RTB Says BioLogos Made Population Genetics Mistake?

Below is a surprising excerpt from Anjeanette Roberts’ recent ariticle,

How Can Christians Disagree over Adam and Eve?

https://reasons.org/explore/blogs/theorems-theology/read/theorems-theology/2019/12/19/how-can-christians-disagree-over-adam-and-eve#author) - DECEMBER 19, 2019

In it she discusses her participation in Jim Stump’s podcast, “The Language of God”. This is an excerpt:

"Venema addresses the genetic data, which Haarsma seems to indicate is what persuaded her not to hold an intermediate date for Adam and Eve. Unfortunately, I think the data and interpretation presented to listeners are filled with inaccuracies. Through multiple conversations over the past two years with computational biologist and founder of Peaceful Science, S. Joshua Swamidass, it has become clear to me that the perspective shared in this podcast is scientifically unsubstantiated.

Recently, in a lecture presented to the RTB scholar community, Swamidass, … explain[ed] how some of the arguments against RTB’s model have included misrepresentations of population genetics that cannot be found in the peer-review literature. For example, it was often reported that population genetics estimates of ancestral population size are the minimum population size, rather than the average population size.

[The link immediately below a post that contains the video of the lecture she mentions above:

[RTB discussion continued…]
However, by modeling population diversity and dynamics (with many evolutionary, mainstream scientific assumptions considered), it is possibly consistent with the evidence that our ancestral population dipped to as low as 10–20 individuals at 200 kya…"

In fairness, the article does get a little confusing when it comes to using the phrase “sole progenitor pair” in connection with an evolving human population.

But these two sentences rather jumped out at me a little further down the page:

"Stump admits the complexity of the discussion, and I readily acknowledge that the BioLogos hosts cannot address all the details. Nevertheless, the RTB model can account for all the points raised above, perhaps with some modifications to underlying assumptions. Yet the hosts do not consider the RTB model in their analysis."

Was this exclusion an accident, or was it more or less unavoidable in view of the BioLogos position against the miraculous mixed in with Evolution?


Thanks for bringing this interesting discussion to our attention.

I think RTB needs to enumerate the “modifications to underlying assumptions” before we can evaluate their model.

Also, I have heard pop gen experts describe an effective population size as quite different from an actual population size. If the bottleneck 200kya points to a minimum effective population at that time, we cannot conclude the actual population was that size. If I have understood the pop gen folks…

Third, all that notwithstanding, a bottleneck to 20 individuals does not support a genetic ancestry converging to a single couple at that time. Universal genealogical ancestry, on the other hand, could easily be much more recent even than that, as @swamidass hypothesizes in his new book.

I would be interested in getting input from a real pop gen expert like @glipsnort. Steve, can you spare a moment from Advent to share your thoughts?

Merry Christmas to all,



Im glad you are getting some expertise on the question (@glipsnort). Frankly, this particular dispute is a little outside my comfort zone.

I can only hope that @swamidass’s video at the PS link would answer your questions!

So I’m guessing peaceful science is a similar group but creationists? I’ve never heard of it except for once before in some other thread. I’ll google them. Guess I’ll have to see what they are saying to completely understand.

Based off what I read in this thread it seemed like they believe that 2 people are responsible for everyone here as common ancestors but at the time argued the population dropped to 20, instead of hundreds, yet that still is significantly more than 2.


Gosh no.

P.S. promotes GAE scenarios where Genesis 1 refers to the human population prior to Adam/Eve …which in the modern view would have originated from primate evolution.

The creations of Adam/Eve are one-off miracles (analogous to the miracles of the virgin birth or the resurrection of Jesus) that don’t overturn science as we know it, yet science is not equipped to refute such small magnitude miracles.

Imagine Christians who support the validity of Evolutionary science.

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I understand now. Thanks. That makes more sense and harmonizes the confusion I was having with Adam and Eve vs 20 or 200 others.

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That’s correct. The effective population size (Ne) is the size in some population genetics model that generates behavior like that seen in the real population. (What you think Ne is can depend a lot on how you estimate it. Humans have a very large variance Ne, but a small Ne as estimated by heterozygosity. If that’s the case, it’s not clear to me that Ne is really a useful concept.) Usually the effective size is smaller than the census size, often a lot smaller. It’s possible for it to be bigger, however, at least in the case of subpopulations that are nearly isolated from one another.

Swamidass is certainly correct on several points. Estimates of past Ne are point estimates of the most likely value at each point in time, which is quite a different thing from a lower bound on the population size. Ne also represents a kind of average population size over extended times, rather than a precise estimate for every generation; this makes it rather insensitive to very short bottlenecks. Whether this kind of thing is enough to allow for RTB’s model depends on what exactly is in that model.

Yeah. A short bottleneck of 20 individuals 200,000 years ago might well be undetectable today (I’m not sure, but it seems plausible), but that’s still a factor of ten off from a single couple.



Thanks, Steve! I hope you and yours had a merry Christmas.

Question - effective population size is denoted N-sub-e like this? Ne And then census population is simply N?

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Thanks – you too.

Yes, that’s the convention.


I wanted to offer some independent comments not necessarily in relation to your post but about the same article (that may end up overlapping at some point).

I find it very curious to begin with and argument from underdetermination.

The reality is that disagreement is not just an issue in science and theology but in all areas of human reasoning and worldview formation. It’s known as the underdetermination of a theory.

