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Author Topic:   Hello, cousin! (re: Recent common ancestors to all living humans)
pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 16 of 76 (329391)
07-06-2006 1:44 PM
Reply to: Message 15 by Jazzns
07-06-2006 1:19 PM


Re: wrong again...
Are we all just agreeing differently that the Yahoo article is a misrepresentation if not wrong all together?
Not quite - RAZD is criticizing the model itself, on multiple points claiming that it "obviously" neglects parameters that it actually includes. He does so without having examined the model.
He wrote two fairly lengthy posts, neither of which mention misrepresentation in the lay news article. (I'm not sure why you seem to be defending him; in any case, this is all getting rather off-topic).

This message is a reply to:
 Message 15 by Jazzns, posted 07-06-2006 1:19 PM Jazzns has replied

Replies to this message:
 Message 17 by Jazzns, posted 07-06-2006 1:48 PM pink sasquatch has replied

  
Jazzns
Member (Idle past 3911 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 17 of 76 (329392)
07-06-2006 1:48 PM
Reply to: Message 16 by pink sasquatch
07-06-2006 1:44 PM


Re: wrong again...
I am not sure I even am defending him. I really just want to know if my original skepticism for the article was warranted. From what I read of your post #6 it seems that it was.
Based on the information you gave it seems like the original study has some merit but when the article writers took and ran with it they did so in an invalid way. I am no expert but it seems very unlikely that the MRCA between myself and a native Australian lived anywhere within a few tens of thousands of years let alone 2-5 thousand years.

Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)

This message is a reply to:
 Message 16 by pink sasquatch, posted 07-06-2006 1:44 PM pink sasquatch has replied

Replies to this message:
 Message 18 by pink sasquatch, posted 07-06-2006 3:00 PM Jazzns has replied

  
pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 18 of 76 (329425)
07-06-2006 3:00 PM
Reply to: Message 17 by Jazzns
07-06-2006 1:48 PM


incredulity is not a criticism
I am no expert but it seems very unlikely that the MRCA between myself and a native Australian lived anywhere within a few tens of thousands of years let alone 2-5 thousand years.
It is a result that seems to clash with intuition, as does the conclusion that I'm a distant cousin to sea urchins.
One thing to think about - using a simple exponential model produces the result that the MRCA lived only 800 years ago. Their model pushes this date considerably farther back by adding many more variables.
A second thing to think about when bringing up criticisms - the authors admit that truly isolated populations are a caveat that their model doesn't include. From the News & Views piece on the report:
Jotun Hein writes:
The main weakness in the models comes from migration.As the authors point out,if one region is totally isolated (something that they do not simulate),with no migrants connecting it to other subpopulations,then the universal ancestor must logically have lived before the period of isolation began. Only after that period ends would the dates for the universal ancestor become less distant.
Another interesting point from the primary paper:
These estimates would suggest, with the exchange of just one pair of migrants per generation between large panmictic populations of realistic size, that the MRCA appears in about the year 300 bc, and all modern individuals have identical ancestors by about 3,000 bc. Such estimates are extremely tentative, and the model contains several obvious sources of error, as it was motivated more by considerations of theoretical insight and tractability than by realism. Its main message is that substantial forms of population subdivision can still be compatible with very recent common ancestors.
Even when the authors restrain their migration rates down to 0.1 individuals per generation between continents, (and only during periods when migration was approximated to have occurred historically), it only pushes back the MRCA date a couple of hundred years. In other words, drastically reducing migration rates actually doesn't change the MRCA date all that much - that could be a lacking in the model (I'm no mathematician), or it could be that any migration is sufficient to allow the sort of interrelatedness the model suggests.
Maybe the model is essentially correct, or perhaps it is only correct for 99% of the population today due to pockets of isolated populations. It is important to consider the model and its implications, rather than just disregard it based on little more than incredulity.

