DNA and Man's origin

by D wiltshire 126 Replies latest jw friends

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  rem

  Saint Satan,

  I was under the impression that mtEve is relative in time. Depending on when bottlenecks in population occur the mtEve for a species can change over time. This means that our mtEve now may be different than it was 50,000 years ago for Homo Sapiens (though this is probably unlikely). The same would be true for Neanderthals.

  That said, you are correct that an mtEve can be derived for any population, though for disparate populations or separate species, the mtEve would probably be very far back. It would be dificult to say with certainty how far back the mtEve for such disparate species would go... say for Homo Sapiens and Neanderthals it could go as far back as Homo Habilis (if Neanderthals and humans both decended from this species) or even back to when apes and homonids diverged a few million years ago. It just depends on the variability in in the mtDNA and the snapshot in time when you are doing the comparison.

  rem
• 

  Satanus

  Rem

  Agreed. Also, it seems that the degree of similarities between different present time races, neanderthals, chimps and whatever are determined by genetic scientists, according to their estimations, their opinions. It could be that their evaluations would be subjective. Unless of course similarities are based on a strictly mathematical percentage basis. Just a thought.

  SS
• 

  rem

  SS,

  Yeah, there does seem to be a rather large margin of error. I suspect there is a lot of subjectivity involved in making these estimations and that is why the estimates are still pretty controversial. mtDNA is not a tool that evolution can be calibrated from - it's not an independent method of dating. These models are, as hooberus pointed out, based on the assumption of evolution, the dating we have so far through the fossil record, and on estimated mtDNA mutation rates. Obviously there are quite a few variables that can be tweaked here and there to come up with different estimates.

  rem
• 

  Earnest

  hooberus said :

  The [London Times] article by Earnest gave a set of dates between 853,000 to 365,000 years ago [for the separation between modern human and Neanderthal]. I would be interested to see if these dates were calculated based on assumptions of humans and apes sharing a common ancestor.

  The London Times article was citing a letter in Nature magazine from Dr. William Goodwin on "Molecular analysis of Neanderthal DNA from the northern Caucasus". The original letter can be read at http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v404/n6777/full/404490a0_fs.html.

  I have written to Dr. Goodwin regarding this set of dates but have not yet received clarification regarding his methods. However, I do think that an earlier article on establishing the DNA sequence of Neanderthals ("DNA sequence of the mitochondrial hypervariable region II from the Neandertal type specimen" at http://www.pnas.org/cgi/content/full/96/10/5581) provides important information on the methods used. This article says :

  The date of divergence between the mtDNAs of the Neandertal and contemporary humans is estimated to 465,000 years before the present, with confidence limits of 317,000 and 741,000 years. Taken together, the results support the concept that the Neandertal mtDNA evolved separately from that of modern humans for a substantial amount of time and lends no support to the idea that they contributed mtDNA to contemporary modern humans.

  Dates of Divergences. For the estimation of the ages of MRCAs [Most Recent Common Ancestors] of different groups of mtDNAs, the observed nucleotide differences were corrected for multiple substitutions by using the Tamura-Nei algorithm. The resulting genetic distances and the estimated age of the modern human-chimpanzee split of 4-5 million years were used to calculate the substitution rate of 0.94 × 10 7 substitutions per site per year per lineage with 5.92 × 10 8 and 1.38 × 10 7 as the lower and upper confidence limits. These estimates are in reasonable agreement with previous rate estimations for the mtDNA control region. Using these rates, the age of the MRCA of the Neandertal and modern human mtDNAs was estimated to be 465,000 years, with confidence limits of 317,000 and 741,000 years. This age is significantly older than that of the MRCA of modern human mtDNAs, which, by the same procedure, was determined to be 163,000 years, with 111,000 and 260,000 years as confidence limits. Finally, the age of the MRCA of the mtDNAs of the seven chimpanzees and the two bonobos was calculated as 2,844,000 years (confidence limits: 1,940,000 and 4,534,000 years).

