GENEALOGY-DNA-L Archives

Archiver > GENEALOGY-DNA > 2009-06 > 1244217238


From: Vladimir Voevodsky <>
Subject: Re: [DNA] revised TMRCA calcuations for the R-L21 results
Date: Fri, 5 Jun 2009 11:53:58 -0400
References: <952121.68353.qm@web81102.mail.mud.yahoo.com><BAY106-W4A9D3A136EC8B30DF0CF4BC4B0@phx.gbl>
In-Reply-To: <BAY106-W4A9D3A136EC8B30DF0CF4BC4B0@phx.gbl>


I sent it two days ago but it looks like it did not go through.


When we say that the current male-line MRCA lived 100,000 years ago
it means that
100,000 ago there lived a guy whose male line descendants travelled to
all places on earth and participated in the procreation process there
in such a way as to pass their Y chromosomes to all males of the later
generations.

Assuming that humans lived in a larger area 100,000 years ago than
200,000 and taking into account that males and male descendants in
particular have a much higher mobility rate than females and female
descendants it becomes obvious that one should expect the male MRCA to
date later than the female one.

In other words I would think that the major factor which affects the
date difference is the difference in geographical mobility between Y
chromosomes and mtDNA.

It would be much easier to find the expected answers to such questions
if there were a computer program/system on which we could run history
forward with different parameters and see to what genealogies (on the
time scale of 100,000 years if necessary) and what patterns of genetic
diversity it leads.




Vladimir.

On Jun 4, 2009, at 12:20 PM, Thomas Gull wrote:

>
> I think Ken addressed your question about why the difference would
> be that big, in a mathematical way. Another aspect might be that Y-
> DNA survives based on factors that affect only males, where mtDNA
> survives based on a much larger population pool (both males and
> females carry the mtDNA).
>
>> Date: Wed, 3 Jun 2009 21:38:41 -0700
>> From:
>> To:
>> Subject: Re: [DNA] revised TMRCA calcuations for the R-L21 results
>>
>> Never said they had to be identical or in the same generation. It
>> may have taken thousands of years before the Y and Mtdna lines
>> accumulated variance that survives until today. In relative terms
>> this is "almost" pertaining to the ages of Adam and Eve (who would
>> be older). Crawford said they expected similar ages because their
>> effective population sizes were expected to be equal.
>>
>>> It is because of the inherent randomness of some of the processes
>> (drift, bottlenecks, >sex-specific demographics, natural selection)
>> that
>> you would not expect these two >individuals to have lived at the same
>> time. That would be a phenomenally great >coincidence.
>>
>> Specifically how would you explain this big a difference between
>> TMRCA est. of 171-238Kya for the Mtdna line and the 46-109kya of
>> TMRCA of Y?
>>
>> Gary
>> Mexico DNA Project Admin.
>>
>> ______________________________________________________
>> --- On Wed, 6/3/09, Thomas Gull <> wrote:
>>
>> From: Thomas Gull <>
>> Subject: Re: [DNA] revised TMRCA calcuations for the R-L21 results
>> To: "genealogy dna" <>
>> Date: Wednesday, June 3, 2009, 5:58 AM
>>
>>
>> How would anyone explain that by total coincidence all living
>> humans were provably descended from two specific individuals who
>> lived at the same moment within the last 150,000 or so years? The
>> odds against that are astronomically large unless there would be
>> some extremely specific process that makes the two chains of event
>> work in lockstep. There isn't. I agree 100% with VV - why would
>> anyone have ever expected the Y-DNA and mtDNA trails for living
>> humans to lead back to one male and one female living in the same
>> generation? I'm sure it made headlines because of the Biblical
>> Adam and Eve concept. But that's not what we're talking about here
>> - not the "first humans" concept, but the "last winners in the
>> genetic sweepstakes" concept. And there was one "sweepstakes" for
>> males and one for females, with no scientific process that would
>> make you expect them to end up in the same timeframe statistically.
>>
>>
>> It is because of the inherent randomness of some of the processes
>> (drift, bottlenecks, sex-specific demographics, natural selection)
>> that you would not expect these two individuals to have lived at
>> the same time. That would be a phenomenally great coincidence.
>>
>>
>>> Date: Tue, 2 Jun 2009 19:26:16 -0700
>>> From:
>>> To:
>>> Subject: Re: [DNA] revised TMRCA calcuations for the R-L21 results
>>>
>>>>> TMRCA for Y and Mtdna should theoretically go back almost to
>>>>> genetic
>>>>> Adam and Eve respectively.
>>>
>>>> Sure, but the the TMRCA estimates need not be identical (or even
>>>> similar) this there is no a priori reason to presume MRCA-Y and
>>>> MRCA-
>>>> mtDNA were contemporaries of each other. That is, there is nothing
>>>> that dictates they lived in the same time or place.
>>>
>>> Not so. Crawford states this was unexpected and the news made
>>> headlines about 10 years ago. Google genetic adam and eve. He
>>> references Wilder et al 2004b when he states that it could be
>>> natural selection or sex specific demographic processes.
>>>
>>>> No. The lower effective population size (assuming that Crawford is
>>>> even right on this point) would cause the TMRCA to be lower in
>>>> reality. Lower TMRCA estimates are reflecting the reality, not a
>>>> distortion of it.
>>>
>>> How would you explain differently, genetic adam being about half
>>> the age of genetic eve when Geneticists say it is drift or sex
>>> specific demographic processes?
>>>
>>> Gary
>>> Mexico DNA Project Admin.
>>>
>>
>>
>> -------------------------------
>> To unsubscribe from the list, please send an email to
>> with the word 'unsubscribe' without the quotes in the subject and
>> the body of the message
>
> -------------------------------
> To unsubscribe from the list, please send an email to
> with the word 'unsubscribe' without the quotes in the subject and
> the body of the message

This thread: