On Saturday, March 11, 2023 at 7:55:41 AM UTC-8, T. Snell wrote:
On Thursday, January 12, 2017 at 1:30:49 PM UTC-6, Richard Smith wrote:
On 12/01/17 18:56, taf wrote:
On Thursday, January 12, 2017 at 10:23:35 AM UTC-8, wjhonson wrote:
If every living person were atDNA tested, would we be able to reconstruct the DNA of Charlemagne?
No.
I do not know a ton about genetics, but I believe because of the random way that
dna or segments of dna can be present in one person (sibling,cousin etc.) and not
another person even when they are closely related, and even though we only inherit
50% from each parent I think if enough of his descendants were tested it might be
possible to piece most of it together. They have come so far with dna that they were
able to estimate my y-dna haplogroup even though I havent tested.
I previously gave short answers, but here is a really long one.
'Come so far' has nothing to do with it. The problem cannot be solved by scientific progress because the problems are not related to scientific capabilities, they are statistical and demographic.
The dual problems are, first, the survival of the DNA to modern times, and second, identifying that DNA. As Denis already has described today, in a single line the amount of DNA deceases by 50% per generation, and so the chances of any descendant of
Charlemagne actually having Charlemagne's DNA is slim. However, there are probably hundreds of millions of descendants of Charlemagne, so one would think that most of the DNA should survive somewhere among this group. However, most of these are unusable -
even for a much closer relationship, you need corresponding genealogy, and most of the descendants of Charlemagne do not know and cannot be traced to him.
Even if they all had pedigrees, there is a problem that would prevent complete reconstruction of Charlemagne's DNA. Unless I am forgettign something, Charlemagne's only known descent comes via two children, Pepin and Louis. Each would have 50% of
Charlemagne's DNA, and would be predicted to share half of that - 25% of Charlemagne's DNA would be carried by both; 25% would be unique to each, adn 25% would be carried by neither - this would be lost, impossible to ever determine. Further, one of
those lines, the Italian line, has several successive generations with only one known child with descent. In each of those generations, that 25% unique to the son, Pepin in this case, would be again divided by half. While there is speculation of others,
all proven descnts from Pepin (unless there is one not coming to mind) come through Heribert I of Vermandois, so that means the 25% unique to Pepin is reduced to just over 3%. Louis doesn't have the same problem, having descent through multiple children
but there is still going to be some loss, so taken together, we have already lost half of Charlemagne's DNA before things start seriously branching, and it can never be recovered, and that's before we even start doing any actual science. With the
progressive losses of DNA over subsequent generations, the proportion of Charlemagne's DNA still around in anyone is small and many people with Charlemagne's DNA will have the exact same piece, a piece so small that it will also be shared by a much
larger cluster of descendants of some 5000 year old neolythic farmer or hunter-gathrer who had it before Charlemagne, while most Charlemagne's DNA will have been lost entirely (or may be carried by Charlemagne's descendants but not through Charmemagne's
line, instead coming a different way from that hunter-gatherer, leading us . . . ).
Now let's look at the second problem. How you go about identifying DNA from a specific ancestor over the short range is to identify and test all of the known (via standard genealogy) descendants of the target ancestor. (There is a more tedious approach
one can do next, progressively reconstructing the genomes of the intervening generations until you get back to the target and their spouse, without being able to tell which is which.) You then test known descendants of ancestors of the target and matches
between target descendants and target-ancestor descendants, to distinguish which target-descendant DNA would have come via the target. That is how you identify just a small part of the genome of the target. As pj already mentioned, we have no known
descents from Charlemagne's ancestors. Even if you accept some of the assumptions made about kinships in his tree, you would need a descendant of an ancestor of Charlemagne that you know doesn't also descend from Charlemagne, or you couldn't distinguish
whether the shared DNA came Charlemagne's lineage and not from his wife. We need someone we KNOW does not descend from Schalemagne, yet who is descended from one of his ancestors, and we can't even be sure that any given member of the European diaspora
is NOT descended from Charlemagne - indeed, statistical models predict they all are. The very pervasiveness that enables a lot of descendants to be tested deprives us of any utility of the results.
And that brings us to the other big problem. The whole process is predicated on the assumption that the people being tested are only connected via the descent of interest. Modelled on a modern diverse highly-mobile population, this is a viable assumption,
but it is an assumption. However, if they are related in any other way, then one could get a coincidental match that has nothing to do with the target line, and hence falsely identify shared DNA as belonging to the target. In the more insular and inbred
communities of the 18th century, this assumption loses all validity. Over a 1200 year time span, anyone descended from Charlemagne is also going to be descended from essentially every other identified person of the time in Europe with known descendants.
The shared DNA could come from any one of them. This also stands in the way of a more tedious generation-by-generation reconstruction, which not only requires no other shared ancestors, but they would also need only to have a single descent from the
common ancestor, Charlemagne, but everyone descended from Charlemagne once is descended from him many times over, thereby poisoning generation-by-generation reconstruction. That leaves descent from shared ancestry as the only means to identify relevant
DNA, and as already discussed, we don't have that. At this depth, we are talking about tiny pieces shared of DNA that could come from a common ancestor 1200 years ago or 12,000 years ago, with no ability to say Charlemagne is the one it came through.
As Denis pointed out, the uniparental DNA markers are easier to trace deep, but for that it absolutely requires male-line descents from multiple sons of a male target, or female-line descents from multiple daughters. We don't have that here, so it is a
dead issue.
It all just doesn't work, and no amount of scientific progress will resolve these issues, that have nothing to do with the science. The only way to identify Charlemagne's DNA would be to locate a bone from him and recover ancient DNA from it. Getting it
through genetic genealogy is a non-starter.
taf
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