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Author Topic:   Hello, cousin! (re: Recent common ancestors to all living humans)
RAZD
Member (Idle past 1405 days)
Posts: 20714
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Message 31 of 76 (329855)
07-08-2006 12:02 PM
Reply to: Message 28 by anglagard
07-08-2006 11:08 AM


Re: Appendicies for Paper
thanks -- I now have my evening reading....

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nwr
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Posts: 6408
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.1


Message 32 of 76 (329862)
07-08-2006 12:26 PM
Reply to: Message 30 by RAZD
07-08-2006 11:58 AM


How do you know that all the "MRCA" genes come from one person?
The term "MRCA genes" seems confused. As the subtitle of Message 29 says, this has to do with genealogy rather than genetics.
The claim the authors make in the paper we are discussing, is actually a very weak claim (though still counter-intuitive). You are mostly arguing against something stronger which is not being what is being claimed. Or, at least it is not what the original authors are claiming - maybe it is what some creationists are claiming.

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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 33 of 76 (329865)
07-08-2006 12:39 PM
Reply to: Message 29 by pink sasquatch
07-08-2006 11:31 AM


Re: genealogical, not genetic
An important point: The paper is solely modeling the genealogical MRCA, not a genetic MRCA. An ancestor in your genealogy need not contribute any genetic information to you as an individual, yet they were still in your family tree.
That's a different definition of MRCA than is used in genetics. Maybe we should call it most recent individual whose descendants have shaken hands with some ancestor or other of all other individuals. The 6 degrees of freedom thing.
You mention that you believe an MRCP (population) could exist, but not an MRCA. How small could an MRCP be for you to find it acceptable? Say, one-hundred individuals?
We are (were) talking about a time when the earth is covered with humans but even when we go back to the "founding" of species Homo sapiens there was a population that contributed to the next generation. These populations were always being mixed and remixed by sexual reproduction.
Could one-hundred individuals have a single ancestor in common?
They could have 100 individuals in common in different degrees in different (current) individuals.
Evaluating {most recent common ancestor}ship with my brothers and I get both my mother and my father - that is the closest you get to a single individual. When I include my cousins in the mix then I have also added a lot of ancestors, and this happens until the {ancestor population} starts to overlap. The overlap will be in different areas and in different degrees in different (current) individuals.
It is not a tree so much as a tapestry of interwoven threads. Some new threads are intorduced by mutations or migrants, and some are removed by death or infertility, but the number of interacting threads remains roughly the same. There never is a single parent of the group. This is what I was talking about above with a population in stasis where at any time you can measure the MRCP and come up with the same time difference for every generation.
The population evolves not the individual. The ancestors of Homo sapiens would appear no different to the first Homo sapiens than they do to us.
I see this paper has made it into the Wikipedia article
Most recent common ancestor - Wikipedia
And I find it disturbing how this is presented as an actual reality rather than a mathematical possibility, and in spite of the male\female evidence they cite that refutes it.
I'll read the paper tonight (I got it in email), and the appendices posted by anglagard, but I don't hold out much hope for it.

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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 34 of 76 (329866)
07-08-2006 12:41 PM
Reply to: Message 32 by nwr
07-08-2006 12:26 PM


see the wikipedia article for even more confusion of gene\geneology.

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nwr
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Posts: 6408
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.1


Message 35 of 76 (329869)
07-08-2006 1:07 PM
Reply to: Message 34 by RAZD
07-08-2006 12:41 PM


Indeed, there is a lot of confusion there.

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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 36 of 76 (329943)
07-08-2006 8:39 PM
Reply to: Message 29 by pink sasquatch
07-08-2006 11:31 AM