  However, mtDNA sequences from more Neandertal individuals are needed to obtain a better understanding of the extent of separation between the mtDNA gene pools of Neandertals and modern humans.

  Earnest
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  hooberus

  It seems to me that all of these dates have as an anchor point the alledged human/chimpanzee divergance of 4 plus million years ago.

  Interestingly this date was itself based on the assumption of evolution calibrated based on orang-utan fossils !

  So the dates of 200,000 for "eve" and 853,000; 365,000 for "neanderthals" etc. are ultimately based on an evolutionary interpretation of orang-utans !
• 

  rem

  The dating of orangutang fossils is not based on evolutionary interpretations. The dating of fossils is done by several independently calibrated and verified means. None of these dating methods are predicated on evolution. Some of the dating methods and principles were developed even before the theory of evolution was created. You would have to provide some pretty extraordinary evidence to show that the dating of the orangutang fossils is inaccurate. Beyond that, yes, the mtDNA dating is based on assumptions regarding mtDNA mutation rates, thus the margin of error. There is no reason, however, to expect an error so eggregious that the dating would reflect thousands of years rather than hundreds of thousands.

  rem
• 

  hooberus

  rem said: The dating of orangutang fossils is not based on evolutionary interpretations. The dating of fossils is done by several independently calibrated and verified means.

  My comment did not directly relate to the "dating of orangutan fossils" themselves, but to the fact that the alledged human/chimpanzee divergence date of 4 plus million years was calibrated based on oranguntan fossils.

  earlier I said:

  It seems to me that all of these dates have as an anchor point the alledged human/chimpanzee divergance of 4 plus million years ago.

  Interestingly this date was itself based on the assumption of evolution calibrated based on orang-utan fossils !
• 

  hooberus

  rem said:

  Beyond that, yes, the mtDNA dating is based on assumptions regarding mtDNA mutation rates, thus the margin of error. There is no reason, however, to expect an error so eggregious that the dating would reflect thousands of years rather than hundreds of thousands.

  These assumptions regarding mtDNA mutation rates, with their margin of error calculations are based on the assumption that humans/chimpanzees shared a common ancestor millions of years ago. However if this did not happen, then not only would the assumed mutation rates be potentially in error, but also the "margin of error" calculation (which is also based on the assumption of a shared common ancestor who lived millions of years ago) would also be invalidated.

  There is a tendency when people see figures such as "confidence limits of 317,000 and 741,000 years" to assume that the creature in question must be at least as old as the lower figure. However this is not necessarily true as even the lower figure is based on assumptions of a shared common ancestor living millions of years ago.
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  funkyderek

  These assumptions regarding mtDNA mutation rates, with their margin of error calculations are based on the assumption that humans/chimpanzees shared a common ancestor millions of years ago

  Hooberus, this is becoming rather an annoying pattern. You make a claim, someone refutes your claim clearly and specifically, you then repeat and rephrase the claim several times underlining irrelevancies ignoring all the evidence thrown at you. You seem to think that just repeating unfounded claims ad nauseum is a substitute for learning about the subject you're discussing and providing evidence and rational arguments to support your claims. It's not. Now make a case or stop wasting everyone's time.
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  Shemittah

  Well, I hear the BBC are bring the next instalment of its "Walking With..." series. It's amazing what sorts of things you can come up with when you have a computer graphics rendering program and a vivid imagination! Yes folks, its "Walking With Cavemen" (or was it "Apemen"?) Nice little earner this series - especially from a supposedly non-commercial television company. I see they are doing their bit to indoctrinate the younger generation into accepting they are only animals. Hey, don't you know they are already starting to de-volve into Neaderthals thanks to the great dumbing down in education, most of them already don't know how to make fire with sticks. Since they've just about rung this subject dry, the next instalment will probably be "Walking With Aliens". Now that I would like to see! ;0)
  
  Alex.