Debate has long raged in the scientific community over the origins of bipedalism; specifically the time period when it came about and the reason that humans’ apelike ancestors came down from the trees and began walking on the ground. Since the 1970s, it has been widely speculated that Australopithecus afarensis, the most famous example of which is the fossil named Lucy, spent about half the time climbing in the trees and half the time walking. But a foot bone discovered in Ethiopia may tilt the equation more in the favor of upright walking and provide evidence that total bipedalism may have come about much earlier than previously thought.
3.2 Million Year Old Arch Bone
In research conducted at the University of Missouri in Columbia, lead researcher Carol Ward analyzed a bone found in a fossil site in Hadar, Ethiopia. The bone appeared to be from the outside arch of a humanlike foot; it was similar in size and shape to the bone near the little toe in modern human beings. The fossil was dated to about 3.2 million years old and identified as belonging to a specimen of Australopithecus afarensis, a small hominin ancestral to modern humans.
The discovery of an arch from a foot bone is another strong indicator that the species spent a great deal of time walking upright, as arches make it difficult to climb in trees the way other ape species do.
Australopithecus Afarensis and Bipedalism
Anatomical evidence indicates that A. afarensis was at least partially bipedal. It had a pelvis that was shaped more like a modern human’s than that of a tree-dwelling ape; its big toes and lack of a grasping hindlimb also suggest that A. afarensis spent much of its time on the ground.
But there are features that point to some amount of tree-living too, such as long arms and a more climbing-oriented shoulder joint, not to mention the structure of the skull, which is not conducive to bipedalism. Because of this mix of features, researchers concluded that A. afarensis was partially ground-dwelling and partially tree-dwelling.
Laetoli Footprints
The earliest evidence that Lucy and her kind were bipedal were the famous footprints in Tanzania, fossilized in volcanic ash. These footprints, dated to the same time period that A. afarensis were alive, clearly showed evidence of arches, though since very few fossils of hominin foot bones have been uncovered, it is uncertain whether the footprints actually belong to another species.
While there is still a great deal of speculation about the new arch bone discovery, with some researchers pointing out that the single fossil is not enough evidence to base an assertion of nearly total bipedalism upon, the evidence does seem to be mounting that humans’ ancient ancestors may have come down from the trees much sooner, though the reasons for this are still not entirely understood.
Source:
Welsh, Jennifer. "Foot Bone Puts Prehuman Lucy on a Walking Path." LiveScience. 10 Feb. 2011. Web. 02 Mar. 2011. http://www.livescience.com/12805-human-ancestor-foot-bone-bipedalism.html.
Jenny Ashford - Jenny Ashford is a writer and graphic artist from central Florida. Her main area of interest in her Suite 101 articles is science, with a ...
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