Adam, Eve and human population genetics, Part 15: addressing critics – William Lane Craig, the historical Adam, and monogenesis | 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 few posts in this series, we have looked at the arguments of Vern Poythress as they pertain to human common ancestry, population genetics, and locating Adam and Eve in human prehistory. A second well-known apologist who has also interacted with these data is Dr. William Lane Craig. Like Poythress, Craig is an Old-Earth, progressive creationist who holds to the view that all humans descend uniquely from Adam and Eve – though Craig is more open than Poythress to the possibility of humans sharing ancestry with other forms of life. To his credit, Craig is aware that he is not an expert in this area, and often assumes a humble posture when discussing these matters:

So some sort of a progressive creationist view, I think, would explain the evidence quite well. It would allow you to affirm or deny if you wish the thesis of common ancestry and it would supplement the mechanisms of genetic mutation and natural selection with divine intervention. I find some sort of progressive creationism to be an attractive view.

Again, I want to reiterate that on these issues I am like many of you a scientific layperson. I am someone who has an interest in these subjects, I want to learn and to study them further, and explore them more deeply. So these opinions are held tentatively and lightly and are subject to revision.

I have had the opportunity to meet Dr. Craig in person, and found him to be thoughtful, congenial and interested in learning more about how modern genetics plays into the conversation about the historical Adam and Eve. While Craig has learned about—and has correctly understood the impact of—the genetic evidence for human common ancestry, his understanding of the evidence from human population genetics is lacking in certain respects. These misunderstandings, unfortunately, lead him to make some basic errors. As he sees it, holding to a historical Adam—in the sense that all humans descend uniquely from an original ancestral couple—remains defensible, since the conclusions of human population genetics are based on assumptions open to critique:

[Geneticists] look at the amount of variability in the genetic structure and then you calculate how this could have arisen based upon mutation rates and the amount of time available. That will then give you these population estimates. But there are quite a number of assumptions that go into this kind of modeling that the defender of the historical Adam, I think, could challenge.

Craig’s defense of a historic Adam and human descent from an ancestral pair (i.e. genetic monogenesis) thus rests on the idea that there is reasonable uncertainty in population genetics measures:

What we need to understand is that these are genetic estimates based upon mathematical modeling and projections into the past. We know that that kind of mathematical modeling is based upon certain assumptions that may or may not be true, and can sometimes be wildly incorrect in their projections… It could well be the case that these mathematical models are simply incorrect.

Moreover, Craig advances the opinion that this uncertainty is great enough to allow one to hold to genetic monogenesis:

When you think about it, it is really quite remarkable, it seems to me, that with these models they are able to get the minimum human population size down to a couple thousand people. I mean, that in itself is astonishing. It wouldn’t take a great error to go from two thousand to two, I think.

So, what “assumptions” does Craig have in mind? Two major themes in Craig’s interaction with population genetics evidence are (a) that population geneticists assume a constant mutation rate for the human lineage, and that (b) population genetics models have been shown to overestimate real populations whose actual demographics are known. We will deal with these issues in turn.

Accelerated mutation rates?

Craig posits that mutation rates may not have been constant over human history, and that in the past mutation rates may have been much higher. Such accelerated rates, he argues, could indeed produce the genetic diversity we see in the present day starting from only two people:

The problem is the population size. In order to get this amount of genetic diversity, the claim is you needed to have at least 2,000 people originally to result in this. One of the assumptions that is based upon is that the rate of mutation doesn’t change. But if the mutation rates are changing then they could accelerate and that could produce greater diversity than one might expect. You might say that increasing diversity would have a selective advantage so this perhaps would be a kind of accelerating process. Again, we just don’t know that these mutation rates have been constant over all of these thousands of years.

