September 1, 2005 | David F. Coppedge

Chimpanzee Fossil Upsets Early Man Speciation Theory

Paleontologists need no longer lament the complete dearth of chimpanzee fossils.  Nature announced the discovery of the first fossil chimpanzee teeth.  The location, however – the Great Rift Valley in Africa – was unexpected.  The discoverers, Sally McBrearty and Nina G. Jablonski,1 explain:

There are thousands of fossils of hominins, but no fossil chimpanzee has yet been reported.  The chimpanzee (Pan) is the closest living relative to humans.  Chimpanzee populations today are confined to wooded West and central Africa, whereas most hominin fossil sites occur in the semi-arid East African Rift Valley.  This situation has fuelled speculation regarding causes for the divergence of the human and chimpanzee lineages five to eight million years ago.  Some investigators have invoked a shift from wooded to savannah vegetation in East Africa, driven by climate change, to explain the apparent separation between chimpanzee and human ancestral populations and the origin of the unique hominin locomotor adaptation, bipedalism.  The Rift Valley itself functions as an obstacle to chimpanzee occupation in some scenariosHere we report the first fossil chimpanzee.  These fossils, from the Kapthurin Formation, Kenya, show that representatives of Pan were present in the East African Rift Valley during the Middle Pleistocene, where they were contemporary with an extinct species of Homo.  Habitats suitable for both hominins and chimpanzees were clearly present there during this period, and the Rift Valley did not present an impenetrable barrier to chimpanzee occupation.   (Emphasis added in all quotes.)

The teeth, estimated by radiometric methods to be around 500,000 years old, were found within 1 kilometer of a hominid fossil site.  This should not be surprising, since scientists believe chimpanzees ranged over a much wider area than the past; their restricted habitats today are due partly to pressure from human occupation.  The area where the three chimp teeth were found has revealed fossils of many other large and small mammals, including monkeys.  The authors explain what this means to evolutionary theory:

This evidence shows that in the past chimpanzees occupied regions in which the only hominoid inhabitants were thought to have been members of the human lineage.  Now that chimpanzees are known to form a component of the Middle Pleistocene fauna in the Rift Valley, it is quite possible that they remain to be recognized in other portions of the fossil record there, and that chimpanzees and hominins have been sympatric since the time of their divergence.

By sympatric, they mean that the lineages diverged in proximity, without being geographically isolated (allopatric).  Sympatric speciation was until recently viewed as heretical (see 01/15/2003 entry); now, paleoanthropologists will have to come up with new ideas for why humans diverged from the great apes, given that they apparently shared the same habitat.  See also News@Nature, BBC News, and MSNBC News.

1McBrearty and Jablonski, “First fossil chimpanzee,” Nature 437, 105-108 (1 September 2005) | doi: 10.1038/nature04008.

Part of the reason none have been found in this area before is that paleoanthropologists were not looking for them.  McBrearty said that now we know they are there, researchers “will start looking for them,” implying that the favorite story of human divergence through migration to the grasslands blinded their eyes to the possible presence of chimpanzee fossils in the Great Rift Valley.  Since this was the hotbed of hominid bones that made the Leakeys famous, hunters wanted missing links, not existing species of chimpanzees.
    This announcement will not frustrate Darwinists very much.  They actually enjoy new twists to the plot of their favorite story.  Maybe some will say the Homo neighbors brought the chimp back from a hunt in the jungle and had it for dinner, spitting out the teeth.  Most likely this will give a temporary boost to the internecine heresy of sympatric speciation, but it will be harder to come up with a reason why Pan and Homo diverged so much if they lived in the same vicinity.  Maybe it will also revive the simplistic Larry King question, “If we evolved from apes, why are there still apes?”  The answer is, of course, that some of them had a choice.
    Sharp minds will notice that there is no evolutionary evidence here.  The Homo fossils were described in the BBC piece as “probably” an advanced form of Homo erectus, whatever that vague category means (see 07/03/2004 entry).  They “looked like people and were a fairly sophisticated culture with various stone tools and lived in the same environment as humans.”  If they looked like people and and acted like people, why even differentiate them from people?  There are Homo sapiens sapiens today that share that same habitat and match that same description right now.  People come in a variety of sizes and shapes, but are all one species of people.  What’s evolution got to do with it?

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Categories: Early Man, Fossils

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