August 27, 2007
Re-Dating the Split
Posted by scott at August 27, 2007 11:42 AM
New fossil finds seem to indicate the hominid-chimpanzee split took place much earlier than previously thought. Two things to note: the pittance of remains that are at the center of examination. At one point our ancestors were so thin on the ground a few teeth and a broken jaw is all that's left of them.
The other is much more important: fossil evidence that seems to decisively prove there are problems with using genetics to date events in the evolution of humans at least, perhaps others as well. The 6 mya date of the chimp/human split has always been controversial with anthropologists, since conventional wisdom at the time (the early to mid 80s, as I recall) said such a major evolutionary event would've happened much earlier. However, the geneticists had science and repeatability on their side... every time the tests were run, they came out with the same number, and so the conclusion was gradually accepted.
Fossil evidence that directly refutes this cornerstone of genetic paleoanthropology is earth-shaking indeed. However, in spite of what supporters say, it will be many years indeed before this finding becomes widely accepted. A few bits of mineralized bone have indeed overturned long-held beliefs before, but they don't do it often and they never do it quickly. It may yet turn out some mistake has been made which will allow the genetics-based date to stand.
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Bah - they give no real input as to how the actual dating was done. Was it direct or indirect? Indirect dating can lead to incorrect results, IIRC (since you're testing the material around the item and not the item itself, there's a chance the assumption of "same age" for the two doesn't hold). Secondarily, that all of the appropriate characteristics in the teeth aren't there, as they should be, leaves open some chance that we could be looking at a "dead end" species that didn't survive or a completely new species.
As for the reliability of genetic evidence, it's pretty solid. Mutations in the DNA occur at a very regular interval, time-wise. The timing doesn't really vary in vertebrates (regardless of species), so no real problems there.
Not that geneticists can't be wrong due to other factors, but that one's pretty well proven.
Scientists use a wide variety of direct and indirect methods, which have been used to accurately return information on the ages of buried and preserved remains we can tell the age of (fossilized remains of ancient but not prehistoric people, mostly). Obviously, some of those methods need to be re-evaluated, but the question is, which ones? Geneticists have been wrong too, after all.
I agree that geneticists have been wrong before and we'll be wrong again. That being said, the article was woefully short on the details that'd let us establish where error might lie. If they used a good sample of both, the dating is likely correct. My assumption is that they probably did as much as possible. From there, it rolls on to the interpretation of the actual fossils, which seems to be a bit shakier, at least from what the article stated.