Captive orangutan locomotion and its relation to the origin of human bipedalism

Abstract

One of the prominent questions in paleoanthropological studies is the origin of bipedalism. There have been several hypotheses presented on the ancestral type of locomotion that predated bipedalism. These hypotheses include a terrestrial knuckle-walking quadrupedal ape, a brachiating hylobatid-like ancestor, a palmigrade terrestrial ape, and a climbing arboreal ape. Thorpe et al. present an extension to the climbing hypothesis with the data that they gathered from wild orangutans of the Gunung Leuser National Park in Sumatra, Indonesia (2006, 2007). They present the hypothesis that bipedalism originated with an arboreal ape similar to extant orangutans, and they provide that the orangutan locomotor data that they gathered supports this claim. This paper includes locomotor data that I collected from captive orangutans in the Fort Wayne Children’s Zoo. The two data sets are not correlative, but my observations of assisted and unassisted bipedalism in the captive orangutans lend some support to the climbing hypothesis. When considering the functional anatomy of the wrist and ankle of extant primates and extinct hominins, the answer still remains inconclusive.