Knowing that modern human bipedalism is unique among primates (and other mammals), Fred Spoor and colleagues decided to evaluate the vestibular apparatus of the inner ear. An area designed to help coordinate body movements. Modern human locomotor activity requires that the vestibular apparatus of the inner ear be able to maintain body posture, even though we are constantly balancing all of our weight on very small areas of support. Anyone who has suffered vertigo knows firsthand just how crucial this area is for balance and everyday activities. Using high-resolution computer tomography, Spoor, et al., were able to generate cross-sectional images of the bony labyrinth that comprised the inner ear. They wrote: “Among the fossil hominids, the earliest species to demonstrate the modern human morphology is Homoerectus. In contrast, the semicircular canal dimensions in crania from southern Africa attributed to Australopithecus and Paranthropus resemble those of the extant great apes. (1994, 272:645).” With that single declaration, Spoor and his colleagues have drawn a line which unequivocally states all fossils prior to Homoerectus have ape-like morphology that allowed them to climb trees, swing from branches, or walk hunched over on their knuckles. So, not only were the ribs, pelvis, limbs, hands, and feet of this fruit eater chimp-like, but there also is evidence which suggests that the organ required for balance in Australopithecus afarensis was chimp-like as well.
“Lucy Dethroned” Bert Thompson and Brad Harrub. Reason and Revelation May 2003 (Apologetics Press)