Tuesday, September 20, 2011

You Look Familiar: Another piece of humanity's family tree is fitted into place

In 2008, scientists found the fossils of a new australopithecine species, Australopithecus sediba, in a cave in South Africa. Dr. Lee Berger of the University of the Witwatersand, in Johannesburg led the research. He first concluded that the species came too late in the fossil record to be an ancestor of the Homo lineage. However, further research into the specimen has revealed that sediba did predate Homo erectus. He also found that parts of its anatomy are similar to that of modern man.

X-rays of the interior of the skull showed that the size of the brain was consistent of that of other australopithecines, but the shape of the brain was more like that of a modern human brain. In particular, the frontal lobes, the site of higher cognitive function in humans appeared more humanlike in sediba's brain than in the brains of other australopithecines. Scientists previously thought that these kinds of neurological changes, which eventually gave rise to humanity, occurred after the expansion of the brain. However, these studies suggest that the changes predated this expansion. Additionally, studies of the fossils show that this australopithecine walked upright and had an upright, butterfly shaped pelvis, like that of a human. Scientists have long debated whether bipedalism or giving birth to babies with large heads drove the changes in the shape of the human pelvis. Sediba adults, and so likely their children, had small heads, suggesting that walking upright was the advantage attained first by the modern pelvis.

With these discoveries, Dr. Berger now posits that sediba may have evolved from an earlier Australopithecus species directly into Homo erectus. This would mean that Homo habilis, which was previously thought to be a transitional form between Australopithecus and erectus, was not an early human, but an evolutionary offshoot, and not a part of the genus Homo.


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