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 Message 17 by Jazzns, posted 07-06-2006 1:48 PM Jazzns has replied

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 Message 19 by Jazzns, posted 07-06-2006 4:14 PM pink sasquatch has replied

  
Jazzns
Member (Idle past 3911 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 19 of 76 (329433)
07-06-2006 4:14 PM
Reply to: Message 18 by pink sasquatch
07-06-2006 3:00 PM


Re: incredulity is not a criticism
That is why I phrased my skepticism tentativly. Thanks for the info by the way.
I have a couple questions that you may or may not be able to answer. When using the measure of migration (.1 individuals per generation) is that applied to every possible combination of groups or just the ones that are geographically adjacent?
How do they go about determining that value? Again, with much tentative skepticism, it seems that in a number of occasions of significance .1 would be drastically large. This would be especially true if the answer to my first question is that the rate is calculated between all permutations of the groups. Since I am not a scholar on this topic I wouldn't know one way or the other. I am only asking the question based on my intuition.
One last thing, is there any consideration in the model to account for how much of the migratory input from one group to another would be stemmed by the loss of a line with a migratory ancestor at the root? In other words, is the effect of the migration permanent once it is introduced? That may not even make any sense given the details of the model but it is a thought that crossed my mind while thinking of applying migratory rates to the basic exponential model.

Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)

This message is a reply to:
 Message 18 by pink sasquatch, posted 07-06-2006 3:00 PM pink sasquatch has replied

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pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 20 of 76 (329446)
07-06-2006 5:10 PM
Reply to: Message 19 by Jazzns
07-06-2006 4:14 PM


some model details
When using the measure of migration (.1 individuals per generation) is that applied to every possible combination of groups or just the ones that are geographically adjacent?
First, to clarify, the 0.1 value was not some sort of uniform value applied to all groups, it was a specific value applied to a specific transcontinental port during a specific historical period (again, the model is attempting to take quite a bit of complex movement into account).
The model itself isn't uniform - they've run the model many times, changing many of the variables. Running the model repetitively with the same variables does not always give the same result. Assuming that 5% of people migrate from their town gives a result of MRCA at ~1400 BC. They call the 5% rate conservative, but I have no clue how accurate that statement is.
The authors try to model population structure in a simple way by designating towns, countries, and continents as geographical units. It does not appear that they make these units entirely uniform (in other words, different continents have a different town number/distribution). Some intercontinental and intercountry travel requires the use of specific "ports".
They don't use a simple distance radius model, but rather consider each town a node connected in a network to (all?) other nodes by a travel path. They do assume that migration is more likely to take place across short distances than long, so someone who migrates is more likely to do so to an adjacent town then one a few countries (or continent) away.
Possible migrations (especially intercontinental ones) are historically limited by time. Rare migration is permitted across the Bering Strait starting at 12,000 BC, but rare migration across the Atlantic to North America is not permitted until 1,000 AD, as an example.
Populations fluctuate in a historical context as well (as an example, they take into account drastic decreases in Native American populations as European populations increased there).
The model also takes into account lifespan, as well as the number of offspring per individual (there is even a compensatory value for multiple parental partners).
Hopefully that helps a bit in clearing up the level of the complexity that the model attempts to encompass.
How do they go about determining that value?
The all-important question. The model covers all these variables, but with what accuracy do they make their assumptions...
The paper is accompanied by two supplemental appendices which are each bigger than the original paper, and could potentially be papers in their own right. One of these focuses on the basis of all the assumptions listed above, with references to historical literature. (I don't feel I'm in a position to evaluate it all).
One last thing, is there any consideration in the model to account for how much of the migratory input from one group to another would be stemmed by the loss of a line with a migratory ancestor at the root? In other words, is the effect of the migration permanent once it is introduced?
Not entirely clear on your question. Let me know if the details I listed above help clear up the issue for you on this one.
One thing I found interesting, from the original paper:
Interestingly, the MRCAs are nearly always found in eastern Asia. This is due to the proximity of this region to both Eurasia and either the remote Pacific islands or the Americas, allowing the MRCA's descendants to reach a few major world regions in a relatively short time.
This is the same result, I believe, that was found using a genetic model following the distribution of Y chromosome genotypes.
with much tentative skepticism
As you should approach any scientific paper or new model. Sorry if I was a bit testy earlier - it is frustrating to see work discredited without actual examination of the work. (Not saying you were the culprit...)

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RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 21 of 76 (329739)
07-08-2006 12:16 AM
Reply to: Message 12 by pink sasquatch
07-06-2006 11:00 AM


