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Mitochondrial DNA analysis is limited

politas said:
Discovering actually when a particular species' common mtDNA ancestor existed is actually a lot easier than calculating the probabilities, since that calculation is entirely based on actual observed data.
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Although this is believable to me (that calculating the probability of roughly when a species' common mtDNA ancestor existed is too complex for us to currently do in a meaningful way) it seems to be contradicted by folks who use probability calculations to assert that at a rough period of time (0 AD for example) each person alive was either the ancestor of all humans living today, or no humans living today. I understand this is not quite comparing apples to apples, but what makes probability calculations for a species' common mtDNA ancestor (or common y chromosome ancestor) signficantly more difficult than the other type calculation?
 
Dave1001 said:
Although this is believable to me (that calculating the probability of roughly when a species' common mtDNA ancestor existed is too complex for us to currently do in a meaningful way) it seems to be contradicted by folks who use probability calculations to assert that at a rough period of time (0 AD for example) each person alive was either the ancestor of all humans living today, or no humans living today. I understand this is not quite comparing apples to apples, but what makes probability calculations for a species' common mtDNA ancestor (or common y chromosome ancestor) signficantly more difficult than the other type calculation?
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I didn't say the calculation was impossible, just that I would barely know how to start doing such a thing. I would imagine part of the difference between the two exercises is that while we can discover the common mtDNA ancestor by analysing direct genetic evidence, working out how far back to go to find everyone either being an ancestor to everybody or nobody can only be done via statistical/probability analysis. Oh, and it's a lot further back than 2,000 years.
 
politas said:
I would imagine part of the difference between the two exercises is that while we can discover the common mtDNA ancestor by analysing direct genetic evidence, working out how far back to go to find everyone either being an ancestor to everybody or nobody can only be done via statistical/probability analysis.
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Well that would indicate that one's verifiable by another method and the other's not. Why might be a reason to remain skeptical about the "everybody in the world shares relatively recent common ancestors" claims.

Oh, and it's a lot further back than 2,000 years.
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That make sense as a difference between the two excercises.
 
Dave1001 said:
Well that would indicate that one's verifiable by another method and the other's not. Why might be a reason to remain skeptical about the "everybody in the world shares relatively recent common ancestors" claims.
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I'm not sure what you're saying, there. I can accept being skeptical of the "people x years ago are either ancestors of everybody, or ancestors of nobody" claim, since it is based largely on probability analysis, but "everyone shares a common mtDNA ancestor between 150k-250k years ago" is pretty hard science. There's definitely good evidence for that.

I'm not sure that 150k-250k years ago is what I'd call relatively recent, though. For reference, Homo sapiens developed around 200k-250k years ago.
 
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