The classic text book picture of human evolution extends over millions of years to a time when supposedly the first seeds of humanity were just beginning to take a foothold in north east Africa (Ref 1). Within this classical picture the discovery of superbly preserved adult skeletons in the Hadar region of Ethiopia has set the chain for human evolution back beyond 4 million years ago (Ref 1). The general appearance of these skeletons- described as being half ape half human- has lead scientists to refer to them not as humans but as hominids (Ref 1). With an overall height of approximately three and a half feet and a brain size that apparently more closely resembled that of chimpanzees, these early hominids are on the surface exactly what evolutionists would have wanted for an ape-human intermediate (Ref 1). And yet what is stunningly clear about these skeletons, today classified under the name of Australopithecus (meaning "Southern Ape"), is that they reveal an anatomy entirely consistent with a bipedal gait (Ref 1). In other words, they would have walked on two legs.
Hundreds of Australopithecine specimens have now been found around Hadar. Amongst the findings unearthed are a number of stone tools that indicate that Australopithecus would have been capable of technological innovation, using local resources and materials for his tool-making needs (Ref 2). Nevertheless, as paleontologist David Begun noted there is now evidence showing that a taxonomic group of hominids older than the Australopithecines existed (Ref 3). Known as Ardipithecus, this new group is thought to have lived approximately 6 million years ago (Ref 3). Some of the evidence for the existence of Ardipithecus is extremely sketchy. Yohannes Haile-Selassie and colleagues from Berkeley and the University of Tokyo, for example, have used specific features from only a handful of molar teeth found in Awash in Ethiopia to draw an evolutionary sequence of hominids that extends from early apes (Ref 4). Perhaps not surprisingly Begun has cautioned against drawing any conclusions because of what he called, "the level of uncertainty in the available direct evidence" (Ref 3). In fact Begun appears much happier with a so-called 'messier view' of evolution in which several taxonomic groups co-existed (Ref 3).
Messy or not, today samples of skulls dating back as far as 6 million years ago are causing much consternation amongst paleo-anthropologists worldwide (Ref 5). While recognizably fragmentary, the picture that is emerging is not one of a continuously evolving lineage but rather of a coexistence of different types of hominid (Ref 6). More spectacularly these early samples seem to demonstrate unequivocally that bipedalism already existed as far back as 6 million years ago even in an environment that would have been dominated by woodland and dense forest (Ref 5). This, notes science writer Ann Gibbons, sounds a crashing death-blow to the orthodox view that bipedalism arose as a result of climate change that forced apes out of trees into grasslands (Ref 5). Many skeptics believe that Ardipithecus, rather than representing the genesis of human evolution, might have been an ancestor of the chimpanzee (Ref 5).
What we also see from these hominid findings is the seemingly unshakable compulsion to place fossil specimens into a sequence that links homo to the apes even when the specimens do not fit into a 'clean' sequence. One case, Orrorin tugenesis ('Original Man', otherwise known as 'Millenium man') that dates to approximately 5.8 million years, appears to have been more man-like in several key points than the later Australopithecines (Ref 5). In order to get around this apparent temporal misfit some scientists have employed words like 'yo-yo evolution' to explain how such features may have been partially lost in australopithecus before returning later on in the evolutionary sequence (Ref 5). Others have hidden behind the smoke screen of 'extensive hominid diversity' implicit in the messier model to try and explain why anatomical features that would have been expected to appear later on in a theoretical evolutionary sequence in fact appeared earlier (Ref 6). They explain away such discrepancies on the basis that they are exactly what one would expect from a rapid diversification of hominids (Ref 6). All of this of course brings us to the question of why we should think that any of these specimens were ancestral to humans- precisely the question that Peter Andrews of the Natural History Museum in London has asked and for which we still need an answer (Ref 5). Indeed in the 1960's the late paleoanthropologist Louis Leakey and his son Richard Leakey challenged the basic assumption that Australopithecus was ancestral to the genus Homo. They regarded Australopithecus as a mere offshoot from an evolutionary tree with Homo extending much further back in time than the above reports suggested (Ref 7).
