Adam and Eve: Genealogical Ancestors of What Fraction of Humanity?

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The text below comes from Joshua’s 2018 paper and represents a nice summary of conservative results:

“These two studies represent the most realistic simulations of UGA.58 Building confidence
in the estimates, simulation results were reasonably consistent, even though all models used very low
migration levels. The outliers with the longest estimates use unrealistically low migration across the
entire map. The “high” immigration rate models still use very low immigration rates, but a MRUGA can
arise in as little as 2,000 years. Other simulations are less relevant because they neglect geographic constraints entirely59 or assume only a few kilometers of migration.60”

“In the best simulations,61 the MRUGA is estimated to arise 3,000 years earlier than the required descendants. The IAP is estimated at about 5,000 years earlier than the required descendants. The nearly IAP for Mesopotamia is likely closer to the MRUGA data than the IAP; a conservative number is 4,000 years.62”

For reference, this is approximately three times longer than analytic results assuming random mating.63 The simulation increases estimates over the theoretical results, but not by much."

“These estimates lead to surprising conclusions. For example, consider choosing all those alive in AD 1 (about 2,000 years ago) as the required descendants. An estimate of the IAP is about 7,000 years ago with a MRUGA at 5,000 years ago.64 Therefore, all farmers in Mesopotamia 6,000 years ago who left any ancestors would each be universal ancestors of everyone alive in AD 1 (fi g. 3). The reference to 6,000 years, to be clear, is merely a consequence of the math (4 + 2 = 6 kya) and should not be interpreted as a specific endorsement of somehow locating Adam here.”
[END OF EXCERPT]

These studies assume no divine intervention or “help” with divinely arranged ship wrecks … allowing for one or more Adam descendant to arrive unexpectedly on some distant coast (say, Tasmania or elsewhere).

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I don’t think your paper or the Nature paper did simulations to address the question with an endpoint of zero BCE, but correct me if I’m wrong. Rohde et al. show that as little as 2000 years can work with an endpoint of today, and my read of their model is that it’s based in large part on estimates of migration and on demographics during the last 2000 years. The claim in this thread, which is that “Computer simulations using conservative migration assumption have produced times of about 2000 years,” gives (to me) the strong impression that this estimate of 2000 years is a result from genetics or biology or something like that. But it’s not. It’s based on simulations of how people move, in a model of the world during the first several centuries CE. Again, correct me if I’m wrong here.

I think it is important to avoid extrapolating specific results like those of Rohde at al. into blanket statements about genetics, in response to important questions like the one asked by @Paul.B.Rimmer. His question, it seems to me, is about genealogical common ancestry in zero BCE.

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This is mathematically weak. We have thousands of ancient DNA individuals that are used to trace human migration patterns that shows how inflows of people change the genetic makeup up of whole regions of the world. Genetics is absolutely silent on GAE which is based on genealogy. As you have said, GAE is a theological constructed to match with the Genesis story while preserving the facts coming from science, archaeology, ancient DNA. GAE is purposely constructed to be outside of scientific inquiry. Please ask the amateur theologians why are they using science to investigated GAE? GAE is a miracle. Like all miracles, believers need just to trust their faith and shut their eyes to any cognitive dissonances that they may have. Isn’t that what faith is all about?

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I did not do any new simulations but I did work out if it was valid to extrapolate the 2004 study’s estimates back 2000 years.

That is what I thought too, till I looked closer. The model is only influenced by differences between today and AD 1 in some focused and limited ways. The most difficult place to reach, in their simulation, is always the Hawaiian and Easter Islands. Common ancestry there contributed most to variability between runs. However, 2000 years ago, these islands are not occupied, so we do not have to deal with this uncertainty (which would stochastically increase convergence times substantially if it was relevant).

Perhaps most importantly, they did not model modern transportation and artificially restricted long-range migration. So the simulation is actually modeling fairly local diffusion (with high population structure), not the high dispersion we’d expect over the last 1000 years.

For reasons like these, I do argue that it is valid to extrapolate this back. Of course, that reasoning is subject to criticism, but to be effective in that criticism we have to get into the weeds.