Got the paper, but ...
Okay. Right at the start I have problems with the paper.
Just past the abstract it says:
In investigations of the common ancestors of all living humans, much attention has focused on descent through either exclusively maternal or exclusively paternal lines, as occurs with mitochondrial DNA and most of the Y chromosome4,5. But according to the more common genealogical usage of the term ”ancestor’, ancestry encompasses all lines of descent through both males and females, so that the ancestors of an individual include all of that person’s parents, grandparents, and so on.
For a population of size n, assuming random mating (and so ignoring population substructure), probabilistic analysis2 has proved that the number of generations back to the MRCA, Tn, has a distribution that is sharply concentrated around log2n. We express this using the notation Tn ~ log2n, meaning that the quotient Tn/llog2n converges in probability to 1 as n approaches infinity. In contrast, the mean time to the MRCA along exclusively matrilineal or patrilineal lines is approximately n generations6, and the distribution is not sharply concentrated. For example, in a panmictic population of one million people, the genealogical MRCA would have lived about 20 generations ago, or around the year AD 1400, assuming a generation time of 30 years. The MRCA along exclusively maternal lines would have lived something like 50,000 times earlier”in the order of one million generations ago.
(Source: NATURE | VOL 431 | 30 SEPTEMBER 2004 |http://www.nature.com/nature, "Modelling the recent common ancestry of all living humans" by Douglas L. T. Rohde, Steve Olson & Joseph T. Chang - pdf document)
First off lets take the age of that "MRCA along exclusively maternal lines" and see what we get:
2004 (time of article) - 1400 AD = 600 years in round numbers.
600 x 50,000 = 30,000,000 ... 30 million years ago?
That's several times the age of the earliest hominids to say nothing of the age of Homo sapiens (~160,000 years), so there is obviously something wrong with this calculation. {abe}Re comparison to genetic MRCAs {/abe}
Putting aside the issue I have with the "MRCA" concept, the other issue I have here at the start is the "probabilistic analysis2 has proved that the number of generations back to the MRCA, Tn, has a distribution that is sharply concentrated around log2n" while stating that "the mean time to the MRCA along exclusively matrilineal or patrilineal lines is approximately n generations6" with the result of a MRCA younger that either exclusively matrilineal or patrilineal line MRCA. Let me explain:
In the male part of the population the MRCA can be either male or female.
If male, then the MRCA cannot be younger than the exclusively patrilineal line MRCA.
If female, then the MRCA cannot be younger than the MRCA for the female part of the population (it could be older).
In the female part of the population the MRCA can be either male or female.
If female, then the MRCA cannot be younger than the exclusively matrilineal line MRCA.
If male, then the MRCA cannot be younger than the MRCA for the male part of the population (it could be older).
The youngest possible "MRCA" can not logically be younger than the younger of either exclusively matrilineal or patrilineal line MRCAs, and is most likely older (th best you can say is that it is somewhere between the two exclusive line MRCAs).
If this math generates a younger MRCA for a combined population than for an exclusive line, there is obviously something wrong with this math.
If the math model used here, inside each node or whatever, includes this erroneous math to calculate "when" the theoretical possible "MRCA" occured then it must also be in error.
Gravely.
Now the issue of modelling the migration patterns may or may not be accurate (and I still have some problems there), but the conclusions re "MCRA" are -- imh(ysa)o -- invalidated.
{abe}(see post 39 - I still have problems with taking Tn=log2n as fact rather than a possible lower bound){/abe}
Enjoy.
Edited by RAZD, : formating
Edited by RAZD, : strike out section

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nwr
Member
Posts: 6408
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.1


Message 37 of 76 (329956)
07-08-2006 9:09 PM
Reply to: Message 36 by RAZD
07-08-2006 8:39 PM


Re: Got the paper, but ...
First off lets take the age of that "MRCA along exclusively maternal lines" and see what we get:
2004 (time of article) - 1400 AD = 600 years in round numbers.
600 x 50,000 = 30,000,000 ... 30 million years ago?
That's several times the age of the earliest hominids to say nothing of the age of Homo sapiens (~160,000 years), so there is obviously something wrong with this calculation.
It's not all that obvious that it is wrong. It seems possible that the earliest common ancestor along female lines need not be a hominid. (Or don't you believe in evolution?)
In the male part of the population the MRCA can be either male or female.
If male, then the MRCA cannot be younger than the exclusively patrilineal line MRCA.
Would you care to explain that one? It seems obviously wrong.
Maybe somebody raped your mother. And maybe the same person raped my mother. In that case, the two of us could have a male MRCA (namely, that rapist) only two generations back. But to find a common patrilineal MRCA would likely take many more generations. The rapist wouldn't count, since the line of descent went through our mothers so was not patrilineal.

