Evidence for evolution, Installment 3a: Mitochondrial DNA and Neandertals

by seattleniceguy 48 Replies latest jw friends

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  Midget-Sasquatch

  Hooberus

  First I want to apologize for my curt answer to your valid question. You're right that the commonly accepted mutation rate for human mtDNA (2-4% per million years) was calibrated using the fossil record and the tentative age of the human chimpanzee split.

  Then you politely asked for some sources, when I and others said that chimps didn't have anything to do with it at all.

  I like a hot headed lug just ranted on without giving you a source. Well here goes:

  Why I said that chimps really didn't have to do with it, is because of what I read in the following paper: Nature, 325 (1987), 31-6.

  from page 33

  Tentative time scale

  A time scale can be affixed to the tree in Fig. 3 by assuming that mtDNA sequence divergence accumulates at a constant rate in humans. One way of estimating this rate is to consider the extent of differentiation within clusters specific to New Guinea (Table 2; see also refs 23 and 30), Australia 30 and the New World 31 . People colonised these regions relatively recently: a minimum of 30,000 years ago for New Guinea 32, 40,000 years ago for Australia 33, and 12,000 years ago for the New World 34 . These times enable us to calculate that the mean rate of mtDNA divergence within humans lies between two and four percent per million years; a detailed account of this calculation appears

  Here's a link to the paper itself on the web with Table 2

  http://www.artsci.wustl.edu/~landc/html/cann/

  Note that using just the colonization ages of that small group of people, would still give very similar mean rates to that one derived by calibration to the human chimp divergence. So There's another way for you that doesn't invole chimps....as far as I understand it...Please correct me if I'm wrong.

  Again please accept my apology for not carefully reading your post and addressing that valid point properly. I hope I've done so now.
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  seattleniceguy

  Midget-Sasquatch, that's fascinating! Of course, looking at the mtDNA from long-isolated groups of people such as Australian aborigines would provide another way of setting the mitochondrial clock! And if these methods were all in harmony, then it would provide a strong degree of certainty about the calibration. Now why didn't I think of that!

  SNG
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  hooberus

  If I understand this correctly, the evidence that all humans are matrilineally related to each other is identical to the evidence that humans are matrilineally related to apes; the difference is only one of degree.
  

  In other words, hooberus, if you accept that science has proven that humans have a common female ancestor, then how can you deny that humans and apes have common ancestry, when the method of proof is the same?

  I don?t think that this is necessarily the case. I believe that the genetic data has caused even most evolutionists to to accept that all humans living today can be traced back to a single individual female. However, I have never heard of any evolutionist claim that the genetic data points to all humans and chimpanzees living today being traceable to be descended from a single individual female ancestor.

  "When we sample people alive today, and examine their DNA to look for clues about their past, we are literally studying their genealogy?the history of their genes. As we have seen, people inherit their genes from their parents, so the study of genetic history is also a study of the history of the people carrying these genes. Ultimately, though, we hit a barrier when we trace back into the past beyond a few thousand generations?there is simply no more variation to tell us about these questions of very deep history. Once we reach this point, there is nothing more that human genetic variation can tell us about our ancestors. We all coalesce into a single genetic entity??Adam? in the case of the Y-chromosome, ?Eve? in the case of mt DNA ?that existed for an unknowable period of time in the past. While this entity was a real person who lived at that time?the common ancestor of everyone alive today?we can?t use genetic methods to say very much about their ancestors. We can ask questions about how Adam and Eve relate to other species (are humans more closely related, as a species, to chimpanzees or sturgeons?), but we cannot say anything about what happened to the human lineage itself prior to the coalescence point." (2002, p. 54, emp. in orig.).

  Wells, Spencer (2002), The Journey of Man: A Genetic Odyssey (Princeton, NJ: Princeton University Press).

  Quoted in: How Many Times does ?Mitochondrial Eve? have to Die? by Bert Thompson, Ph.D. and Brad Harrub, http://www.apologeticspress.org/modules.php?name=Read&cat=13&itemid=2332

  While evolutionists believe that humans and chimpanzees share common ancestry, the fact remains that is ?common ancestor? is thought (based on evolution) to be a pouluation of extinct apes that split around 4-5 mya.

  It is important to remember that Evolutionists believe that everything living today ultimately shares common ancestry (ie: humans, chimpanzees, and tomatoes). And that they (assuming evolution) believe that creatures which are more similar split more recently than creatures which are less similar.
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  Midget-Sasquatch

  Hi Hooberus

  I didn't skim through your post this time.

  We all coalesce into a single genetic entity??Adam? in the case of the Y-chromosome, ?Eve? in the case of mt DNA ?that existed for an unknowable period of time in the past. While this entity was a real person who lived at that time?the common ancestor of everyone alive today?we can?t use genetic methods to say very much about their ancestors.

  You've got it. As nicely explained elsewhere on this thread (I think it was SNG, but kudos to whoever it was), one could have found their "eve" or "adam" by sampling the populations at that time. Just like someone today may be the "adam" or "eve" of a future population.

  To get some good genetic evidence for ancestry to apes, one can run some other different analyses. Like hybridization experiments to size up homolgy/similarity (very old school) or even better I suggest reading SNG's thread on endogenous retroviruses. Then also consider human chromosome 2 and especially its composition near its center. Here's a page describing its apparently being a fusion of two ape chromosomes: http://www.evolutionpages.com/chromosome_2.htm
• 

  funkyderek

  mtDNA mutation does not occur fast enough to directly observe, even though it clearly happens.

