Adam, Eve and human population genetics, Part 16: addressing critics – William Lane Craig, the historical Adam, and monogenesis (continued) | The BioLogos Forum


(system) #1

Note: In this series, we explore the genetic evidence that indicates humans became a separate species as a substantial population, rather than descending uniquely from an ancestral pair.

In the last post in this series, we began to explore the ideas of apologist William Lane Craig as they pertain to Adam and Eve. Specifically, we saw that Craig holds to genetic monogenesis – the hypothesis that humans descend uniquely from an ancestral couple, rather than a population – in the face of population genetics evidence to the contrary. Part of his reasoning, as we saw, was to suggest that the human mutation rate was once far higher than it is now. For Craig, this includes the possibility that God may have supernaturally increased the mutation rate of the human lineage to account for present-day genetic diversity. With such a miraculously accelerated rate, Craig argues, the genetic diversity we see in present-day humans could in fact arise from just two individuals – the historical Adam and Eve:

In order to calculate whether this amount of genetic diversity could arise from an initial human pair, you have to assume a certain mutation rate that is constant over time. One might deny this conclusion by postulating accelerated rates of mutation in the early human population. One could see this as a result of divine intervention – that God accelerated the evolution of early humans so as to produce greater genetic diversity.

As we have seen, this argument fails to account for calculations of human ancestral population sizes that are not dependent on estimates of mutation rate. An additional problem with this argument is that humans are not merely genetically diverse, but that we observe patterns of diversity in different human populations. Genetic variation in humans is not uniformly distributed across the globe. If you examine Northern European populations, for example, you find certain genetic variants connected to other certain variants in predictable ways. The same holds for any other human population – Han Chinese, populations in sub-Saharan Africa, and so on. It is these patterns of variants linked on chromosome sections that allow us to use linkage disequilibrium to estimate our ancestral population size. And as we have seen, this method returns the same value (~10,000) that other methods do.

The question for Craig, then, is not merely “why are humans so genetically diverse?” but rather “why do humans have their abundant genetic diversity in the particular pattern we observe in the present day?”While the first question might appear to have a simple answer, however farfetched it may be – i.e. increased mutation rates – this answer does not even begin to explain the second question. Mere mutation alone would not put certain combinations of variants into various populations. These patterns are inheritance patterns, not mutation patterns.

Let’s look at an example to help us understand this issue. Suppose one small segment of a human chromosome has four regions where variation is present in human populations. We can represent the chromosome as a line, and mark off the four locations with letters (a, b, c and d). Each of these locations has multiple DNA sequence variants within the population. Suppose for one individual, they have the following combination on one of their chromosomes: they have DNA variant 4 at position “a”, variant 7 at position “b” and so on:

Now suppose we look at other individuals from the same population for these same four chromosome locations. In them we observe new DNA variations present at locations “c” and “d”, and we observe different combinations of those variants:

At locations “c” and “d”, we see two options at each location, and we see a few combinations: (c2 with d6), (c2 with d1), and (c7 with d1). Now the question for the geneticist arises: how did these three possible combinations arise? The basic issue is this: are we looking at the results of multiple, independent mutation events, or mixing and matching of the same mutations into various combinations through genetic recombination? Take for example variant c2: we see this exact variant (down to the precise mutation at the DNA level) in the top two chromosome combinations. The probability that these two chromosomes independently mutated to variant c2 is possible, but tiny. Far, far likelier is that these two chromosomes have the same c2, from a single mutation event in the past that has been recombined into two combinations with different variants at the d location. For example, suppose this population has many individuals with the (c2 d6) combination (first chromosome), but fewer individuals with the (c2 d1) combination (second chromosome). This observation suggests that the (c2 d6) combination is older, and has been passed down from a distant ancestor to more offspring over time. The rarer (c2 d1) combination is likely more recent, and it likely arose by a recombination event. Suppose the third combination (a2 b9 c7 d1) is also common in the population – this is the likely source of the d1 variant seen in the second chromosome combination. The alternative hypothesis is that the d1 variant arose independently twice (or that the c2 variant did) – i.e. the exact same mutation happened twice over. This is much less likely than assembling the second chromosome through the mixing and matching of recombination using the common first and third combinations.

And here’s the rub: the recombination events are also infrequent events. The more closely linked together two locations on a chromosome are, the less frequent recombination becomes. We can directly measure recombination rates in present-day humans and other organisms, and we have a good understanding of how physical separation of two locations on a chromosome is proportional to the recombination frequency between them.