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nwr
Member
Posts: 6408
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.1


Message 38 of 76 (329969)
07-08-2006 9:39 PM
Reply to: Message 37 by nwr
07-08-2006 9:09 PM


Re: Got the paper, but ...
Oops, I got that counter example (last paragraph) wrong. For it to work, he has to have raped both of our maternal grandmothers.

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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 39 of 76 (330010)
07-09-2006 1:00 AM
Reply to: Message 38 by nwr
07-08-2006 9:39 PM


How many generations?
It's not all that obvious that it is wrong. It seems possible that the earliest common ancestor along female lines need not be a hominid. (Or don't you believe in evolution?)
Sorry, to clarify: in comparison to the mtDNA "MRCA" (150,000 years ago) it is obviously wrong.
Of course there were more ancient ancestors.
Would you care to explain that one? It seems obviously wrong.
msg38 writes:
For it to work, he has to have raped both of our maternal grandmothers.
The rapist wouldn't count, since the line of descent went through our mothers so was not patrilineal.
Yes, I''ve reconsidered that. Thanks.
I still have trouble with the MRCA concept necessarily occurring before the "IA" point:
Take say 10 couples that are arranged in a theoretical virtual circle, male\female\male\female\etc.
Each couple has a boy and a girl child that then mate with the children of adjacent couples, boys mate to the right and girls mate to the left.
Keep going until offspring of one couple meet at the far side of the circle and mate:

M--F M--F M--F M--F M--F M--F M--F M--F M--F M--F (0)
/\ /\ /\ /\ /\ /\ /\ /\ /\ /\
-F M--F M--F M--F M--F M--F M--F M--F M--F M--F M- (1)
\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /
M--F M--F M--F M--F M--F M--F M--F M--F M--F M--F (2)
/\ /\ /\ /\ /\ /\ /\ /\ /\ /\
-F M--F M--F M--F M--F M--F M--F M--F M--F M--F M- (3)
\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /
M--F M--F M--F M--F M--F M--F M--F M--F M--F M--F (4)
/\ /\ /\ /\ /\ /\ /\ /\ /\ /\
-F M--F M--F M--F M--F M--F M--F M--F M--F M--F M- (5)
\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /
M--F M--F M--F M--F M--F M--F M--F M--F M--F M--F (6)
/\ /\ /\ /\ /\ /\ /\ /\ /\ /\
-F M--F M--F M--F M--F M--F M--F M--F M--F M--F M- (7)
\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /
M--F M--F M--F M--F M--F M--F M--F M--F M--F M--F (8)
/\ /\ /\ /\ /\ /\ /\ /\ /\ /\
-F M--F M--F M--F M--F M--F M--F M--F M--F M--F M- (9)
\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /
M--F M--F M--F M--F M--F M--F M--F M--F M--F M--F (10)
(in this diagram each line is a circle so one end connects to the other end - think of it as rolled into a cylinder)
Every child in the final circle (#10) is now related to each of the original couples at the same time and to the same degree -- who was the "MRCA" in this setup?
Notice that this occurs at (n/2) generations, and that there is no MRCA Tn at log2n = 2.3 4.3 generations as the model used projects. {edited calculation}
Now this is idealized and limited, but it probably represents more mixing of genes than occurs on an average basis for a generalized population group. There is no reason there could not be several embedded (heh) cylinders of ancestry, especially when you consider different "classes" of individuals within a society where there are some breeding taboos.
Continue the pattern and each child is always related to the full circle of individuals 10 generations ago (and consider that each generation also introduces new mutations that take another 10 generations to share). Genetic drift will mean an introduction of new material into the mix at each generation, material that will not be carried by children of the immediate ancestors to the ones carrying the mutations. Lineages will be changing during the course of this interaction:
Each male will track his yDNA back to his original male parent in the circle, with each male tracking to a different male in the original circle (while showing genetic drift through mutations that have been introduced), and while sharing the original female partners genes (also showing genetic drift through mutations that have been introduced).
Each female will track her mtDNA back to the original female parent in the circle, with each female tracking to a different female in the original circle (while showing genetic drift through mutations that have been introduced), and while sharing all the original male partners genes (also showing genetic drift through mutations that have been introduced).
Using those mutations and the (current) rate of change to then project a genetic MRCA is obviously (to me) rather bogus - it will be confusing starting differences with mutation differences.
It's more of a tapestry weaving than a tree lineage in any reproductively interacting population.
I'm not sure where this leaves me with the migration issue, but the calculation of MRCA is still suspect as noted above. Using their the number generations (assuming the migration model is valid) = 76 generations and converting by the differences noted above and you get a value of e^76/2 = 5x10^32 generations to a "MRCP" .... at 30 years per generation, I'm willing to let the real answer be somewhere in between their low number and my high number.
{abe}
Now consider that social conventions and taboos act as a control on random mating to a certain level. If we assume this to holds for only 4 generations then the MCRA 'advances' 4/2=2 generations during those periods. If we then consider that the Tn=log2n formula applies to the {four generations} as a base unit this multiplies their Tn result by 4 to arrive at a time when this theoretical MCRA occurred. Combining these you get MCRA*4/2 - or a doubling of the theoretical timing.
The curious thing is that it doesn't matter how many generations you take this non-random control over, the date is doubled -- or am I missing something? It seems to me that this should affect the expotential function ...{abe}
Latter ...
Edited by RAZD, : mcra mrca ...
Edited by RAZD, : added info at end
Edited by RAZD, : corrected log base 2 calculation

