she found not only the vertical etching that occurs from eating, but also deep horizontal grooves on the rear side of the incisors, suggesting that the chimps use their very front teeth, not their molars or premolars, to shape the sticks. The findings could suggest new approaches to the study of early human development.
“This is very preliminary,” says DeWitt, who grew up in Greene County. “I’m building a basis for future research that can bridge the gap between primatology and dental microwear studies.”
Learn more about the tool-making Fongoli chimps here.
