If you go back just 3 generations you have 4 great grandmothers. Only one of those great grandmothers gave you your mitochondrial DNA, but all 4 potentially contributed to your genome. The same for your 4 great grandfathers and your Y chromosome, if you are a dude.
Thanks for contacting me. As I said in my post, I’m a physicist so I’m trying to understand the issues and its hard for me to discern between reasonable ideas and unreasonable ideas in the genetics/biological realm.
I do have some questions/clarifications to ask.
If the genetic mathematical models are relatively simple and may have some problems by a factor of 10 let’s say, why can’t coalescence also be a bottleneck? I will say that when I talk to biologists and geneticists about the precision of the mathematical models they seem to be very far from what we would consider viable models in physics.
I certainly understand the three possible models of Adam and will discuss the Recent Sole Genealogical Progenitor Adam in my next post.
I also think it is certainly possible that Story 2 is possible with interbreeding and that would be consistent with my post that you have linked.
Finally, is the cultural Great Leap Forward still a viable model? If so, could a physiological change precipitated that? If so, how did that change permeate to humans throughout the globe?
The main point is that a constant population can produce most recent common ancestors for mitochondrial DNA and the Y chromosome. This is because some women don’t have daughters which ends their mitochondrial lineage, and people marry their distant cousins which amplifies the mtDNA or Y chromosome of their common ancestor. It is possible that a future mtDNA Eve or Y chromosome Adam is alive today, one of billions of fellow humans. I would also suspect that we carry little, if any, DNA from mtDNA Eve or Y chromosome Adam other than our mitochondria or Y chromosome. That other DNA comes from other ancestors that were older, the same age, or younger than the common ancestors for our mtDNA and Y chromosome.
When I look at this article https://discourse.peacefulscience.org/t/heliocentric-certainty-against-a-bottleneck-of-two/61/12 it seems that just a factor of 5 would give a genetic Adam and Eve as recent as 100K years ago. The Moulon Sheep demonstrate to me that the model could be off by that much. So as a physicist, I really don’t see how geneticists make such definitive statement when the evidence seems to indicate that their models could be off by factors that would radically modify their conclusions. A simple factor of 5 easily allows a single couple at 100K.
In physics we haven’t discovered something until we demonstrate it to the 5 sigma level including statistical and systematic uncertainties. The chart shown in this article has 100 K less than 2 sigma from the mean, which in physics isn’t even considered anywhere near outside of the boundary of likely, not just viable. If you showed a physicist the chart in this article, they would say that even 0 years is a reasonable conclusion from the data.
Yes, I understand this. That doesn’t refute the possibility of a single couple though. I certainly understand that MtDNA Eve and Y chromosome Adam don’t necessarily imply a single couple. What I don’t understand is why a single couple isn’t a viable option. When I look at the statistical analysis used to try to say that isn’t a viable option, the precision quoted would be unacceptable in physics.
Regardless, the width of the distribution makes 100K easily a possibility within just 2 sigma. You haven’t addressed that. In physics 2 sigma is likely to happen. We would consider that one of the most likely outcomes, but the geneticists want to say that CAN’T happen. To a physicists such a conclusion is crazy (based on the data being presented. It is possible the correct data isn’t being presented).
I don’t want to be disrespectful and I don’t know your scientific credentials, but this statement shows the exact kind of lack of understanding of statistics that I am referring to among certain people who make claims. There is a huge difference between a 5 sigma positive signal and an exclusion. Geneticists claim a 2 person bottleneck is EXCLUDED (not a 5 sigma positive signal at all) but the data presented to me shows the “exclusion” is about 2 sigma from the mean which in physics is not an exclusion at all but is predicted to be seen.
Far as I am aware, there is not a 5 sigma signal supporting a two person bottleneck 150,000 years ago. At best, you can only say that a two person bottleneck is not ruled out, but there is no positive evidence supporting a two person bottleneck. IOW, the null hypothesis is supported, or rather a lack of statistical significance for a two person bottleneck.
“Based on all of the genetic evidence, the conclusion from science is consistent with the biblical idea that humans have descended from one male and one female, and that both lived maybe 150,000 years ago or so. Although most genetic scientists would argue that those two lived among a population of a few thousand and probably lived at different times, the scientific models on which those latter conclusions are based seem to me to be too simple without precise validation. Consequently, it seems that the current confirmed scientific evidence does indeed point to a conclusion that is in alignment with the biblical record of a historical Adam and Eve being the genetic ancestors of modern humans.”
I’m speaking to a non-technical audience in my blog. Scientific evidence that says there is a Meve and Yadam and that within very reasonable uncertainties contained in models that can be shown to have some problems certainly to me points to a conclusion that is reasonably consistent with a 2 person bottleneck. A 2 sigma consistency is very consistent in physics.
So I’m not claiming a 5 sigma supporting evidence. I’m claiming a 2 sigma consistency. Though I didn’t know it was actually 2 sigma until I got the information from this group. So I would say that the further information from this group actually supports my thesis in the blog with even more hard numbers, and I’m pretty sure those numbers don’t even include systematic uncertainties.
The evidence is also consistent with a constant population and a lack of a 2 person bottleneck. Even by your own admission, the evidence can’t distinguish between the two so you can’t claim that one conclusion is favored over the other.
It’s certainly true that genetics is modeling much more complex systems than is typical for physics, and genetics models are correspondingly less precise. Even so, your statement seems a little sweeping. QCD was considered a viable and valuable model for decades before it could be used to calculate something as basic as the mass of the proton to within an order of magnitude, wasn’t it?
You seem to have confused two different sigmas. The sigma you’re talking about is the sample standard deviation, while the relevant sigma is the standard error on the mean, which is sigma/sqrt(N), where N seems to be about 10 million. In HEP terms, it’s analogous to reconstructing 10 million decays of a broad resonance and asking how confident you are that you haven’t gotten the rest mass wrong by a factor of five. In reality, this case is a little different, since we really want to know the maximum true age of four non-coalesced lineages, since that sets a limit on when a two-person bottleneck could have occurred. As I recall, @swamidass used the median of the estimated ages, which seems a conservative choice.
Note that the model of heterozygosity in the Mouflon sheep study assumed neutral evolution, which may well be wrong in this case. By contrast, the results that @swamidass describes make no assumption about neutrality, and in fact the researchers report finding loci with both purifying and directional selection. The primary assumption in those results is that the mutation rate has been more or less constant, something that we have multiple reasons for thinking must be true.
I’m not confusing sigmas. You cannot look at just the sigma on the mean. That is not the relevant thing here. You have to look at the sigma of the width. That gives the range of reasonable values. Again, if I’m interpreting things correctly the statistical analysis used would never hold up for a physics masters degree paper. I’m not trying to be demeaning or antagonistic, just observing the analysis.
You are confusing perturbative QCD with non-perturbative QCD. Perturbative QCD has made mathematical predictions from the beginning. Non-perturbative QCD is a low energy approximation and we know it is only an approximation that actually follows my previous statement precisely. It has been continually refined with complexity added because the early versions were not very accurate.
Sorry, but as a physicist this paragraph doesn’t make sense. Does the Mouflon sheep support or differ from the models used to make predictions about genetic diversity and the size of the human bottleneck? I’ve heard that the Mouflon sheep data differs from the predictions made by those models.