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nwr
Member
Posts: 6408
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.1


Message 40 of 76 (330058)
07-09-2006 10:24 AM
Reply to: Message 39 by RAZD
07-09-2006 1:00 AM


Re: How many generations?
Sorry, to clarify: in comparison to the mtDNA "MRCA" (150,000 years ago) it is obviously wrong.
I wondered if that was your concern.
I haven't actually read the paper. I'm trying to manage on what I have read. Maybe I will have to read it, though I think it is unimportant enough to not warrant the time. I assume that the calculation of time to matrilineal MRCA is a crude back-of-the-envelope one, making lots of assumptions. Moreover, the mathematical notation x ~ y usually denotes asymptotic similarity where one ignores a multiplicative constant (could be a large constant). So it doesn't trouble me at all that a rough computation doesn't precisely coincide with what is observed.
Now, getting to your example with 10 couples.
Every child in the final circle (#10) is now related to each of the original couples at the same time and to the same degree -- who was the "MRCA" in this setup?
The original 10 couples (20 people) are all MRCAs. There is no requirement that there be a unique MRCA.
Notice that this occurs at (n/2) generations, and that there is no MRCA Tn at log2n = 2.3 generations as the model used projects.
Actually, no, on my reading (actually non-reading) it does not project that. The log2n is an asymptotic figure - what is approached for large n. You can't expect it to apply to small n. Moreover, the asymptotic prediction is presumably based on random mating, not the constrained mating of your example.
Using those mutations and the (current) rate of change to then project a genetic MRCA is obviously (to me) rather bogus - it will be confusing starting differences with mutation differences.
I agree that is bogus. But does the paper actually attempt that? This isn't about genetics, as has been previously said.
In the 10th generation (from your example), each person has 2 parents from generation 9, 4 ancestors from generation 8, etc. That gives 1024 ancestors from generation 0. There are only 20 people in generation 0, so some of these ancestors appear multiple times. If I have calculated this correctly, then the generation 0 person directly above in your diagram occurs 252 times among those 1024 ancesters, so 252/1024 (around 25%) of the DNA comes from the generation 0 ancestor directly above. The generation 0 person 5 couples away appears only once, so only about .1% of the DNA comes from there. The 20 MRCA are all equivalent in the sense of ancestry (that they are ancestors), but they are not equivalent in genetic contribution.
In all honesty, I think you are giving this paper far more importance than it is worth. It isn't about genetics, it is about combinatorics. It has very little relevance to evolution or biology. It is of interest only because it is counter-intuitive and perhaps somewhat amusing. But, in the big scheme of things, it doesn't matter very much. You have spent more time on it than the paper was worth. My failure to actually read the original is, in my opinion, more realistic as to its unimportance.