It just doesn't add up pink.
You would see that correction if you read the paper.
Is it on line anywhere? As you pointed out the Nature article requires a login - with full rights (I only have a guest account).
Pedigrees for all humanity | Nature
I've looked, and it seems all I can find are links to the Nature article with additional "abstracts" that don't add much information.
http://www.tiem.utk.edu/~gross/math151fall05/references.html
This paper uses a mathematical model and a simulation model to estimate how many generations in the past you would have to go to find an individual who was an ancestor to all human beings currently alive (the most recent common ancestor - MRCA). They compare results from a simple model that assumes random mating between all humans to a model that assumes the world is broken down into sub-regions with transfers of humans regularly occuring between these regions, in the same way a transfer matrix describes the movement of something between various components. Their results indicate that the MRCA lived in the relatively recent past (a few thousand years ago), and going back a few thousand more years (to about 7,000 years ago) we would get to the IA point where each present-day human has exactly the same set of ancestors.
It also does not surprise me that we already have a couple creaionist references to the paper (expect more eh?):
http://www.ldolphin.org/popul.html
In one set of estimates based on this model, the mean time back to the universal ancestor is 2,300 years (76 generations, assuming a generation time of a bit less than 30 years) and to the identical ancestors it is 5,000 years (169 generations) " the time of Aristotle and the first pyramids, respectively. The latter date is especially startling: had you entered any village on Earth in around 3,000 BC, the first person you would have met would probably have been your ancestor!
That looks suspiciously like the 'news' article ...
Page not found | Creation Safaris
Notice the model converges on a few thousand years ago, not millions. Such a date is closer to Noah than Lucy. Care should be exercised interpreting what this means, because it is somewhat of a counterintuitive artifact of a mathematical model that makes certain assumptions. Another counterintuitive result, Hein claims, is that "not many generations ago (about six), members of our pedigree existed that did not contribute to us genetically." The authors are not claiming that humankind popped into existence a few thousand years ago, but only that everyone alive today had the same ancestors. ... One question he asks is, "In the idealized models, how far back would one have to go to find a single couple who are the lone ancestors of everybody?" to which we might add, "and did their names start with A and E?"
We can’t judge how valid is Professor Rohdes’ computer model, but it is interesting that this was not published by Answers in Genesis, but by Nature and by researchers from MIT and Yale - not institutions particularly interested in validating Biblical chronology. It calls into question evolutionary assumptions about human pedigrees stretching back tens of thousands and hundreds of thousands of years. It also means that all those “racial” differences between people are superficial and must be of recent origin. Like AIG has emphasized in its Biblical creationist answer to racism, we truly are of "one blood," just as Paul told the Greek philosophers on Mars Hill (Acts 17).
Not too bad a take on their part (aside from the rather obvious inferences).
But this is exactly what my objections are about: the results do not correlate with evidence from other sources.
We have evidence from genetics where they in fact LOOKED for a common ancestor in female mtDNA and male yDNA and the results were on the order of 160,000 to 200,000 years. Either the model is flat out wrong or these several teams of geneticists working in different labs with different bits of evidence (male vs female), and all the groups that have replicated those results, were all in error in the same mysterious way. (let's see ... one suspect mathematical model wrong or lots of evidence wrong ... hmmmm ... hard to decide )
We also have evidence of cultural artifacts that such migrants would carry and which are used to judge how much "international" commerce was going on at any one time (like roman coins in England before the roman invasion). These (amazingly) do not show a mixture of artifacts from around the world at some 5000 years ago. They do not even show a small subset of universally common artifacts that could be attributed to a common "MCRA" propogating population infiltrating all other populations. I think I can safely say that there are NO artifacts from africa or europe in south america at cultural ages of 5000 years ago and vice versa.
The model takes this into account - no migration until it starts at a very low rate from Europe to North America via Iceland/Greenland in 1000 AD.
Migration across the Bering Strait region begins at 12000 BC in the model.
Some anthropologists argue even earlier dates for first colonizing the americas, based on some archaeological evidence in SA.
Indiana University Bloomington
http://www.embamex.co.uk/Update/2003/05/page_06.htm
http://allendale-expedition.net/pressreleases/1117pr.html
The first blush model had the "MCRA" some 800 years ago ... his name would have to be Cassanova eh? And it couldn't be a woman that recently ... the second model -- with "more realistic" factors -- pushes that to 5000 years: wow eh?
But 10 is also a "more realistic" approximation of a million than 1, and yet it is still totally inadequate as a real approximation. Going from 800 to 5000 is a small step towards 160,000 or 200,000 years.
I would be more than unimpressed if they set the parameters and the results were more in line with those 1000 AD and 12000 BC dates ... and maybe even (possibly) impressed if they ended up with a MCRA on the order of 160,000 to 200,000 years (to match the genetic evidence).
This is where I have trouble with the historical evidence they've used -- none of it appears to have been used to ground truth {ie - TEST} the model.
Of course this critical element could also be missing from the abstracts and tidbits available, but I don't see any reference in any of the available abstracts, news items and creationist papers to this kind of model checking.
One rather obvious benchmark would be just what the factors would need to be to result in a MCRA in agreement with genetics -- then they can argue how realistic those are compared to others. I don't see any references to this being done.
And this is still not addressing the problems with the "MCRA" concept noted in Message 11
Now I don't have any problem with grouping populations into regional groups that necessarily interact and are the source populations for the ancestors of the current populations -- this is all that is necessary to make the expotential growth of possible ancestors an erroneous concept.
Nor do I have a problem with super groups of regional populations interacting at a more casual rate.
But I still don't see how this gets to shared common ancestors the way the (available documents) claim. That just doesn't follow from the premises as presented. This alone makes the claim suspect.
You would see that correction if you read the paper.
I certainly don't see it in the results presented. The abstract must be lousy. What was used to ground truth the model? A mathematical model is only as good as the information used to tune it.
Read the paper before you criticize.
I can only read what is available to me. What I see so far -- from all the information available on line and from what you have portioned out -- leaves me underimpressed.
Enjoy.

