Single-Couple Human Origin 100kya is Possible (Hössjer and Gauger, 2019)

Faith & Science Conversation
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I don’t wish to resurrect dead horses, so hopefully this one is at least still breathing and twitching, but I’m wondering if the more scientifically literate members here could comment on this recent publication from Ola Hössjer and Ann Gauger [1] in which they argue “that a single-couple origin of humanity as recent as 500kya is consistent with [genetic] data”—I don’t find that part controversial—and yet “with only minor modifications of our parsimonious model assumptions, we suggest that a single-couple origin 100kya, or more recently, is possible.” That’s the sticky bit, for me.

From what little understanding I possess about population genetics, most of which was best explained to me by Dennis Venema in the book he co-authored with Scot McKnight, [2] I thought that the genetic diversity and related data observed in our species rules out an extreme bottleneck (single-couple) taking place that recently. Five-hundred-thousand years ago or more, sure, but the Late Pleistocene or later? I don’t properly understand a lot of the terms, parameters, and simulations used in this paper (e.g., what is “targeted adaptive mutagenesis”?) so I am easily dazzled and impressed—but should I be? Have they made a scientifically defensible case?

CALLING ALL SCIENCE NERDS, especially those comfortable with population genetics, and only if you enjoy this kind of stuff: Please evaluate this paper and provide your opinion on the work accomplished by Hössjer and Gauger. I am not predisposed to reject or accept the results, but I don’t want to embarrass myself needlessly by sharing these results with others if it turns out the work is flawed (and I was too simple or naive to catch it).

Thank you in advance for your thoughtful contributions.

John M. Bauer

P.S. Unless I missed it (for I did skim over the really complicated stuff), it seems their argument for a founding couple 100,000 years ago or less amounted to a single paragraph at the end of the paper: “It is beyond the remit of this paper to explore these three and other possible expansions of our parsimonious single-couple origin model for humanity. But in light of the many possible extensions, we suggest that it is possible to fit a model to genetic data, for which the founding couple lived 100kya ago or even more recently.”

Footnotes:

[1] Ola Hössjer and Ann Gauger, “A Single-Couple Human Origin is Possible,” BIO-Complexity, vol. 1 (2019): 1–20. doi:10.5048/BIO-C.2019.1.
https://bio-complexity.org/ojs/index.php/main/article/view/BIO-C.2019.1/BIO-C.2019.1

[2] Dennis R. Venema and Scot McKnight, Adam and the Genome: Reading Scripture after Genetic Science (Grand Rapids, MI: Brazos Press, 2017).

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I’m not a population geneticist, nor do I play one on TV :slight_smile: but of course I’m quite interested in this attempt. I’m competent to evaluate this stuff to a point - but for the nitty-gritty, a real population geneticist would need to weigh in. Paging @glipsnort, and perhaps @T.j_Runyon (or Steve) would like to invite my friend Joe Felsenstein over to BL. There’s also a conversation going on at Peaceful Science, so that’s a thread to watch as well.

So, time for a hot take.

In many ways, it has the same results as the conversation we had here, some time ago, with Richard Buggs. And it looks to have the same basic features, especially that it has to have exactly the right variation in two people (all four alleles different, for everything) and requires exponential population growth, especially early on, to not lose the precious variation from just two people.

In the Gauger paper, we see that they need a population growth rate of doubling every 10 generations in order to get this to work. That is a FAST rate for a prehistoric hunter-gatherer population. That’s a doubling time around every ~250 years. Measured rates are more like doubling every 1,700 years. Now, that paper shows that you can have a rate like what Gauger is proposing for short periods - but for the Gauger model to work you need this rate, uninterrupted, until the population swells to 16,000 individuals. Hmm. That’s a stretch.

I think Ann meant “mortality” there, and that’s a heck of a typo. :slight_smile:

No, the rate that they chose is not “parsimonious”. It’s as high as has been observed over very short timeframes assumed to hold over long periods.

There’s also the issue of how you stop interbreeding, just like we discussed with Buggs (and no one was able to propose a mechanism that obliterated every other hominin on the planet (Africa, Asia) except two. I see that Ann has touched on this in a piece featured at the ID site evolution news:

Really? That needs more fleshing out. The pair stays isolated in a gorge until the population hits 16,000 with exponential growth? That’s a pretty well-stocked gorge. An event that wipes out all but two across two continents (data not shown)? Evidence, please. Same issue we had with the Buggs idea.