Perhaps the best kept specimen of a possible upright, walking hominid was uncovered in early 2005 by Haile-Selassie and Bruce Latimer of the Cleveland Museum of Natural History in Ohio (Ref 8). The specimen included many bones from the legs, pelvis and back all of which seemed to support the hypothesis that this early Australopithecine would have walked on two legs (Ref 8). If indeed bipedal walking represented the origins of the human lineage that evolved from an ancestral ape, what transitional intermediates would have lead to this new form of locomotion? Brian Richmond and David Strait of the Department of Anthropology at George Washington University attempted to answer this question on the basis of certain bone features in Australopithecus that they claim were associated with knuckle walking (Ref 9). Knuckle walking is how chimpanzees and gorillas get around and in simple terms describes how the backs of the fingers are used to support much of the body's weight. From their own studies, Richmond and Strait concluded that some early hominid species, "[retained] the derived wrist morphology of knuckle-walkers", and that therefore these early hominids must have evolved from a knuckle walking ancestor (Ref 9). Others such as biologist Mike Dainton from the Department of Human Anatomy and Cell Biology at Liverpool disagreed that the evidence necessarily indicated a knuckle walking ancestry adding that, "it is debatable whether form, function and adaptive significance should be so linked within a modern evolutionary framework" (Ref 10). While paleoanthropologist Jim Fleagle concurred with Richmond's and Strait's conclusion, Henry Potts of the Smithsonian Institute rightly questioned why an ancestor already adapted for other forms of locomotion would have needed to evolve an alternative method, such as walking on two legs, to be able to get around (Ref 11). Anthropologist Carol Ward from the University of Missouri in Columbia speculates that a bipedal mode of walking would have freed up the hands for carrying food across large distances (Ref 11). Yet in the absence of any common ancestor with which to work on, such ideas are of course pure speculation (Ref 11).
In 1984, the American Museum of Natural History in New York held an exhibition that showed several of what are considered to be key fossils relating to human evolution. This 'Ancestors' exhibition caught the public eye for several reasons not least of which was the fact that many of the displays on show were brought to the museum in a convoy of limousines under police escort after having been flown from around the world on first class plane seats (Ref 7, p.21). The reverence shown to these specimens revealed their iconic, almost godly-like status in a scientific field that is filled with emotions and deep-rooted sentiments about the 'facts' of human evolution. As the late Harvard anthropologist Ernest Hooton noted, this so-called 'ancestor worship' has become the greatest source of danger for an objective study of human origins (Ref 7, p.26). With discoverers of hominid fossils eager to identify primitive features that place their finds closer to a theoretical common ancestor with the apes while equally eager to identify features that establish an evolutionary relationship with modern man, what we end up with is undoubtedly a half-baked story of our past (Ref 7, p.26). According to science writer Roger Lewin, our own judgment of the evolution of man is tainted by our desire to portray progress as, "the epitome of evolution", with modern man becoming an example of progress from its ancestral ape, just as industrialization became an example of progress from darker times of our history. In all, the history of modern anthropology has been characterized by subjectivity with the experts seeing what they wanted to see in the evidence that they found. Even answers to the question of where the enigmatic ape-man would have lived- be it present day Africa or Asia- have depended very much on individual preconceptions of what this ape-man would have looked like (Ref 7, p.70-90).
2. Brooks Hanson (2005), Paleontology, Early Tool Makers, Science Vol 307 p. 18
3. David R. Begun (2004), The Earliest Hominins-Is Less More? Science Vol 303 pp. 1478-1480
4. Yohannes Haile-Selassie,Gen Suwa, Tim D. White (2004), Late Miocene Teeth from Middle Awash, Ethiopia, and Early Hominid Dental Evolution, Science, Vol 303, Issue 5663, 1503-1505
5. Ann Gibbons (2002), In Search Of The First Hominids, Science Volume 295 pp. 1214-1219
6. Bernard Wood (2002), Hominid Revelations from Chad, Nature Vol 418 p.133-135
7. Roger Lewin (1987), Bones of Contention: Controversies in the Search for Human Origins, Published by Simon and Schuster, New York
8. Ann Gibbons (2005), Skeleton of Upright Human Ancestor Discovered in Ethiopia, Science Science, Vol 307, p.1545
9. Brian G. Richmond and David S. Strait (2000), Evidence that humans evolved from a knuckle-walking ancestor, Nature 404, 382-385
10. Mike Dainton (2001), Palaeoanthropology: Did our ancestors knuckle-walk?, Nature 410, 324-325
11. Erik Stokstad (2000), Hominid Ancestors May Have Knuckle Walked, Science Volume 287 pp. 2131-2132
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