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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 41 of 76 (330089)
07-09-2006 1:36 PM
Reply to: Message 40 by nwr
07-09-2006 10:24 AM


Re: How many generations?
I haven't actually read the paper. I'm trying to manage on what I have read. Maybe I will have to read it, though I think it is unimportant enough to not warrant the time. I assume that the calculation of time to matrilineal MRCA is a crude back-of-the-envelope one, making lots of assumptions.
None of the math is in the {document\letter} -- we should also note that this is NOT a {presented peer reviewed paper} but a LETTER to the journal, and that there are different standards for peer review for letters compared to papers.
The math is all in the appendices that anglagard has kindly linked in Message 28.
The original 10 couples (20 people) are all MRCAs. There is no requirement that there be a unique MRCA.
Exactly. This is why I would rather talk about a MRCP as the genetics comes from the population rather than a specific individual. Using an individual in the concept makes people think there is one person who is the grand-whatever of all humans (with a typical tree type geneology image firmly in mind).
Talking about a {most recent common ancestor population} on the other hand is a much more realistic an image - and no, that population does not all have to be descendent from a single person or pair of individuals, they are descendent from their MCRP. The Homo sapiens in Ethiopia did not propogate from a singe individual Homo heidelbergensis but from a population of them. The Homo heidelbergensis did not propogate from a singe individual Homo ergaster but from a population of them. Etc. How big that population was we don't know.
To get to the point of a single individual organism you have to go back to before sexual reproduction.
The log2n is an asymptotic figure - what is approached for large n. You can't expect it to apply to small n.
It is presented in the letter as a proven mathematical fact, not as a lower limit.
Moreover, the asymptotic prediction is presumably based on random mating, not the constrained mating of your example.
No mating in sexual species is completely random. This is another problem with the concept. There are limitations in space, so even broadcast {seeds\eggs\sperm\pollen\whatever} can only randomly mate within select groups.
The constrained mating of my example is artificial -- to a point. I agree. That is why I think the reality falls somewhere in between. The question then is how to model the degree of {random\constraint} in the population.
I agree that is bogus. But does the paper actually attempt that? This isn't about genetics, as has been previously said.
Yes, they claim this is about geneology instead of genetics, so my "ancestors" include my great-aunt Matilda that died a "spinster" without having any children. But if you look at the geneology conclusions of MCRA and MCRP (= their IA concept) such a person becomes a non-player. Such a person is eliminated in the next generation from my grid as contributing to the "ancestry" of other descendents. Add a third child to any couple at any level that has no offspring and the woven tapestry closes around them without any propogation from them. Further:
an·ces·tor n.
1. A person from whom one is descended, especially if more remote than a grandparent; a forebear.
Great Aunt Matilda is not an ancestor. A relation yes, ancestor no.
If we are talking geneological ancestors we are talking genetic ancestors by definition of ancestor.
If I have calculated this correctly, then the generation 0 person directly above in your diagram occurs 252 times among those 1024 ancesters, so 252/1024 (around 25%) of the DNA comes from the generation 0 ancestor directly above. The generation 0 person 5 couples away appears only once, so only about .1% of the DNA comes from there. The 20 MRCA are all equivalent in the sense of ancestry (that they are ancestors), but they are not equivalent in genetic contribution.
I agree that it is not the same level from each couple in each descendent, but rather that the proportions in each descendent are apportioned the same from the original population.
btw you can model the distribution with the quadratic progression of (x + y)^m where m is the number of generations:
m=1 -- 1x + 1y
m=2 -- 1x^2 + 2xy + 1y^2
m=3 -- 1x^3 + 3x^2y + 3xy^2 + 1y^3
m=4 -- 1x^4 + 4x^3y + 6x^2y^2 + 4xy^3 + 1y^4
etc
And this factoring can be determined easily from this graphic where you add the factors of the previous generation:
10                     1
/ \
9 1 1
/ \ / \
8 1 2 1
/ \ / \ / \
7 1 3 3 1
/ \ / \ / \ / \
6 1 4 6 4 1
/ \ / \ / \ / \ / \
5 1 5 10 10 5 1
/ \ / \ / \ / \ / \ / \
4 1 6 15 20 15 6 1
/ \ / \ / \ / \ / \ / \ / \
3 1 7 21 35 35 21 7 1
/ \ / \ / \ / \ / \ / \ / \ / \
2 1 8 28 56 70 56 28 8 1
/ \ / \ / \ / \ / \ / \ / \ / \ / \
1 1 9 36 84 126 126 84 36 9 1
/ \ / \ / \ / \ / \ / \ / \ / \ / \ / \
0 1 10 45 120 210 252 210 120 45 10 1
Each individual in generation 10 will have different couples contributing
252/(1+10+45+120+210+252+210+120+45+10+1)
= 252/1024 (note 1024 = 210)
= 24.6%
But also note that the 1's in generation 0 are the same couple -- so those should be replaced by a single 2. Wrap the diagram on a cylinder with these 1's overlapping and you can continue this pattern for more distant contributions, adding the overlapped portions for each couple's contribution. I suspect that in another 10 generations the contributions of each couple to each descedent become equal.
What this demonstrates is the power of a population in stasis to maintain a constant genetic base (except for allowing genetic drift and gradual introduction of neutral mutations). This is an argument for stasis in a constant population.
In all honesty, I think you are giving this paper far more importance than it is worth. It isn't about genetics, it is about combinatorics. It has very little relevance to evolution or biology.
It is presented as fact, and it has infiltrated Wikipedia as such. The importance is not to the relevance of the paper but to reducing the false information being promulgated.
It also has to do with the preponderance of belief that mathematical models can 'prove' elements of reality, both in the general public and in science. All math can do is model reality, it cannot become reality, and it can only make predictions -- it cannot "prove" any theory any more than the evidence can "prove" it (which is to say it can't). And the 'proof' is in the evidence and not in the math.
Enjoy.