So, it seems like a case in special pleading to me. And it shows just how far you have to push things to try to shoehorn present-day variation into just two people. But I’m welcome to be corrected by someone with deeper skills in pop gen. And I’d love to hear Joe, or Steve, weigh in with their thoughts.

Edit to add: the thing about bumping this towards two people at 100,000 years ago - I’m not seeing anything to support that, but it’s probably going to be some attempt to accelerate mutation and recombination rates (since that is what it would require). But I see no attempt to justify that in the paper.

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Let’s see. At 100,000 years ago, sapiens were spread from Israel (Qafzeh) to South Africa (Blombos). I think we can safely rule out that date for a two-person bottleneck.

The whole attempt reminds me of what Graham Coop said about “genealogical Adam” on Twitter: “It’s a neat parlour mathematical trick.”

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Yeah, that’s a very sticky bit. Finding that a model with a 500 kya initial couple is consistent (more or less) with frequency spectrum data is not surprising, especially if you have a loose definition of ‘consistent’ and only look at the folded spectrum (which they do but shouldn’t have). Stating that the founding event could be five times more recent, based on no evidence at all, is absurd.

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That statement would normally never make it through peer review without supporting evidence. It’s in there to be quoted, most likely.

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Genetic theory must have changed radically since I learned it. I was taught that you need a gene pool of at least 60 couples to create a viable population let alone the diversity of all humanity.
Ah well,

Richard

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My impression is that is still true, and Dr. Gauger’s model is pushing the boundaries of possibility even at 500kya. My understanding is that her paper only argues that it statistically could be possible to have had a population of 2 that far back, not that there is any evidence it was so. My impression is that based on gene frequencies and such, the evidence is still most compatible with the population never falling below several thousand in the last 100kya and looking back farther is beyond our current capabilities.
I understand that cheetahs have been through such a narrow bottleneck of 60 or so,
and they are at risk due to lack of genetic diversity.

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Phew! My education was not a waste of time then.

Makes this thread rather academic though.

Or maybe proves what I have been saying about blinkered theories.
People seem to forget other branches of science when making their assertions.

Richard

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Folks might be interested in a write-up I did on this article that was posted to Scot McKnight’s blog Jesus Creed this morning:

And no, I no longer look so young and spry… :slight_smile:

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I enjoyed the article, Dennis. You did a great job of clarifying the paper in such a way that we non-acedemics could understand. I went to the Gospel Coalition article referenced, and it was interesting in contrast how it never discussed how the timing for a single couple to fit the data was 500kya, and that humans at that time were of the species Homo erectus. There was a passing comment of “We say it is possible, not proven, because there are many other things to deal with, like the fossil record.” Yeppers, just a few minor points, like bones and genes and stuff. I hate to say the Gospel Coalition piece was written to mislead the readers, but it has that effect whether intentional or not.

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I’m glad that I wasn’t the only one to notice that. It’s a pretty important part. A lot of folks are going to read that article and think two Homo sapiens in recent history can produce what we see.

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I agree that was an excellent summary for lay-level readers, and yes, this is very interesting – I’m surprised that a bottleneck at 500,000 years would be encouraging for anyone devoted to a young-earth perspective – maybe just those opposed to common descent of humans, which I am betting is a minority compared to those holding a YEC view.

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Ann Gauger is Catholic, I believe. Someone with better knowledge of Catholic doctrine would have to explain whether it requires a literal first couple as the origin of our species. I thought Catholics in general were fine with common descent, but the beliefs of Catholic laity don’t always line up with papal pronouncements. Maybe @AntoineSuarez or @aleo can enlighten me?

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I think @agauger is a Catholic, yes, but I’m not certain. I’ve tagged her and she is of course welcome here to discuss things if she’d like to.

I think it’s fair to say that Ann thinks sole genetic progenitorship is important, and I know that monogenesis is important for Catholics in some way, but the precise details are beyond my ken.

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One of the things I experienced when I was an anti-evolutionist was that I would enjoy arguments against evolution even if those same arguments used premises I didn’t agree with. So, I can see someone who is a YEC taking comfort in this article along the lines of “see, those evolutionists can’t prove we didn’t come from two” - and at the same time avoiding the issue that it requires at least 500,000 years of history.

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Yeah, that sounds familiar. It’s reminiscent of political attitudes of “the enemy of my enemy is my friend.”

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Antoine Suarez was kind enough to answer in his thread, but I thought it was worth pasting here for the benefit of those not familiar with the finer points of the forum.

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No doubt those with Neanderthal or Denisovan DNA are simply less human.

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I sure hope that’s in jest… O.o

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I use italics for my sarcasm font.

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