Most human paleontologists recognize striding bipedalism as the defining attribute of the Hominidae, but there is little agreement as to how and why this primary adaptation evolved. As our closest relatives, chimpanzees can provide behavioral and ecological clues that will help us understand the early evolution of our lineage. Here, the PI proposes to habituate and study a particularly appropriate chimpanzee community in order to test a number of bipedalism origin hypotheses.
Early hominids display a mix of human and ape-like characteristics. They can be described crudely as chimpanzee-like from the waist up, and human-like from the waist down. One explanation for this curious mosaic of traits derives from research on Gombe and Mahale chimpanzees. At these sites bipedalism was most common when chimpanzees fed on small fruits in short trees. Such trees were mostly located in the driest part of the chimpanzee range. On the ground chimpanzees stood up to pick these fruits from the lowest branches. When they gathered fruits in the trees they fed partly standing bipedally and partly hanging by one arm. The fact that trees that elicit bipedalism in chimpanzees were found in the driest part of their range is intruiging, since early hominids lived in similar dry habitats. Bipedalism is unlikely to have evolved for feeding on such fruits unless they were abundant. We might therefore expect that small fruits are more abundant in present-day dry habitats than in wetter habitats. The PI proposes to study chimpanzees in a dry forest in the Semliki Valley Wildlife Reserve, Uganda in order to determine whether Semliki has significantly more small-diameter fruits than wet habitats, and whether dry-forest chimpanzees are more bipedal than other chimpanzees.