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nwr
Member
Posts: 6408
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.1


Message 42 of 76 (330099)
07-09-2006 2:39 PM
Reply to: Message 41 by RAZD
07-09-2006 1:36 PM


Re: How many generations?
The math is all in the appendices that anglagard has kindly linked in Message 28.
Okay, I have looked over that. I don't feel inclined to check the math in detail, since I don't think it worth the effort.
This is why I would rather talk about a MRCP as the genetics comes from the population rather than a specific individual.
That's a mistake, in my opinion. The set of MRCAs might not constitute a population, but instead are scattered among many populations. The term "population" is imprecise enough that I am not convinced MRCP is meaningful. The ancestor relation, on the other hand, is precisely defined so that MRCA is well defined (even if unimportant).
Using an individual in the concept makes people think there is one person who is the grand-whatever of all humans (with a typical tree type geneology image firmly in mind).
Only for people who misunderstand what this paper is describing. Admittedly, that might be most readers.
Talking about a {most recent common ancestor population} on the other hand is a much more realistic an image - and no, that population does not all have to be descendent from a single person or pair of individuals, they are descendent from their MCRP. The Homo sapiens in Ethiopia did not propogate from a singe individual Homo heidelbergensis but from a population of them. The Homo heidelbergensis did not propogate from a singe individual Homo ergaster but from a population of them. Etc. How big that population was we don't know.
You are still discussing this as if the paper were about genetics. It isn't.
Yes, they claim this is about geneology instead of genetics, so my "ancestors" include my great-aunt Matilda that died a "spinster" without having any children.
That would not be an ancestor, at least as the authors are using that term.
If we are talking geneological ancestors we are talking genetic ancestors by definition of ancestor.
If we are talking about genetic ancestors, we should be concerned about how much of our DNA was derived from a particular ancestor. But that genetic inheritance was never a concern of the paper. It was concerned only about the ancestral relation. Once again, it isn't about genetics, it is only about the combinatorial relationship of ancestry.
It is presented as fact, and it has infiltrated Wikipedia as such. The importance is not to the relevance of the paper but to reducing the false information being promulgated.
In my estimation, you are one of those promulgating false information by virtue of your repeated treatment of the paper as if it were about genetics.
The appropriate response of a biologist to this paper should be
Ho hum!
It also has to do with the preponderance of belief that mathematical models can 'prove' elements of reality, both in the general public and in science. All math can do is model reality, it cannot become reality, and it can only make predictions -- it cannot "prove" any theory any more than the evidence can "prove" it (which is to say it can't).
I prefer to say that the science models reality, and the math investigates the consequences of the model. In this case, the model involves the ancestral relationship, and this is pretty much straight out of biology. If you think there is a problem there, it isn't in the math. The model also involves assumption about the mixing of different populations, and I expect that is over-simplified and not completely realistic.
In any case, this paper is mostly a curiosity of little or no importance to biology.

