Jeanson's Method of Inferring Past Population Sizes

Let’s wait to see if your audience of one follows you here.

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I would love to have tell you I found it, as the idea of those populations being theoretically indistinct is covered in video 2. But I must have remembered incorrectly when they were talking about it because I went through a lot of the first five videos and didn’t find it. It was in a short back and forth, but I remember it distinctly, as it made sense to me that I would make the same mistake. I am ethnically Dutch, and the state church was Reformed. Dutch immigrants brought their church tradition to America with them. But Calvin was in Geneva, Switzerland. And in the back of my mind I always thought that was weird growing up. How did the Dutch state and churches adopt that when he was far away and wasn’t even a citizen of their country? Then it occurred to me after watching this that that part of Europe was really a whole that mixed, and national identity developed after the Reformation. After watching the series, I can now see that certain things happened because of population sizes and weren’t random. That the Renaissance and Reformation happened because population grew large enough, but people were still mixing enough to spread new ideas throughout Europe. And we can do the science we do today because our population is massive and any scientific knowledge is shared around the world.

I will keep looking for that particular section; it’s a bit tough as there is 25 in the series. :sweat_smile:

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I’ll have to read the technical papers to see if this is addressed.

@evograd Testing Jeanson's Model: Y Chromosome Mutation Rates I think here you’re still thinking in terms of the entire genome, not the y-chromosome, if I understand this correctly. I’m not familiar with these.

I believe @Joe_Felsenstein has published extensively on this kind of topic (phylogenetics + estimating population size), if he wants to add to this discussion.

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OK - I took a look at the paper. What I understand from my non-science background is that he said, “I’ll try it out and see if it works. And it works pretty deep in the the tree.” Your diagram shows five generation, so it doesn’t work well on a small scale, I see that.

Here’s a quote from the paper. (My bold for emphasis if I’m understanding the different between shallow branches and deep branches.)
"This formula predicts the frequency with which deep-rooting Y chromosome lineages will be discovered in the future, and it derives from the multiplicative relationships among the known historical population sizes. As figs. 3–5 show, the multiplicative relationships among this historical population sizes match the multiplicative relationships among deep and shallow Y chromosome lineages. Thus, historical population sizes can be used to predict the discovery of deep Y chromosome lineages.

And this:
“As another arena of testable predictions, my results predict that the entire tree should reflect the known history of civilization post-1000 B.C.—not just the global history as a whole but also the history for specific subregions. Prior to 1000 B.C., human history is model-dependent, and, therefore, cannot be used as an independent test of my results. However, post- 1000 B.C., YEC and evolution largely agree on the specifics of human history. My results indicate that the Y chromosome tree should be consistent with this.”

Basically, it’s…“you may not like this, but if it keeps coming up with results, then it’s harder to argue it’s wrong.”

Let me know if I’m understanding that wrong.

(I also saw he got male population by dividing the population from sources consulted by 2.)

Yes, you are. The Y-chromosome tree does not represent population size. Have you looked up coalescent theory yet? Remember the part about the men who have only daughters? The tree must narrow as you go back in time regardless of whether the population is increasing, decreasing, or staying the same.

Further, Jeanson’s population curve is bogus, and there’s nothing special about 1000 BC. His mutation rate puts many ancient divergences within historical times, and that can be checked. His mutation rate is cherry-picked and doesn’t match the great majority of measurements. And of course the archeology to which he appeals shows our species to be at least 150,000 years old, to have originated in Africa, and to have inhabited the entire world at least 15,000 years ago, the Americas being the last-settled continents.

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I’m afraid you are understanding those passages incorrectly. They have nothing to do with the problem I pointed out. The first quote is talking about some potential future predictions of the number of as-yet-undiscovered very deep-branching Y chromosomal lineages that might be able to be made from his model. The second is simply about his model being able to infer region-specific patterns, not just about humanity as a whole.

Neither address the central problem. You pointed out that my diagram is a small-scale scenario, with just 5 generations, but the principle remains even in larger populations and over many more generations. Imagine the same diagram but 100 times wider and 100 times taller, encompassing 500 generations of a population with a constant population size of 800. The branching pattern within would be identical.