So, not only do we need to account for rare mutation events, we also need to account for rare recombination events - in this case, the breakage and rejoining of chromosomes through the biological process called “crossing over”. While this example uses only four locations, imagine chromosomes that have hundreds or thousands of locations with these sorts of patterns – which is what we see in present-day humans. There are, after all, about 300,000 locations in our genome of 3 billion DNA base pairs that have this sort of variation present, in a staggering array of combinations. That amount of diversity requires a large ancestral population, because it is too improbable to postulate that a huge number of rare recombination events occurred in a small number of ancestors. That number of rare events requires a large population for the probabilities to be reasonable – just as the number of DNA variants we see in present-day humans requires a large ancestral population to allow for rare mutation events to occur.

So, an accelerated mutation rate alone is simply not going to account for those patterns. A normal mutation rate followed by genetic recombination of mutations over time in a large ancestral population, however, easily explains the pattern.

To what end, variation?

I suppose that Craig might reply that we could expect miraculous governance of recombination as well as miraculous acceleration of mutation to maintain the view, in spite of the evidence, that humans uniquely descend from an ancestral couple rather than a population. The question I have, aside from the ad hoc nature of such arguments, is why? Why would God engineer this variation into human populations in such a way to appear to be a result entirely consistent with processes and rates we observe in the present, when there is no functional reason for this variation? After all, we are discussing variation in present-day humans, which means that none of the variation we are discussing contributes to our being human. Humans could be absolutely uniform for these locations in our genome with no virtually impact on our biology, except in rare instances. This is variation that we don’t need or use – so the suggestion that God engineered it into present-day human populations, giving the strong impression with multiple, converging lines of evidence that we are a species descended from a large population, but for no apparent purpose, is frankly baffling.

In the next post in this series, we’ll continue to explore Craig’s arguments about population genetics models and their reliability.

EDIT: We're having some technical issues with our comment boards at the moment. Until they are fixed, the comment board for this article can be found here.


This is a companion discussion topic for the original entry at https://biologos.org/blog/adam-eve-and-human-population-genetics-part-16-addressing-critics-william-l

(Dennis Venema) #4

Thanks for reading this post. I recognize that it is a bit technical - but understanding how present-day genetic variation in humans works is a somewhat complicated subject. If you have questions about the technical details, feel free to ask. As always, other comments and questions are welcome.


(Gregory) #5

William L. Craig is only an ‘apologist’ and not also a ‘philosopher’? That seems to be a rather minimalizing and narrow way to identify one’s communicative ‘opponent’ in this strictly ‘evangelical’ conversation.

“Specifically, we saw that Craig holds to genetic monogenesis – the hypothesis that humans descend uniquely from an ancestral couple, rather than a population – in the face of population genetics evidence to the contrary.” - Dennis Venema

Let’s cut to the chase. Yes or no: Does Dennis Venema affirm, support and/or promote ‘polygenism’, biological/genetic or theological? If not, then what comparable position other than ‘monogenism’ does Dennis accept? Having no position is not a healthy position. Not being able to express a coherent position is devastating to one’s argument.

I have no questions about the ‘technical details’ because they don’t impact my general approach. If Dr. (‘Lord of the Flies’) Dennis cannot answer this directly for a non-biologist audience (99.5% of the population), then what good is his ‘a bit technical’ presentation if not just esoteric? Minimal. Do you think most people care or spend 0.0000000000000000001% of their time thinking about a2 b9 c7 d1?

People want to hear a straight answer to the above question re: monogenism/polygenism/?. Whatever ‘biological/genetic’ knowledge Dennis may share in this thread - because hundreds of other professional scientists [including atheists] around the world would say exactly the same generic ‘settled science’ thing - pales in comparison to him actually addressing that question in terms of ‘science, philosophy and theology/worldview’ conversation.

Is Dennis Venema a polygenisist or not?

p.s. from a sociologist to a genomicist: I don’t think you are even close to this, Dennis: “we are discussing variation in present-day humans”. No, you are focussed on biology. Not people. Not societies. Not communities. Not nations. Not multi-national institutions. It’s best for you to walk back that audacious exaggerated claim. You are talking about only the barest minimum of ‘present-day humans’, as a ‘theist-naturalist’ / ‘naturalist-theist.’ You are far, far from ‘us’ in your genomicist appeals.