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 Message 41 by RAZD, posted 07-09-2006 1:36 PM RAZD has replied

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 Message 48 by RAZD, posted 07-10-2006 12:03 AM nwr has seen this message but not replied

  
randman 
Suspended Member (Idle past 4899 days)
Posts: 6367
Joined: 05-26-2005


Message 43 of 76 (330104)
07-09-2006 2:57 PM
Reply to: Message 1 by subbie
07-03-2006 1:11 PM


Noah?
Noah and his family?

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 Message 1 by subbie, posted 07-03-2006 1:11 PM subbie has not replied

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 Message 45 by Wounded King, posted 07-09-2006 6:42 PM randman has replied

  
sfs
Member (Idle past 2534 days)
Posts: 464
From: Cambridge, MA USA
Joined: 08-27-2003


Message 44 of 76 (330134)
07-09-2006 5:07 PM
Reply to: Message 36 by RAZD
07-08-2006 8:39 PM


Re: Got the paper, but ...
quote:
Okay. Right at the start I have problems with the paper.
Just past the abstract it says:
In investigations of the common ancestors of all living humans, much attention has focused on descent through either exclusively maternal or exclusively paternal lines, as occurs with mitochondrial DNA and most of the Y chromosome4,5. But according to the more common genealogical usage of the term ”ancestor’, ancestry encompasses all lines of descent through both males and females, so that the ancestors of an individual include all of that person’s parents, grandparents, and so on.
For a population of size n, assuming random mating (and so ignoring population substructure), probabilistic analysis2 has proved that the number of generations back to the MRCA, Tn, has a distribution that is sharply concentrated around log2n. We express this using the notation Tn ~ log2n, meaning that the quotient Tn/llog2n converges in probability to 1 as n approaches infinity. In contrast, the mean time to the MRCA along exclusively matrilineal or patrilineal lines is approximately n generations6, and the distribution is not sharply concentrated. For example, in a panmictic population of one million people, the genealogical MRCA would have lived about 20 generations ago, or around the year AD 1400, assuming a generation time of 30 years. The MRCA along exclusively maternal lines would have lived something like 50,000 times earlier”in the order of one million generations ago.
(Source: NATURE | VOL 431 | 30 SEPTEMBER 2004 |http://www.nature.com/nature, "Modelling the recent common ancestry of all living humans" by Douglas L. T. Rohde, Steve Olson & Joseph T. Chang - pdf document)
First off lets take the age of that "MRCA along exclusively maternal lines" and see what we get:
2004 (time of article) - 1400 AD = 600 years in round numbers.
600 x 50,000 = 30,000,000 ... 30 million years ago?
That's several times the age of the earliest hominids to say nothing of the age of Homo sapiens (~160,000 years), so there is obviously something wrong with this calculation.
No, there is nothing wrong with your calculation. If humans had had a panmictic population of size 1 million for their entire history, the most recent common ancestor in the maternal line would have occurred something like 1 million generations ago(*). In the real world, however, the effective population size of humans was about 10,000, so the most recent common maternal ancestor actually lived about 100 times more recently.
(*) There is one mistake, in fact, but it's not yours: the expected time to the MRCA for purely maternal inheritance is N/2 generations, not N generation. (Also, 20-25 years is a more realistic generation time for most of this period than 30 years.)
On your other points, read nwr's responses. He or she understands the paper, and so far you don't.

This message is a reply to:
 Message 36 by RAZD, posted 07-08-2006 8:39 PM RAZD has replied

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 Message 51 by RAZD, posted 07-10-2006 12:10 AM sfs has replied

  
Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 45 of 76 (330142)
07-09-2006 6:42 PM
Reply to: Message 43 by randman
07-09-2006 2:57 PM


Re: Noah?
Well done Randman, you are now the 1 millionth creationist to make the same mistkae in terms of scientific hypotheses concerned with common ancestry within a breeding population. This group isn't Noah and his family for the same reasons that mitochondrial Eve and Y chromosome Adam didn't frolic together in the Garden of Eden.
TTFN,
WK

This message is a reply to:
 Message 43 by randman, posted 07-09-2006 2:57 PM randman has replied

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 Message 46 by randman, posted 07-09-2006 10:13 PM Wounded King has not replied

  
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