Dry Habitat Chimpanzee Ecology and Behavior: Implications for Human Bipedalism

大多数人类古生物学家认为两足行走是原始人的决定性特征，但对于这种主要适应是如何以及为什么进化的，人们几乎没有一致意见。作为人类的近亲，黑猩猩可以提供行为和生态方面的线索，帮助我们了解人类血统的早期进化。在这里，PI建议习惯和研究一个特别合适的黑猩猩群体，以测试一些两足动物起源的假设。早期的原始人表现出人类和类人猿的混合特征。他们可以被粗略地描述为腰部以上像黑猩猩，腰部以下像人类。对贡贝和马哈尔黑猩猩的研究可以解释这种奇特的特征组合。在这些地方，当黑猩猩以矮树上的小果实为食时，两足行走最为常见。这些树大多位于黑猩猩生活范围最干燥的地方。在地面上，黑猩猩站起来从最低的树枝上摘这些水果。当他们在树上采摘果实时，他们一半用两足站立，一半用一只胳膊吊着。导致黑猩猩两足行走的树木是在它们活动范围中最干燥的地方发现的，这一事实很有趣，因为早期的原始人生活在类似的干燥栖息地。两足动物不太可能进化成以这些水果为食的动物，除非这些水果非常丰富。因此，我们可以预期，小水果在今天干燥的栖息地比在潮湿的栖息地更丰富。PI计划在乌干达塞姆利基谷野生动物保护区的干燥森林中研究黑猩猩，以确定塞姆利基是否比潮湿栖息地有更多的小直径果实，以及干燥森林的黑猩猩是否比其他黑猩猩更适合两足行走。

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.