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Author Topic:   How will creationists react to the first human-chimp hybrid?
Quetzal
Member (Idle past 5872 days)
Posts: 3228
Joined: 01-09-2002


Message 78 of 138 (449818)
01-19-2008 9:02 AM
Reply to: Message 74 by johnfolton
01-18-2008 11:13 PM


Re: The myth of mitochondrial Eve
That all depends how you calibrate the mutation rates for mitochondrial dna.
No, it doesn't actually. "Mitochondrial Eve" is the result of a mathematical population genetics model called "Coalescent Theory". (You can find a reasonably clear introduction here). To grossly oversimplify, coalescence traces genetic lineages back in time from the present (unlike many pop gen models which take a present population and project changes in genetic composition into the future), to a point where different genetic lineages come together - the "coalescence", or "most recent common matrilineal ancestor". Coalescence of mtDNA lineages, operating only through the female (matrilineal) line, does NOT mean there was only one woman alive at that point. It means that all of her other female contemporaries either were also the ancestors of all modern humans (because the carried the same mutations) or left no current descendants. The coalescence of "her" (actually better said "their") mtDNA lineage comes in at around 140,000-200,000 years ago (see, for instance, Cann RL, Stoneking M and Wilson AC, 1987, "Mitochondrial DNA and human evolution", Nature 325:31-36).
The point of all this is: don't get too wrapped up in a name. Scientists can be as unfortunately whimsical in their "popularized names" as anybody else. Naming the mtDNA "most recent common matrilineal ancestor" "Eve" was simply whimsy, and not intended to be related in any way shape or form to the Biblical "Eve".

This message is a reply to:
 Message 74 by johnfolton, posted 01-18-2008 11:13 PM johnfolton has not replied

Replies to this message:
 Message 79 by NosyNed, posted 01-19-2008 11:28 AM Quetzal has replied

  
Quetzal
Member (Idle past 5872 days)
Posts: 3228
Joined: 01-09-2002


Message 80 of 138 (449846)
01-19-2008 12:31 PM
Reply to: Message 79 by NosyNed
01-19-2008 11:28 AM


Re: A question for Quetzal re Y and mtDNA lineages
Doesn't it mean that she left "no currant descendants" through an unbroken mother to daughter line? She may well have descendants alive but there may have been a generation of all males between her and us. Correto?
"Eve" is the one that did leave descendants. Her contemporaries that didn't have the particular neutral mutation patterns in their mtDNA that we see today are the ones that didn't. And yes, there could very well have been a "break" in the non-Eve lineages where only males were produced. The .pdf I referenced has a couple of nice diagrams showing how this could happen.
Is there an initial population size where, over enough time, you MUST get down to a single Y ancestor and singe mtDNA ancestor showing in the resultant population? In other words, is this result just what you would expect if the human (for example) population stays not "too" large for long enough?
Not really. I'm not expert at this (pop gen was my second worst course in school, and I have attemptd faithfully to avoid it since), but my understanding is that initial population size doesn't matter - eventually every lineage will coalesce. Remember, we're tracing polymorphisms back in time from current populations. Additionally, it doesn't matter much what the size of the sample of modern populations is - the statistical variance based on sample size, which is usually 1/n, is only 1/logn with coalescent theory (don't ask me why). So either way you look at it, population size doesn't matter.
I see this happening by pure chance as once a line happens to encounter an all male (for the mtDNA) generation it is gone and over time we would expect the number of threads of mtDNA to dwindle.
Yeah. The whole concept arose out of pop gen attempts to model random drift.
Has there been any pop. gen work on this?
Tons. Here's a good review: Rosenberg NA and Nordborg M, 2002, Geneological trees, coalescent theory, and the analysis of genetic polymorphisms, Nature Reviews 3:380-390. That review covers most of the studies up to that point (2002).

This message is a reply to:
 Message 79 by NosyNed, posted 01-19-2008 11:28 AM NosyNed has replied

Replies to this message:
 Message 81 by NosyNed, posted 01-19-2008 1:42 PM Quetzal has replied

  
Quetzal
Member (Idle past 5872 days)
Posts: 3228
Joined: 01-09-2002


Message 82 of 138 (449861)
01-19-2008 1:51 PM
Reply to: Message 81 by NosyNed
01-19-2008 1:42 PM


Re: A question for Quetzal re Y and mtDNA lineages
Are you saying "initial" == current population size doesn't matter? That makes sense to me.
When I said "initial" I meant the population at sometime in the past. Specifically the time of mtDNA Eve or Y Adam. Does that also not matter? It seems to me that it must matter. At least if it was larger then I must have more time before the lineages coalesce. Obviously a population of 20 million during Roman times will not have coalesced under most circumstances by now. But a population of 1,000 may well be almost sure to have.
Yes to both. One of the sort of really counterintuitive parts of coalescent theory is that neither the initial (past) nor modern sample size matters for the calculations beyond a certain point (which I can't remember). In fact, the most recent female common ancestor of all living humans (from all genetic lineages male and female) lived around 10,000 years ago, and the most recent common ancestor period of all modern humans coalesces to around 3000 years ago. So yeah - we're all related. How's it going, cuz? Now you see why I gave up on pop gen.

This message is a reply to:
 Message 81 by NosyNed, posted 01-19-2008 1:42 PM NosyNed has not replied

  
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