There are, of course, several problems with this line of argument (not least that genetics indicates that we descend from a population of about 10,000, not 2,000). First, it is an ad hoc line of argumentation – the argument is made only because the evidence does not fit with Craig’s prior expectation that we all descend from an ancestral couple. Second, there is indeed good evidence that the mutation rate our lineage experienced has not changed appreciably in the last several million years.

There are several independent ways to estimate human mutation rates. An excellent overview of the various methods can be found at this series of blog posts by Larry Moran, a biochemist at the University of Toronto: the biochemical method; the phylogenetic method, and the direct method. For our question at hand, the phylogenetic method is of particular interest: it estimates the mutation rate on the human lineage since our separation from chimpanzees. In brief, we can compare the differences we see in the present-day human genome, the present-day chimpanzee genome, and using reasonable estimates of generation times, infer the number of mutations per generation in our lineage, as well as in the lineage leading to chimpanzees, with both lineages descending from a common ancestral population. This estimate is an average for our lineage over the last several million years – and it agrees well with the estimates we see using the biochemical and direct methods. Even the best-case scenario for Craig— that no mutations occurred at all in the lineage leading to chimpanzees, and every difference between the genomes of our two species resulted from mutations in the human lineage only—does not provide a mutation rate high enough to account for the diversity we see in present-day humans assuming they descend from an original pair.

Finally, only some techniques used to measure human population dynamics over time employ estimates of mutation rates. Other methods—which do not use estimates of mutation rates—return the same results as mutation rate-based methods. One such example is one we have discussed: estimating human population size over time using linkage disequilibrium. Craig’s argument thus needs to explain why these methods agree with mutation-based methods, since speculating about mutation rates does not affect these measurements. Craig also needs to address why the various independent methods used to measure the population size of our lineage agree with one another: if indeed we all descend uniquely from an ancestral pair, why is it that these independent methods all return the same values? The reasonable conclusion is that these methods are telling us something valid about our evolutionary history. These methods and their conclusions are subject to revision and refinement, of course—but unlike Craig hopes for, it is not reasonable to expect that that refinement will reduce our ancestry from 10,000 to two.

In the next post in this series, we’ll examine Craig’s second claim: that population genetics models have been shown to overestimate known population sizes.


This is a companion discussion topic for the original entry at https://biologos.org/blog/adam-eve-and-human-population-genetics-part-15-addressing-critics-william-l

(Dennis Venema) #3

Thanks for reading this post. I welcome your thoughtful questions, critiques or comments - though be aware that I am currently not in my usual time zone, so North American readers may see a delay in my responses. :slight_smile:


(GJDS) #4

A few points that show your arguments are also weak when discussing the theories put forward regarding modelling of human populations’ growth, and extrapolating this to discussions on Adam and Eve:

(1) On the assumption that Adam and Eve were two unique humans created by God for the purpose outlined in Genesis, the argument of whether there were other human beings on the planet, or if there were none, becomes irrelevant to Genesis.
(2) Models such as discussed by Rohde et al, “Modelling the recent common ancestry of all living humans”. Nature 431: 562-566, show a very large amount of data on human populations can be modelled without a recourse to your assumptions. Surely this shows legitimate doubt regarding modelling techniques used on this subject.
(3) The debate regarding a number of various models has continued over many decades. While it is understandable that each of these models will have its supporters and detractors, this situation is very different from the one you constantly portray, that of almost universal agreement between scientists, and lame and perhaps ignorant criticisms from non-scientists. It is one thing to support a particular model, and another to claim universal agreement as you imply in your posts. For example, one paper which proposes the out of Africa models, commences with the statement “The origin of living Homo sapins has once again been the subject of much debate.” in C. B. STRINGER AND P. ANDREWS, “Genetic and Fossil Evidence for the Origin of Modern Humans.” Science 2015. There are responses to this paper, consistent with a somewhat strident debate, and counter responses include statements such as, “Thus they do not provide consistency of approach or genuine testability for their ideas. Without a dear conception of what they mean by “modem human,” they are unable to provide appropriate data on ranges of variation in “modem humans,” (Science 2015).