It is based on simulations of how people move, but there is good evidence from ancient DNA (and other sources) that shows that people in the real world moved around far more than they did in that simulation. So the genetic evidence does support logic here. The actual simulation modeled less migration and movement than we expect in the time range we care about for AD 1 ancestry.

Now, one idea I’m curious about is running new simulations parameterized in detail with information from population genetics. That might become possible in the coming few years.

I agree very much about having precision in this. The book, as you know, gets into far more detail, but we will sometimes speak in a more general way on the forum. Perhaps the more precise way to put it is:

The GAE is based on work that models the universal ancestry of everyone today (which converges in just about 2 ky), and makes the case that these estimates can be reasonably applied to estimate the universal ancestry of everyone alive in AD 1.

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That isn’t what faith is about, and it seems to be a distraction from the focused scientific point I’ve made that does not depend on anyone’s personal beliefs.

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No it isn’t. This calls into question your entire understanding of the concept. GAE requires no miracles at all. The only miracle, which is entirely optional, is the fiat creation of two individuals. But GAE works if they’re born naturally instead.

What suggests to you that human migration in the years immediately after 1 BC was greater than that in the years after 2000 BC? There’s certainly ample documentation of lots of major migration during that period.

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Nothing whatsoever, which explains why I didn’t write that.

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Then why would you suppose that a result from migrations starting in 1 BC would be inapplicable to migrations starting in 2000 BC?

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Are you confusing me with someone else who wrote that?

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I don’t think so. You wrote this:

That makes no sense unless you’re questioning the applicability of a model with an endpoint of today (emphasized, even) to a situation with an endpoint of 1 BC. I don’t understand whatever other point you were making in that post, incidentally.

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I guess “questioning the applicability” sounds like a distortion of what I wrote, to me.

My point is this: the model used by Rohde et al. is based on assumptions and parameters describing the world up to today. That world differs from the world of zero BCE by 2000 years. Their model, as I understand it, considers the movements of people throughout those 2000 years. A similar model for zero BCE would consider migration and demographics during the preceding two millenia, at least. Joshua’s comments suggest that he did this (considered them), which is important because it would be ignorant madness to assume that human migration has been the same over those two eras.

The question is not whether I know that migration was “less” or “more” during those eras; in fact that’s the kind of simplistic question we reserve for evangelicals. The Rohde et al. model, as I understand it, was an elaborate simulation of history, not just some calculations of genetic diversity and population. Details of the simulation include continents, migration routes, nodes, etc.; these were the components. It is really shallow and dumb to ask whether people were moving more in 1 BCE than at some other point in time, and not only because 1 BCE is the endpoint.

And my question was not about “applicability.” The model and simulation is surely as applicable to 2000 BCE as it is to 2004 CE. The question was about whether the simulation was done on that era at all, with its known history and features.

You can write whatever else you want about that, but please stop using your inaccurate words to describe what I’ve written. I’ll own any lack of clarity (and I’m sure that’s a big problem here) but I’m damn sick of your projection.

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I think we were just trying to be more precise in our language and clearly represent what actually has been done on this. I appreciated the opportunity to clarify.

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I thought your response was great and should be bookmarked. It includes some valuable comments and clarifications for those interested in the technical aspects of Rohde et al. and how their work can be used. Their paper (in the Supplement) has a lot of detail about their model/simulations, and includes extensive discussion of caveats. For my part, I don’t doubt any technical aspect of the conclusions of the GAE book, but that’s because the book doesn’t make strong claims about dates and because it acknowledges the potential problems posed by isolated subpopulations.

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I don’t believe that’s true. They don’t model, for example, the extensive European and African migrations to the New World. Not much in the way of lengthy sea voyages at all, much less air travel. Mostly it’s just diffusion over land, and fairly short-range averages.

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@John_Harshman its a bit of a middle position. You are right about this,

However, for example, they do specific the opening of migration pathways (and colonization events) in a way that pegs the simulation to present day.

So it is a bit of a Frankenstein. It models some things that tie it to present day, and others that are probably a better model of the past than modern times.

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I stand corrected. You are absolutely correct. GAE requires no miracles at all. Invisible, non-falsifiable, prefect theological construct.

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It doesn’t even have to be theological. The science applies just as well to any random couple from a few thousand years ago, regardless of their names or whether they appear in some myth.

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