(Dennis Venema) #6

Gregory,

This post is one in a long series - and in that series I make my position abundantly clear: biologically, the lineage leading to humans evolves as a large population, never numbering below ~10,000 individuals. This position is one that I have discussed repeatedly on BioLogos, dating back to my earliest posts.

Dennis


(Gregory) #7

Dennis,

I’ve read your work. But you haven’t yet made yourself clear about polygenesis.

Please do so.

Thanks,
Gregory


(Dennis Venema) #8

We descend from a population, not a pair; that population arose once in Africa and spread worldwide from there; some of our ancestors had (limited) genetic exchange with other species (Neanderthals, Denisovans, perhaps others).

That should cover it, unless you’re using some definition of “polygenesis” that I am not privy to.


(Gregory) #9

You brought up monogenesis, Dennis. But are simply not willing to address whether or not you accept polygenesis, biologically or theologically. Is that the situation? Please clarify.


(Brad Kramer) #10

A suggestion, @Gregory. Define both terms as you understand them.


(Gregory) #11

So, in other words, let Dennis Venema off the hook from defining & stating whether or not he accepts polygenesis? It appears that he accepts polygenesis (i.e. he rejects monogenesis). Are you trying to say “that’s ok for Christian theology” according to BioLogos, Brad? Or is that one of the BioLogos ‘Boo’ words?

I’m asking a simple question in the spirit of gracious dialogue. And it is an important question.


(Albert Leo) #12

@Gregory @DennisVenema

Why is it that the answer to this hotly debated question is so clear to me? When asking biological questions about the human phenotype, then the Homo sapien genome demands attention and there is ample evidence for ‘polygenesis’. When dealing with theological or religious matters, it is human behavior that is crucial, and archeological evidence points to human behavior taking a Great Leap Forward by some as-yet-undetermined mechanism, but certainly epigenetic. Thus Gregory’s position that, for religious purposes, the brain-to-mind transition that made it possible for humans to have a personal relationship with God could have begun with a single couple. But Dennis’ position that there must have been thousands of Homo sapiens on earth at that time is also supported by scientific evidence.

So where is the problem?
Al Leo


(Dennis Venema) #13

Gregory:

Historically, “polygenism” refers to the hypothesis that different human populations had separate origins from non-human ancestors, in contrast to the view that humans have their origins in a single population that then spread around the globe. Since I agree with the current consensus that humanity has a single-population origin in Africa, that means I reject polygenesis in this sense. Interbreeding with other (previously distributed) hominins clouds this picture somewhat biologically, but this is still not “polygenesis” in the historical sense of the term, but rather what was historically called “monogenesis”.

Craig, on the other hand, holds to all of humanity descending uniquely from one couple - “genetic monogenesis” for lack of a better term. Note that biologists never used “monogenesis” in the historical sense to intend unique descent from a single couple. I reject Craig’s view because of the ample genetic evidence to the contrary. We descend from a population, not a pair.

If this information doesn’t cover what you’re interested in you’ll have to define your terms as Brad suggested.


(Mohammad Nur Syamsu) #14

I find the “these attributes are useless argument” fairly weak. I guess an argument can be made that the variation serves a function. Computers have a register of random numbers, variation for the sake of variation is functional in computers. You even indicate it serves a function in “rare instances”, after which you say it is of no use.


(Richard Wright) #15

Dennis,

Another great post, and please, don’t hold back on technical discussions, we need the knowledge. Again, great job as always.

Richard


(Albert Leo) #16

@DennisVenema @BradKramer
Sometimes debaters do have a tendency to ‘talk past one another’ because each uses different definition of terms. In a presentation of my personal journey to discover how humans came to ‘know’ God, I phrased it this way:
‘If God made mankind through evolution over a vast number of years, and not all at once in Eden, then at what point did he determine humans were “in his image” and worthy of immortal souls? Animals may have mortal souls, but there is not a gradual transition between mortal and immortal. It’s one big jump. But Darwinian evolution does not take ‘Big Jumps’—end of argument! Or so I thought at the time. But what if Darwinian evolution brought Homo sapiens very close to ‘true humanity’, nearly ready to become God’s image bearer, but not quite there. More on that in Section 2 that follows. "*