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This message is a reply to:
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Replies to this message:
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 Message 24 by nwr, posted 07-08-2006 1:12 AM RAZD has replied

  
NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 22 of 76 (329741)
07-08-2006 12:28 AM
Reply to: Message 21 by RAZD
07-08-2006 12:16 AM


Did or could have
I, also haven't read the orginal paper but I think that I understand roughly what was done.
I think they have shown that an individual in the not too distant past could have been a common ancestor to all of us. That does not say that is what did happen.
The model is then tested against real evidence and, as RASD notes, seems to be found wanting.
I'm not sure how this model could conclude that even if one person could be an ancestor that, in fact, many people were also common ancestors to us all.
I recall from the radio about a decade ago someone modeling populations who concludes that anyone born in Britain would, going back about 600 years, be related to about 80% of todays population. IIRC his model also concluded that going back further did very little to that 80%. There are always people around with whom you do not share ancestors in his model.

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anglagard
Member (Idle past 836 days)
Posts: 2339
From: Socorro, New Mexico USA
Joined: 03-18-2006


Message 23 of 76 (329743)
07-08-2006 12:39 AM
Reply to: Message 21 by RAZD
07-08-2006 12:16 AM


Re: It just doesn't add up pink.
quote:
I've looked, and it seems all I can find are links to the Nature article with additional "abstracts" that don't add much information.
Sheesh RAZD, it's Nature. Don't they have any college libraries anywhere near the other end of the sidewalk?
ABE - If you, NosyNed and anyone else wants the full text, send your email address to the account listed in my profile and I'll send it. It's only 4 pages.
Edited by anglagard, : not all librarians are scary monsters

This message is a reply to:
 Message 21 by RAZD, posted 07-08-2006 12:16 AM RAZD has replied

Replies to this message:
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nwr
Member
Posts: 6408
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.1


Message 24 of 76 (329750)
07-08-2006 1:12 AM
Reply to: Message 21 by RAZD
07-08-2006 12:16 AM


Re: It just doesn't add up pink.
Page not found | Creation Safaris
Not too bad a take on their part (aside from the rather obvious inferences).
One of us is confused. What you quote from that site seems to me to be based on a gross misunderstanding of the paper.
The authors are not claiming that humankind popped into existence a few thousand years ago, but only that everyone alive today had the same ancestors.
No, that is not being claimed at all. What is claimed is that there was at least one common ancester.
One question he asks is, "In the idealized models, how far back would one have to go to find a single couple who are the lone ancestors of everybody?" to which we might add, "and did their names start with A and E?"
Not having the paper in front of me, I cannot tell if that question was asked. However, it is clear that the study could not throw any light whatsoever on that particular question.
We have evidence from genetics where they in fact LOOKED for a common ancestor in female mtDNA and male yDNA and the results were on the order of 160,000 to 200,000 years.
I'm not sure of the relevance of this. There could be an MRCA from 7000 years ago, yet it might be that none of my genes are inherited via that chain. My DNA might all (apart from recent mutations) come from the many other ancestors I happened to have at that same era.
Edited by nwr, : fix typo (MRCA, not MCRA)

This message is a reply to:
 Message 21 by RAZD, posted 07-08-2006 12:16 AM RAZD has replied

Replies to this message:
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RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 25 of 76 (329828)
07-08-2006 10:17 AM
Reply to: Message 24 by nwr
07-08-2006 1:12 AM