  A large enough sample of mothers and children would allow a good estimate of the mutation rate. Most children would obviously have identical mtDNA to their mother, but a certain percentage would be slightly different. This would give a good estimate of the likelihood of an mtDNA mutation in any generation. I'm not sure how large the sample would have to be to make this worthwhile, or whether it's been done. I have a vague recollection that it was, but I haven't been able to find details.
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  hooberus

  Why I said that chimps really didn't have to do with it, is because of what I read in the following paper: Nature, 325 (1987), 31-6.

  from page 33

  Tentative time scale

  A time scale can be affixed to the tree in Fig. 3 by assuming that mtDNA sequence divergence accumulates at a constant rate in humans. One way of estimating this rate is to consider the extent of differentiation within clusters specific to New Guinea (Table 2; see also refs 23 and 30), Australia 30 and the New World 31 . People colonised these regions relatively recently: a minimum of 30,000 years ago for New Guinea 32, 40,000 years ago for Australia 33, and 12,000 years ago for the New World 34 . These times enable us to calculate that the mean rate of mtDNA divergence within humans lies between two and four percent per million years; a detailed account of this calculation appears

  Here's a link to the paper itself on the web with Table 2

  http://www.artsci.wustl.edu/~landc/html/cann/

  Note that using just the colonization ages of that small group of people, would still give very similar mean rates to that one derived by calibration to the human chimp divergence. So There's another way for you that doesn't invole chimps....as far as I understand it...Please correct me if I'm wrong.

  The above does not appear to be directly based on the assumption of evolution, however the dates used for colonization (ie: "40,000 years ago for Australia") are I suspect probably based on uniformitarian dating methods. Uniformitarian dating methods are based on the a priori assumption of a uniform (ie: no recent creation, or recent catastrophic conditions) earth history: ". . . uniformity is not a law, nor a rule established after the comparison of facts, but a methodological principal preceding the observation of facts." Albritton 1967 quoted in Studies in Flood Geology Woodmorappe1999 edition p. 203

  The problem that dates calculated based on the a priori assumption of uniformity are not empirical evidence against a non-uniformitarian historical account.
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  hooberus

  mtDNA mutation does not occur fast enough to directly observe, even though it clearly happens.

  A large enough sample of mothers and children would allow a good estimate of the mutation rate. Most children would obviously have identical mtDNA to their mother, but a certain percentage would be slightly different. This would give a good estimate of the likelihood of an mtDNA mutation in any generation. I'm not sure how large the sample would have to be to make this worthwhile, or whether it's been done. I have a vague recollection that it was, but I haven't been able to find details.

  Some recent studies done (based on the pedigree methodology) have come up with results consisitent with a much higher mtDNA mutation rate than according to evolutionary estimates: http://naturalselection.0catch.com/Files/DNA%20Mutation%20Rates.html Even a talkorigins link says:

  Nevertheless, on the face of it, there is a substantial discrepancy between the mutational or substitution rates as determined by phylogenetic analysis (comparing the mtDNA sequences of chimp and human, foe example) and pedigree analysis (data based on allelic differences between close family members).

  However, the arcticle then goes on to say:

  Others who attempted to repeat Parson's results with pedigree data were unable to do so (10) and derived a rate little different from the rate given by phylogenetic data which yields an MRCA of 150,000 years. In order to help resolve these discrepancies, all the scientists have pooled their data and the result is a mutation rate of one every 1200 years based on the pedigree data - a rate which is still faster by a factor of five than the rate given by the phylogenetic approach.

  source: http://www.evolutionpages.com/Mitochondrial%20Eve.htm
• 

  Midget-Sasquatch

  Hooberus

  You find using colonization dates (derived by archeology) less preferable than empirically observed rates? Well, I can agree with you that being able to observe it directly would be best.

  I see you've mentioned Parson's paper. Yes he did (at first) report that mutation rates in mitochondria were about 20 times higher than the currently accepted figure. That would have brought the age of the MRCA around the 6000 year mark. Understandably, creationists jumped on it. But his work involved a hypervariable region which has a higher rate of mutation than other regions of the mtDNA. Others have noted that factor, as did he.

  I'm glad you've mentioned though how some empirical work produced values that came close with the currently accepted mutation rate. I think its very interesting to see how several different methods point to a very similar answer. So you can dispute the assumptions of the divergence , or colonization dates, but those two approaches combined with empirical evidence do apparently point to one reality: we've been here longer than any Genesis literalist or creationist would like to admit.

  Even if we were to go with the rate from the pooled data (about 5 times higher - so MRCA roughly 30,000 yrs ago?) it still causes problems for those believing in the historicity of Genesis.
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  AlmostAtheist

  Hooberus, I just have to say that I find you very intellectually appealing. You believe what you believe, but I don't see you distorting all sorts of science and just making stuff up to support your beliefs. When there's something legitimate that seems to support you, you point it out. But I haven't heard any "water canopy" nonsense or "frozen mamoth" babble coming from you.

  You impress me. I don't agree with you, but I guess the important thing is that YOU don't agree with you. You allow yourself to understand and accept things that contradict what you believe. I prefer to accept beliefs only when they don't contradict other things I'm aware of, but I prefer your approach to the one I took as a JW where I had to simply dismiss as lies anything I didn't agree with.

  Dave
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  GetBusyLiving

  I think Hooberus is the most honest creationist I've ever read on this board.
  
  GBL