Question: Isn’t this really the nub of the discussions prompted by this blog?
Alfred Russel Wallace believed that the process of evolution he espoused could NOT explain the behavior unique to humans. Recently Tattersall, Morris, Diamond, and even Dawkins have expressed similar beliefs. Pope John Paul II stated that the evidence for the formation of animal life through Darwinian evolution was overwhelming, BUT human life was the exception. Is this not a position all Christians can accept?
Al Leo


(Preston Garrison) #17

Pick any scientific theory you want and decide to reject it based on some idealogical commitment. You can then look at any evidence(s) which are inconsistent with your view and insist that God arranged miraculously for things to look the way they do instead of what would be expected on your view. The question is always, “why did God make this adjustment to make my view possible instead of accommodating someone else’s view of what didn’t really happen despite the all evidence indicating that it did?” Different individuals draw the line in different places on what they will accept from science - some accept deep time and reject evolution, some accept evolution of animals and not humans. Some accept evolution but insist it all happened in a few centuries since they are committed to a young earth. I have run into one guy who accepts the account of human migration out of Africa over the last 60,000 years or so (he likes genetic genealogy,} but rejects evolution of humans.

When you see the apparent arbitrariness of what is accepted and what isn’t, varying as it does from one person to the next, it starts to look like it isn’t really evidence and argument that are determining things. It seems as if it’s just individual psychological factors motivating the drawing of a line somewhere. The strategy after that is always the same. “God changed things to give the evidence we see, but my view is the truth about what happened.”


(Gregory) #18

The conversation is approached as one of ‘science and faith’, not only of biology or population genetics.

“Craig, on the other hand, holds to all of humanity descending uniquely from one couple – ‘genetic monogenesis’” – Dennis

I haven’t read or heard Craig giving a clear statement about what Dennis calls ‘genetic monogenesis’, though Dennis attributes this to him. But my understanding of Craig’s position, consistent with ‘traditional’, ‘classical’, ‘orthodox’ or ‘catholic’ (TCOC) Christian belief, is that he accepts ‘theological monogenesis’ and thus rejects ‘theological polygenesis’. So, yes, the definition of the terms ‘monogenesis’ and ‘polygenesis’ is at issue (and if anyone would like to propose a third (or other) alternative term, now is the time to do so).

Thus, when Dennis starts his response with “Historically, ‘polygenism’ refers to…” one might wonder which ‘historically’ he means and if he is closed to other conceptual ‘histories’. Here’s one example of a different meaning of ‘polygenesis’: “Polygenism is a theory of human origins positing that the human race descended from a pool of early human couples, indeterminate in number.”

Similarly, the following definition of ‘monogenesis’ is not about ‘genetic monogenesis’, but rather about ‘theological monogenesis’: “monogenism … posits a single origin of humanity in Adam and Eve.” Or is it possibly about both (nod to @aleo)?

Brad, and now Dennis, asked for my definitions. Here is what I wrote (updated) at BioLogos in 2012.
Definitions on the topic of anthropogenesis:

Monogenism – descent of ‘human beings’ from a single ancestral pair;
Polygenism – descent of ‘human beings’ from a large initial population (or multiple initial populations, according to the multi-regional hypothesis), i.e. a population bottleneck for ‘human beings’ has a minimum size of (much) more than two ‘persons’.

To this, Ted Davis responded: “If I use your definitions above, then polygenism is IMO more likely; at least that is what the scientific evidence is presently said to favor.” Ted’s response, however, only addresses ‘scientific monogenesis’, but not theological monogenesis’. I wonder if in the meantime Ted has read the article by Catholic philosopher Ken Kemp that I recommended to him and also if Dennis Venema has read it because it ‘marries’ scientific (e.g. genetic & palaeanthropological) with theological monogenesis, which they both seem to disallow.

“Since I agree with the current consensus that humanity has a single-population origin in Africa, that means I reject polygenesis in this sense.” – Dennis

Dennis and I agree on the consensus rejection of that kind of ‘polygenesis,’ i.e. multi-regional human origins. Does this mean it is only that narrow definition of scientific monogenism he accepts, whereas he rejects the Church’s TCOC teachings which embrace a wider tradition of theological monogenism? It seems that Dennis is either unaware of or confused about the so-called ‘problem of polygenism’ for anthropogenesis theologically.


