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

[DennisVenema]

I’m not a population geneticist, nor do I play one on TV 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.

@Ann Gauger

Our goal was to use as parsimonious a model as possible, to test under a straightforward standard set of assumptions whether it was possible to duplicate current genetic diversity starting from just two individuals.

So we chose population growth curves with an initial doubling time of roughly every 10 generations, until a population of 16,000 was reached, where it held steady. This is a reasonable growth rate, assuming morality (sic) is not high.

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

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:

@Ann Gauger

One can imagine this scenario in a world still populated by other hominids, but the pair was isolated in a valley or gorge; one can imagine a scenario more extreme where all hominids except those two were wiped out.

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.

[Jay313 (Jay Johnson)]

@DennisVenema

Edit to add: the thing about bumping this towards two people at 100,000 years ago

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.”

[glipsnort (Steve Schaffner)]

@John_Bauer

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.

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.

[DennisVenema]

@glipsnort

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.

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

[RichardG (Richard Gillett)]

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

[jpm (Phil McCurdy)]

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.

[RichardG (Richard Gillett)]

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

[DennisVenema]

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:

Adam -- Once More, With Feeling

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

[jpm (Phil McCurdy)]

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.

[DennisVenema]

@jpm

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 .

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.

[Laura]

@jpm

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

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.

[Jay313 (Jay Johnson)]

@Laura

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

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?

[DennisVenema]

@Jay313

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

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.

[DennisVenema]

@Laura

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.

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.

[Laura]

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

[Jay313 (Jay Johnson)]

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.

@AntoineSuarez

As a complement to the quotes of Pope Benedict XVI at the introduction of this thread I would like to post a quote of his address in the General Audience of Wednesday, 6 February 2013, just 5 days before he announced his resignation on the morning of Monday, 11 February 2013.

I think this quote reflects very well the status of Catholic doctrine and papal pronouncements, and shows that Catholic faith does NOT require “a literal couple as the origin of our species” .

“I would like to highlight a final teaching in the accounts of the Creation; sin begets sin and all the sins of history are interconnected. This aspect impels us to speak of what is called “original sin”. What is the meaning of this reality that is not easy to understand? I would just like to suggest a few points.

First of all we must consider that no human being is closed in on himself, no one can live solely for himself and by himself; we receive life from the other and not only at the moment of our birth but every day. Being human is a relationship: I am myself only in the “you” and through the “you”, in the relationship of love with the “you” of God and the “you” of others. Well, sin is the distortion or destruction of the relationship with God, this is its essence: it ruins the relationship with God, the fundamental relationship, by putting ourselves in God’s place.

The Catechism of the Catholic Church states that with the first sin man “chose himself over and against God, against the requirements of his creaturely status and therefore against his own good” (n. 398). Once the fundamental relationship is spoilt, the other relational poles are also jeopardized or destroyed: sin ruins relationships, thus it ruins everything, because we are relational. Now, if the relationship structure is disordered from the outset, every human being comes into a world marked by this relational distortion, comes into a world disturbed by sin, by which he or she is marked personally; the initial sin tarnishes and wounds human nature (cf. Catechism of the Catholic Church, 404-406). And by himself, on his own, man is unable to extricate himself from this situation, on his own he cannot redeem himself; only the Creator himself can right relationships.” (Pope Benedict XVI, General Audience of Wednesday, 6 February 2013.)

This means:

Catholic doctrine requires that the first sin in the history of humanity has consequences for the whole humanity that the other sins don’t have. By contrast it does not require that the first sin is committed by someone from whom all humanity is genetically or genealogically descended.

[mitchellmckain (Scientist and Christian)]

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

[DennisVenema]

I sure hope that’s in jest… O.o

[mitchellmckain (Scientist and Christian)]

I use italics for my sarcasm font.

[John_Bauer (John M. Bauer)]

@DennisVenema

In many ways, it has the same results as the conversation we had here, some time ago, with Richard Buggs.

Yes, that was one of the first things I had noticed. And that is precisely why I said that “a single-couple origin of humanity as recent as 500kya” is not something I find all that controversial—or even remarkable. First of all, when we are talking about that long ago, we cannot be talking about Adam and Eve or that particular biblical context because we know from the textual evidence (farming, walled cities, etc.) that it was far more recent, as you also pointed out in your recent article on this. Secondly, we can’t even be talking about human beings at that point because Homo sapiens don’t appear on the scene until a long time later. In response to arguments for a single-couple origin of humanity 500,000 years ago, I can only shrug my shoulders. Sure, if we play with the numbers just right, maybe it’s possible—but so what? Why would anyone even look for a single-couple origin that long ago? It’s not like it could have been our Adam and Eve, so what would be the point, beyond academic curiosity?

But if you want to move that single-couple origin up to 100,000 years ago “or more recently,” that’s where I’m going to raise a finger, politely clear my throat, and beg your pardon. That’s controversial enough to require compelling evidence. However, as an average blue-collar layman, I find highly technical jargon describing complicated number-crunching really difficult to understand, so I wasn’t able to discern whether or not Hössjer and Gauger had provided it. I’m genuinely grateful for people like you who not only understand this stuff but are really good at explaining it clearly to the average person.

You commented that these sort of arguments illustrate “just how far one has to go to try to make sole genetic progenitorship work.” And I can see that. However, what I don’t understand is why people try so hard to make that work when it’s biblically and theologically unnecessary, as far as I can tell. If Christ can be a covenant representative without anyone being descended from him, then surely Adam can be, too. Or is there something I am missing?

@DennisVenema

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:

That was a fantastic article, sir, thank you. I’m very glad you took the time to write that. After reading your article, I was able to reexamine that paper and comprehend much more of the argument it was presenting. I especially appreciated this particular observation:

Another thing to keep in mind is that at 500,000 years ago, there are no Homo sapiens on the planet. At that time Homo erectus is widespread, so, if we’re talking about a bottleneck at this time, then Adam is not Homo sapiens, but rather Homo erectus or a close relative. It should also go without saying that the Genesis narratives (with their agriculture, domesticated animals, advanced metallurgy, cities, and so on) look nothing like 500,000 years ago, when stone tools were the order of the day.

I also liked your salient question, “If Adam and Eve are created de novo, why does our genome look like we evolved?”

In the book I used the standard, non-specialist convention of referring to humans as Homo sapiens. In science, you will sometimes see “humans” used to refer to all species within Homo, including Homo erectus, Neanderthals, and so on. But for a popular audience, equating Homo sapiens with human is more common, so I went with that approach. When Gauger claims that single-couple human origin is possible, she is using “human” in the broader, all-of-Homo sense – but many people will not understand that and hear “single-couple origin for Homo sapiens”.

Indeed, I am one of those people. I thought she meant Homo sapiens.

@DennisVenema

And no, I no longer look so young and spry

I enjoy speculating that you’re still using that picture because it’s a random picture you grabbed off the internet one day and you can’t change it because it’s actually not even you.

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@jpm

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.

Yes, that is a curious thing. What is motivating the attempt? Is there any evidence for a single-couple origin 500,000 years ago and that’s why Hössjer and Gauger are trying to show that it’s possible? I doubt that there is, for they almost certainly would have explained such evidence. What else could their motivation be, other than the creation narrative in Genesis? If they are guided by some specific evidence. I wish they would share it.

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@Laura

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.

I don’t think any young-earth creationist will be satisfied with this paper. Nothing can happen 500,000 years ago in a universe that is 6,000 years old. This is fodder for progressive creationists and intelligent-design advocates.