* Astronomy

 Published the week of Nov. 12 in the online early edition of the Proceedings of the National Academy of Sciences, the study documents the use of digging tools among chimpanzees inhabiting the Ugalla region of western Tanzania. An arid woodland savannah, Ugalla is thought to be an environment similar to those exploited by hominids that eventually evolved into modern humans.
James Moore, a biological anthropologist at the University of California, San Diego, who has been coordinating research at the site since 1989 under the aegis of the Ugalla Primate Project, said the findings are important because they show that digging with sticks is not a uniquely human adaptation and also because they provide additional insights into the role a dietary shift may have played in hominid evolution.
The study is co-authored by Moore with Travis Pickering of the University of Wisconsin-Madison. R. Adriana Hernandez-Aguilar is the first author. Hernandez-Aguilar gathered the field data as part of her dissertation research at the University of Southern California.
Changes in the teeth and jaws of the first chimp-like hominids provide evidence of a dietary change to something requiring heavy chewing some 3 to 4 million years ago, but the nature of the change is hotly debated. Nuts and meat, along with what scientists collectively call plants underground storage organs (roots, bulbs and tubers) have all been identified as candidates for foods that enabled australopithecines to succeed in new environments starting some 4 to 5 million years ago. Contemporary hunter-gatherers make extensive use of underground storage organs with the help of digging sticks, but sticks decay rapidly and evidence of their use by hominids is unlikely to fossilize leading some researchers to focus on meat and hunting because stone points are preserved. The modern chimps of Ugalla, however, may provide clues to an alternative.

Chimpanzees are not australopithecines, and we can't conclude that if they do something today, our ancestors must have done it then. But, when integrated with research on the fossil and pale ecological record, modern analogies are useful for investigating our past.  In this case, the Ugalla chimpanzees suggest that underground resources were within reach of our ancestors with similar brain size and hand morphology.

While the researchers did not directly observe the chimps digging with tools, strong circumstantial evidence of the activity was found at 11 different sites in Ugalla. Ten of these sites, with multiple holes in the ground, were directly beneath chimpanzee nests and the other was nearby. Chimpanzees were further linked to these sites through knuckle prints, feces and wadges chewed-up, spit-out wads characteristic of chimps of the excavated tubers. No other mammals had left traces.

There were seven tools found at three of the sites. Worn edges and patterns of adhering sediment on the recovered sticks and bark, visible to the naked eye and later confirmed by microscopic analysis, imply their use as implements.
A surprise finding, Moore, Pickering and Hernandez-Aguilar write, was that the chimps only took advantage of the hidden resources during the food-rich rainy season, and not as a fallback in times of scarcity. That observation, Moore said, challenges our current hypotheses about the role of such foods in hominid evolution and may help reframe the scientific debate.
Also provocative is the observation that some of the plants the chimps were digging are not used as food by local people but only as medicine.

University of Southern California