The authors are not claiming that humankind popped into existence a few thousand years ago, but only that everyone alive today had the same ancestors.
No, that is not being claimed at all. What is claimed is that there was at least one common ancester.
From one of the "abstracts"
... and going back a few thousand more years (to about 7,000 years ago) we would get to the IA point where each present-day human has exactly the same set of ancestors.
That is one of the claims. One, btw, more credible than the MCRA conclusion.
Not having the paper in front of me, I cannot tell if that question was asked.
Looks like anglagard is going to get some email.
There could be an MRCA from 7000 years ago, yet it might be that none of my genes are inherited via that chain.
I'm pretty sure that contradicts the concept of "Most Recent Common Ancestor" - but then I think the concept is bogus, that it is never a single organism, but a population of a species that all contribute.

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Replies to this message:
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 Message 29 by pink sasquatch, posted 07-08-2006 11:31 AM RAZD has replied

  
RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 26 of 76 (329829)
07-08-2006 10:20 AM
Reply to: Message 23 by anglagard
07-08-2006 12:39 AM


email for paper
thanks.

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


Message 27 of 76 (329836)
07-08-2006 11:03 AM
Reply to: Message 25 by RAZD
07-08-2006 10:17 AM


From one of the "abstracts"
... and going back a few thousand more years (to about 7,000 years ago) we would get to the IA point where each present-day human has exactly the same set of ancestors.
At least that makes it clear that you have to go back a few thousand years earlier than the MRCA to find a time where all had the same ancestors. The text I commented on omitted that detail of having to look further back.
One, btw, more credible than the MCRA conclusion.
I'm not sure why you are having problems with the MRCA conclusion. If there were common ancestors at one time, then there was a most recent common ancestor.
There could be an MRCA from 7000 years ago, yet it might be that none of my genes are inherited via that chain.
I'm pretty sure that contradicts the concept of "Most Recent Common Ancestor"
From an ancestor at, say, 200 generations ago, I could expect to inherit around 2-200 of my genes. That is far less than 1 gene. Where do you see a contradiction?
Some of my ancestors from 200 generations ago likely appear multiple times in my ancestral tree. That would increase the expected amount of DNA I would inherit from them. However, the MRCA probably appears relatively few times in my ancestral tree.

This message is a reply to:
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Replies to this message:
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anglagard
Member (Idle past 836 days)
Posts: 2339
From: Socorro, New Mexico USA
Joined: 03-18-2006


Message 28 of 76 (329838)
07-08-2006 11:08 AM
Reply to: Message 26 by RAZD
07-08-2006 10:20 AM


Appendicies for Paper
Here are links for the supplemental appendicies for the Nature paper.
http://www.nature.com/...431/n7008/extref/nature02842-s1.pdf
http://www.nature.com/...431/n7008/extref/nature02842-s2.pdf
Should be lots of fodder for those who want to discuss methodology.

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pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 29 of 76 (329843)
07-08-2006 11:31 AM
Reply to: Message 25 by RAZD
07-08-2006 10:17 AM


genealogical, not genetic
There could be an MRCA from 7000 years ago, yet it might be that none of my genes are inherited via that chain.
I'm pretty sure that contradicts the concept of "Most Recent Common Ancestor" - but then I think the concept is bogus, that it is never a single organism, but a population of a species that all contribute.
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.
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?
Could one-hundred individuals have a single ancestor in common? (In other words, where and why does a limit come in to play?)
I'm short on time right now, but I'll try to respond to your longer post above - I also want to give you time to go over the paper, since it looked like you were still arguing against some incorrect assumptions in that post.

This message is a reply to:
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RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 30 of 76 (329852)
07-08-2006 11:58 AM
Reply to: Message 27 by nwr
07-08-2006 11:03 AM


I'm not sure why you are having problems with the MRCA conclusion. If there were common ancestors at one time, then there was a most recent common ancestor.
From an ancestor at, say, 200 generations ago, I could expect to inherit around 2-200 of my genes. That is far less than 1 gene.
I think you answered it. The fact is what you have is a mixture of all your ancestor genetics (plus mutations), but no one individual in a dominant source.
Some of my ancestors from 200 generations ago likely appear multiple times in my ancestral tree. That would increase the expected amount of DNA I would inherit from them. However, the MRCA probably appears relatively few times in my ancestral tree.
How do you know that all the "MRCA" genes come from one person? Put your answers together and you will end up with an MRCP (to use pinks acronym) without needing an MCRA concept. Sexual individuals do not breed alone.

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