Hello, cousin! (re: Recent common ancestors to all living humans)

You might have misunderstood this. It is not suggesting a bottleneck at 5-7k (or anywhere). It is saying that, at 5-7k ago, I had many many many great great great .... grandmothers, so many that the chances are that you too are descended from at least one of them. No bottleneck is required.I share Jazzns skepticism with regard to relatively isolated populations such as the Australian aboriginals. But it could still be correct if there was a small amount of gene flow between them and pacific islanders.

One of us is confused. What you quote from that site seems to me to be based on a gross misunderstanding of the paper. No, that is not being claimed at all. What is claimed is that there was at least one common ancester. 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. 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)

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. 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. 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.

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.

Indeed, there is a lot of confusion there.

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?) 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.

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

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. The original 10 couples (20 people) are all MRCAs. There is no requirement that there be a unique MRCA. 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. 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.

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. 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). Only for people who misunderstand what this paper is describing. Admittedly, that might be most readers. You are still discussing this as if the paper were about genetics. It isn't. That would not be an ancestor, at least as the authors are using that term. 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. 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 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.

If you would read the paper, or even read the rest of this thread, you might recognize that the paper being discussed has nothing to do with the idea that all descended from Noah, and it provides no evidence whatsoever to support such a view.

That's the point I have been trying to make. I'm glad you finally get it. Why allow your hackles to be raised about something that is totally insignificant?To me, looking at it as a mathematician, it doesn't much matter if the MRCA is 1000 years earlier than they suggest. The interesting thing is that it is far earlier than the time of mitochondrial eve. Note that this is interesting in the sense that it is counter-intuitive. I still agree that the result is totally insignificant. This doesn't really seem to be a big problem. Unless the mating is constrained to be within a bunch of separate inbreeding groups, it will be random enough for the kind of mixing needed.Looking at the case of the Australian aboriginals, it is my understanding that they lived in relatively isolated tribes. In my opinion, they should have considered each tribe as if an island in their analysis. Within each tribal group the mating was probably random enough. But even if each tribe were considered an island, this would probably push the MRCA date back only 1000 years, and I don't see that as a big deal. The reports I hear, are that there is a lot of sleeping around that actually goes on.

Yes, I agree. I see that in the text you quoted, I said "earlier" where I meant "more recent" (in relation to mitochondrial eve). That's my reaction, too.

It is the kind of result that seems to invite misunderstanding. Maybe.My assumption is that in tribal areas (Australia, parts of Africa for example), most of the intercourse between tribes would occur after inter-tribal warfare, where the victors rape the losers and perhaps take some captive as slaves. But then they would have to do hard work. The authors were pure mathematicians, not empirical scientists.That wasn't intended as a criticism. The expertise of the authors is in mathematics, so that's where they should put their effort. By publishing the results, they make it available to researchers with different kinds of expertise. I would assume that anthropologists are best equipped to fill in some of the missing data.

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