(Albert Leo) #19

Brad

I believe BioLogos is very fortunate to have Dennis, a recognized expert in genetics, to present clear evidence for the fact that mankind today owes is genetic heritage to thousands of ancestors, not to just one couple. A careful reading of the replies to this and previous blogs makes it clear that many Christians are aware of this evidence but still cannot believe that humans were created by the gradual process of evolution. I have tried to present evidence from recognized paleoarcheologists that points to a satisfactory merger of both views: Darwinian evolution is responsible for our biological nature; our spiritual nature (what makes us truly human) appeared suddenly by some ‘mechanism’ as yet unknown to science.

And you say this is “only the barest mention of the topic at hand.” Please state your disagreements with it, but don’t call it irrelevant.
Al Leo


(Gregory) #20

As a particular field of study or theory within evolutionary biology, population genetics by definition pays no attention to ‘non-populations’, i.e. individual entities. That fact in a ‘science and faith’ conversation seems to be as simple as confronting John Stott’s homo divinus model (discussed previously at BioLogos) and hinges on what one believes about Adam theologically, not biologically, that is, both as an individual human being (i.e. a ‘person’) and as a signifier for ‘the human race’. Intentional moves to try to biologically erase historical Adam and Eve using population genetics as ‘evidence’, however, also have consequences for theology.

“biologists never used ‘monogenesis’ in the historical sense to intend unique descent from a single couple.” – Dennis

Yet that’s what TCOC theologians mean by the theological monogenetic creation of A&E by A&E’s Creator. They do not endorse theological polygenesis (unless in the rare case when one may be speaking about the possibility of life on other planets, i.e. other ‘A&Es’). So on that front, Craig of course is correct and faithful to the tradition regardless of whether or not he rejects ‘genetic monogenism’ as Dennis suggests.

Let me provide a different example. If ‘autonomous’ Artificial Intelligence is ‘created’ or ‘invented’ in different locations around the world by different ‘scientists/technologists’ at different times, using different materials, that would be an example of ‘AI polygenesis’. Instead, if one ‘race’ of ‘autonomous’ AI were to be ‘created’ or ‘invented’ that spread out from a single source prototype, that would be ‘AI monogenesis’. And if the ‘creators/inventors’ of that ‘first entity’ named it ‘Mada’, then technically speaking, all of the future AI race could be said to have ‘descended/ascended’ from Mada.

The problem here seems to be that Dennis both rejects (multi-regional hypothesis) and embraces (only populations, never individuals) polygenesis, just as he both embraces (uni-regional hypothesis) and rejects (only populations, never individuals) monogenesis. And likewise, he may or may not believe in theological polygenism, though I’ve never read him directly face this topic. That’s why I asked him about it specifically in this thread after he challenged Craig’s ‘genetic monogenism’. Dennis seems to be stuck in a ‘science & theology’ contradiction by accepting both monogenesis and polygenesis at the same time.

If there really is no type of polygenesis at all that he affirms, then he should say so, without leaving out one or two of the major realms of science, philosophy and theology/worldview. However, it seems that he both embraces and openly promotes (e.g. this series) the notion of ‘theological polygenesis’ quoted above. (For more info about ‘theological polygenism’ see here)

In a more balanced ‘science and faith’ or ‘science, philosophy and theology/worldview’ conversation, no matter what the genetic evidence says about populations and individuals, on the question of ‘theological genesis,’ we ‘descend/ascend’ from a single created Adam and Eve; a pair, not a population.

The main point (which returns to @aleo’s question - “So where is the problem?”) is: who gets to define the anthropic ‘we’ of Adam and Eve: biologists, (palaeo)anthropologists, philosophers or theologians and clergy?


(Albert Leo) #21

Gregory
Thanks for the reference to Ken Kemp’s paper. I had missed it, but I am glad I am not alone in emphasizing the importance, when discussing Origins, of distinguishing the source of genes from the source of behavior. I am surprised that Kemp made no mention of Teilhard or Mathew Fox and “Original Blessing”. He did point out that, in light of Pius XII’s encyclical that entrenched Original Sin in Catholic dogma, John Paul II could hardly hedge when he accepted Darwinian evolution for animal life.
Al Leo


#22

Gregory, I think you’re cutting off discussion with your definition. Population genetics is not within evolutionary biology, at least in the sense that if one does not accept evolutionary theory one can simply ignore it. Populations have genetic variation in real time that can be and is often measured directly.

It’s quite empirical.