Jeanson’s method can only ever show a growing population, regardless of whether the real population remained a constant size, or even went up and down at different points in history.

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I logged in this morning, as I was thinking about this and wondering if I was understanding explaining this wrong: that the y chromosome tree doesn’t represent population size, but it shows its own growth curve that can be matched to population size, since the probability of having a boy or girl is so similar and boys are usually prioritized.

No, that isn’t true, as I’ve been trying to explain. The Y chromosome tree neither represents the population size nor can be matched to population size. If a man has only daughters, his lineage is truncated permanently. In the present day, it will be as if he never existed. The farther back in time, the more the lineages descending from men of that time will have been eliminated. That’s all the tree shows. It says nothing about how many men were in the population in the past. You really need to look up coalescent theory. Here.

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What John H said. What evograd said.

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Well I’m thankful to @thoughtful for bringing this to our attention. I had missed this, and may just not have believed upfront he had done something this out there. I’m reminded of Poe’s law…

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It does say the “entire tree” of humanity and “but also” region specific patterns

After I began to be curious about the scientific process behind Genesis 1, I took a detour into looking into Nimrod from Genesis 10:8-11. In just a few sentences, it gave me enough info to compare the first empire in recorded history, Akkadian empire with the one the Bible also lists as the first. I kept following the rabbit hole in Wikipedia and satisfied my own curiosity that every significant civilization left behind ruins or written records and that tools dated later were just from farmers at the same time. The details are fascinating, but you wouldn’t believe me. Anyway satisfied my own curiosity to not worry about the dating but look at details of the archaeological and written records for clues instead.

You really should worry about the dating, because that destroys Jeanson’s time scale. Aren’t you worried that you ignore everything except the data you find convenient to your preconceptions? That’s not a good way to determine if those preconceptions are correct.

I know, that’s what I said…

If I’m understanding it right, this is perhaps just a worldview problem. Jeanson has less than 200 generations for all humanity, so there would be very few branches that get cut off - like I said, most cultures prize having at least one son, probably many more.

Evolution has a constant population size for millennia, and there would be many branches that get cut off.

Would I be correct in framing it this way?

No. Even from a YEC worldview, Jeanson’s argument makes no sense. It is like arguing 1+1=3. That isn’t true, even if you are YEC.

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Even if we were to grant the hypothetical scenario where no men ever died before having sons, his method still makes no sense. These are the paragraphs where Jeanson tries to justify using a sample of <350 men to reconstruct the last 3000 years of population size changes, but it’s just gibberish:

“Deeper consideration of the multiplicative nature of human population growth further refined this criterion. Mathematically, biblical population growth of males spanned about 9 orders of magnitude— growing from an initial population of 4 men (e.g., Noah, Shem, Ham, Japheth) to nearly 2 billion in 1975. Yet the high coverage dataset that I employed (Karmin et al. 2015) spanned only 2 orders of magnitude (i.e., less than 350 men were sampled). Mathematically, it would seem unlikely that a sample of a few hundred men in the present would permit access to the entire population history of the globe.
Instead, under the second criterion, we might have expected these datasets to capture the most recent 3,000 years of human population growth. For example, in 1000 B.C., the male population was already 25 million. By 1975, this number had grown by only 2 orders of magnitude—to nearly 2 billion. Since the Karmin et al. (2015) dataset represented men sampled in the present and, therefore, represented a look back in time at the population growth that led to these living males, we might have predicted this approach to capture population growth post-1000 B.C. Before 1000 B.C., population sizes would have grown by 7 orders of magnitude—too great a change to be detected by our methods. Thus, we might have expected pre-1000 B.C. population inferences to be a flat line—no branching events due to the multiplicative nature of human population growth.”

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There’s actually historical evidence for this. China used to have a great many more family names than it does now. Family names pass through the male line, and most of them have now become extinct. And of course the Y chromosomes associated with those lines have also become extinct.

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