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

by seattleniceguy 48 Replies latest jw friends

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  funkyderek

  seattleniceguy:

  Another superb post. Keep up the good work!

  hooberus:

  The data is actually more consitent with the concept of Biblical Eve than is often presented.

  I agree! It is completely consistent with the concept of Biblical Eve, but only if you allow an mutation rate of 25-40 times greater than what is actually observed. How would you account for such a rapid rate of evolution, hoob?
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  seattleniceguy

  Thanks, funkyderek!

  hooberus, this page describes ME and how we find her date. No mention of chimps. Chimps simply don't have anything to do with this discussion. Please read my article and sources more carefully.
  http://www.talkorigins.org/faqs/homs/mitoeve.html

  SNG
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  Euphemism

  Just to play devil's advocate here... one thing I don't see in that page is an explanation of how the rate of mutation of mitochondrial DNA is calculated; i.e. what observations/experiments is it based on?

  The only examples I found from a quick google were calibrations based on a geological dating of evolution. If that is the only source of calibration, then mitchondrial DNA, while enhancing the internal consistency of existing evolutionary dating, does not constitute independent confirmation.

  Does anyone know of any alternative sources of calibration?
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  drwtsn32

  Another excellent post, SNG. I look forward to your followup!
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  seattleniceguy

  Euph,

  I think you're right. I didn't realize the mutation rate is so low. I found this explanation (which sounds a lot like what you probably read) by Alec MacAndrew:

  The normally accepted rate is one mutation every 300 to 600 generations (6000 to 12000 years) and this is calibrated, as Wieland correctly says, by counting mutations in great ape and human mitochondria and regressing back to the age of their divergence as determined by fossils dated by radiometric dating.

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

  Since mutations occur at this low rate, it is not possible to directly observe a rate of observation. As you point out, this would make this evidence secondary (at least as far as determining a date for most recent common matrilineal ancestor). To state the problem in another way for anyone who is having trouble following along:

  • We know from direct observation that mitochondrial DNA is passed down from a mother to her children.
  • We predict from the above observation that a) closely related groups of humans will have similar or identical mtDNA, and b) disperate groups of humans will have divergent mtDNA, and c) the greater the geneological distance, the greater the divergence in mtDNA will be.
  • We know from direct observation that those predictions are true.
  • Since logic tells us that at some point in time we had a common matrilineal ancestor (for logical proof see: http://www.talkorigins.org/faqs/homs/mitoeve.html), we know that the differences in mtDNA that we see in the human population have occurred since our most recent common ancestor by matrilineal descent.
  • The question is, how often do mutations occur? Only by coming up with a rate of mutations can we get an actual date for the most recent common ancestor.
  • Since the mutation rate is too slow to be observed, it was extrapolated by the means given above.

  Actually, even disregarding the question of the convergence date, mtDNA provides us with a lot of geneological data, very similar in application to the retroviral sequences and cytochrome c sequences I posted about earlier.

  One interesting implication is shown by comparing mtDNA from humans on the different continents. In comparing a key sequence of about 900 base pairs, only 1% Europeans differed by more than 12 base pairs. The same was true in Asia. In Africa, however, 37% of people differed by more than 12 base pairs. This indicates strongly that humans have lived in Africa for the longest time, supporting the "Out Of Africa" model of human evolution.

  Actually, my main point in all of this was not to establish a date for the most recent common matrilineal ancestor, but to lay down the fundamentals of mtDNA in preparation for the next installment.

  Thanks for your astute observations!

  SNG
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  seattleniceguy

  I should apologize to hooberus for speaking too soon. You are correct in stating that the mitochondrial clock is indeed set by assuming a common ancestor between humans and apes, but that's only because:

  • mtDNA mutation does not occur fast enough to directly observe, even though it clearly happens.
  • The date for the most recent common matrilineal ancestor is not in itself meant to be evidence for anything, although it does fit with our understanding of human evolution.

  SNG
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  Euphemism

  Thanks for clarifying, seattleniceguy. You also wrote:

  Actually, even disregarding the question of the convergence date, mtDNA provides us with a lot of geneological data, very similar in application to the retroviral sequences and cytochrome c sequences I posted about earlier.

  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?
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  seattleniceguy

  Euph,

  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 tried to write the same thing in my last post, but I couldn't frame it satisfyingly so I omitted it. Thanks for putting that into the right words.

  SNG
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  Abaddon

  Mitochondrial Eve is one phrase that should not have been coined - I think whoever did has said as much. Half the problem is it isn't actually what it says it is (as there's always more than one), but "putative common female ancestor" isn't anywhere near as flashy.

  The problem that hooberus now has is a typical one for someone trying to insist on a more literal interpretation of the Genesis creation story. In seeking to assault one strand of evidence he (unknowingly?) engages another.which undermines his argument.

  This 'super-focus' is typically caused by approaching a subject with the intent of disproving it rather than understanding it and coming to a conclusion on its veracity after study. That way you focus on what seems to be a problem and don't get sight of the rather large body of interelated evidence supporting it.

  For example English spelling seems to be all wrong to a non-native learner, until you understand why it is all wrong. Most native speakers of English don't understand why it is all wrong so it is scarselt surprising non-native speakers feel that. However, when you know WHY, then English spelling is understandable.

  It is also ironic that proponents of a literalistic belief in the Genesis account constantly ask for the theory of evolution to be proved but are incapable of providing such proof of their own theory, and indeed avoid chronological contradictions they are unable to answer that unanswered make their entire claim to a recent creation (or other events described in Genesis) seem impossible.

  Nice posts SNG!
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  badboy

  aN INTERESTRING ARTICLE!