InformedHealth.org How does our sense of balance work?
To walk upright successfully needs a fully functioning balance organ in the inner ear, as anyone suffering from Ménière's disease will testify, so the study of the origins of bipedalism in the remote ancestors of humans needs to take into account changes in the inner ear that would facilitate it.
Humans and our closest relatives, the great apes and the simians, display a range of locomotion but only humans are normally fully bipedal, although chimpanzees can use bipedal locomotion when carrying a load for example.
The monkeys normally run along branches on all fours, balanced on top of them and jumping from branch to branch; the apes hang beneath the branches in locomotion known as brachiation, but humans are ungainly in trees and prefer bipedal locomotion on the ground. The question is, when did this ability evolve in our ancestry?
We can be sure our hominin ancestors the Australopithecines, were fully bipedal because we have a record of their footprints in volcanic ash at Laetoli, and their lower limbs and feet were almost indistinguishable from those of Homo sapiens. 'Lucy' (Au afarensis) was probably mostly bipedal but may have taken to trees for safety and possibly to sleep on constructed platforms like chimpanzees do. The evidence of injuries to her fossilised skeletal remains suggests she may have died by falling out of a tree.
To investigate this stage in our evolution a group of researchers, led by Professor Xijun Ni, which included Yinan Zhang, a doctoral student, both of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences (IVPP), and Terry Harrison, a New York University anthropologist, used 3-dimensional CT scanning to examine the inner ear of a 6-million-year-old fossil ape, Lufengpithecus, unearthed in China’s Yunnan Province in the early 1980s, and compared it to the inner ear of other living and fossil apes and humans from Asia, Europe, and Africa.
The formation the fossil was found in has been previously dated magnetobiostratigraphically to about 6 million years. This technique depends on the record of periodic changes in Earth's polarity trapped in magnetic particles in sedimentary rocks and by recording the microfossils such as pollen associated with these changes:





