The suggestion seems to be that there really isn’t enough empirical evidence to rule out certain hypotheses. Now this certainly occurs with one great example being between the steady state theory and the big bang theory. But this is very curious and literally any group could claim underdeterminism and use it to legitimize their view point. a common talking point of many young Earth creationist is that the evidence really can be interpreted either way. There’s no independent way to go ahead and tell whether or not they’re actually was a flood few thousand years ago that killed everything you cover the entire Earth. We all have the same facts and it’s just based upon one’s worldview. Now any YEC is dead wrong, and this introduction seems like a technical loophole that can exist and will be attractive to many Christian readers who believe various things like common ancestry are still up for debate (which many of these things are not).

I don’t have anything to add for the section titled: Applying Respectful Dialogue in Light of the Underdetermination of Theories. It’s pretty clear by this point the main argument will be that the model she will argue for, the RTB model, is not ruled out by evidence.

After this there is the section that the RTB model, Sole Progenitor Pair at an Intermediate Date, is in fact tenable. A few challenges to the idea were reportedly put forth in the podcast to which Roberts concludes:

Nevertheless, the RTB model can account for all the points raised above, perhaps with some modifications to underlying assumptions… the RTB sole progenitor pair model successfully fits the scientific data and the biblical data within this intermediate range, and acknowledging this would have brought clarity to the general listener.

My first reaction to this is: yeah that’s what they all say. Every young Earth creationist speaker I’ve ever heard declares basically the same thing. That is, any possible challenge to their model can easily be addressed and that their model makes better sense than the others. Since there were no links or articles that went along with this claim, the reader will have to take her at her word but I do find some of these previous examples from RTB interesting:

  • Presenting a paper on the scientific case for Adam and Eve. The article aims to cast doubt on population size estimates by presenting a paper that has nothing to do with effective population size calculations. And this reportedly strengthens the case of the RTB model.
  • Another article on a primordial pair or population. There are 5 specific arguments presented as to why humanity did not begin as a population. We can reject a primordial population because 1) it’s based upon evolutionary bias, 2) the mathematical models are too simplified (no sources or better models/calculations are presented), 3) the models are quite poor at including certain phenomenon and a paper is cited. Remarkably the paper actually strengthens our understanding of population reconstructions and does not disagree with many of the results from previous modeling. 4) Unfortunately the Mouflon sheep of the previous bullet point are rementioned and 5) cites a study questioning whether mtDNA is a reliable predictor of human population size. But an important question which population size papers use mtDNA? I don’t know the answer so let me look for a random paper (this blog will work for now: https://blog.insito.me/arise-the-coalescent-e32501a90524). So then it seems the author just ignores actual calculations and then rejects them due to Adam and Eve being super important theologically.

Finally there is the section “Interpreting Human Population Genetics.” I’m not sure what else to add to this section, but there are a lot of “technical caveats” that despite being possible with maybe some evidence- don’t have evidence to support them. For example, a population dipping to a single couple near 500 kya has no positive evidence, but maybe can’t be ruled out by present evidence. There is also the technical trick where if you count non-homo sapiens as non-human then you can have interbreeding homo naledi or whomever with homo sapien and then the effective population size would include both our species’ populations.

This is an interesting conclusion:

As an RTB scholar I was looking for an acknowledgement that we have an empirically equivalent model that dates a sole progenitor pair to an intermediate date, and that correlates much of the scientific and biblical data within this range.

I think it would be great if there can be an RTB model that does engage with the data, not just what looks like to me as taking advantage of error bars with various measurements. Humans share common ancestry with other species and there is no positive evidence of a bottleneck of two at an ‘intermediate’ date. I think it’s a very big overstatement to conclude that it’s empirically equivalent model to that of population geneticists!


Thanks for pointing that out. I’m not really in a position to parse the data, but that assertion sent up red flags in my mind before I got very far – it sounds like the same old “we all have the same evidence, we just interpret it differently” catchphrase.


And yet you seem to be carrying water from the wrong perspective … and if a non-Trinitarian notices that behavior, you know it’s fairly pronounced.

We have to confess, don’t we?, that Christians already have a bias? - - a bias that disturbs atheists, but a bias that seems quite reasonable for the greater slice of the Christian community, namely: that even when we have been trained in the sciences, Christians are allowed a certain amount of the miraculous, yes?

Peva, if you are a self-confessed Christian, you already accept that Jesus was miraculously born without a biological father… and that he died and was miraculously resurrected.

These are impossibilities if we imagined this kind of thing happening all the time, even into the modern period. But we do not. And believing in these miracles doesn’t over-turn millions of years of fossil evidence.

There are those who question this “slippery slope” - - they say there is no evidence of an orbiting tea pot … so why not believe there IS an orbiting tea pot? Well, I suppose because an orbiting tea pot is not mandated by the theology of atonement, right?

Conversely, while you complain that we are allowing a few more miraculous things to happen … when strictly speaking, this unsettles you … at the very same time, you reject the idea that God invests in natural processes to accomplish his divine will … apparently because this is also unsettling to you.

What kind of divine being do we have here? Nothing but a few allowable miracles, no other miracles that might get confusing - - and no practice of natural laws and processes… because that TOO is unsettling?

From your viewpoint, @Pevaquark, what exactly does God do to occupy his time?

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