I am not interested in a protracted debate of argument – my objection is to the way this subject is presented in BioLogos, and this I summarise as, “scientists agree these models are reliable but lay-persons and religious ones cannot understand this”.


(Dennis Venema) #5

Hi GJDS,

on your points:

(1) Craig very much feels that genetic monogenesis is important, as his writings clearly show. So, he would dispute your assertion that the question is irrelevant.

(2) Much of the data presented here does not depend on “my assumptions” - if by that you mean common ancestry. Linkage disequilibrium studies do not assume common ancestry, for example. You do not state what you mean by “my assumptions” though, so I’m not sure if that is what you mean. Note that an “assumption” in science is not typically a wild guess, but a position founded on evidence. I assume that Mendel’s laws will apply to heredity, for example, even if I don’t test that assumption in every cross I make with Drosophila in the lab. It’s an assumption in the sense that it is well enough established that it need not be endlessly re-tested over and over again. Common ancestry is an assumption in this sense.

I don’t see how it follows that modeling human dynamics in ways that does not assume common ancestry throws doubt on methods that do. Perhaps you can clarify. One of the points I make is that all methods employed to date give population numbers that agree with one another - methods that assume common ancestry, and methods that do not; methods that use estimates of mutation rate, and methods that do not; and so on.

(3) The “models” you are discussing seem to be paleoanthropological models (out of Africa, multi-regional, etc) - at least as far as I can tell. The genetics I am discussing here does not presuppose either model - it simply asks how many ancestors are needed to account for present diversity.

I have read the literature on this thoroughly - and no one in the scientific community proposes that the data is consistent with us descending uniquely from two people. Only Christians argue for this, and for theological reasons. If you know of a case where a scientist working in population genetics has published in a mainstream journal that we can explain current diversity as the result of descending uniquely from an ancestral pair, please let me know - I would very much like to read and evaluate it.

Best,

Dennis


(GJDS) #7

@DennisVenema

Hi Dennis,

The central topic as I understand it is that of Adam and Eve - my take on your articles (perhaps you may correct me on this) is that population modelling is so well established that we may present various theories re Adam and Eve that are based on such modelling. My response has been that (a) I do not see where we can accept such modelling with so much confidence ( I am not suggesting the various models are all without any scientific merit, nor should we assume they are free from scientific doubt) as to require a novel theory for Adam and Eve, and (b) any argument for modelling the human population as derived from a unique pair of man and woman also has its problems within the debates by relevant scientists.

Thus, my focus has been on Adam and Eve as stated in Genesis without a need to elaborate, and for those who see a need for elaboration, I want to point out the various approaches to population models, which include an example which does not require a basis in genetics variations and such; thus such modelling cannot be accepted with total (scientific nor religious) confidence.

Hope this clarifies my comments. Best wishes.


#8

Thanks for this extended interaction with Poythress and Craig Dennis: it has been really interesting and enlightening in a number of areas, not the least of which is how to charitably disagree with another brother or sister in Christ.
At your presentation a while back at TWU I think you said it best when statung that being both a geneticist and a Christian at your level outs you in a very small category of people (not bragging in the least, just stating a point). It’s troubling just how many feel adequate to “wade right in” to subjects that are of interest to them, but about which they do not yet have sufficient knowledge to do so in any authoritative sense.


(GJDS) #9

Perhaps it would be useful to comment on the notion of authoritative comments in relation to posts such as given by Dennis. I feel that I should point out that I have developed many simulations and models over a number of decades that have relied on well understood data in my field (not in biology or populations, but the maths in my area is at least as demanding), but I am not seeking to use any sort of authority in these comments. My focus has at all times been on how we may understand scripture - in this context, any authority that I may claim (or any other scientist) is not all that relevant. This in no way diminishes anyone’s standing in any discipline of the sciences - but this point requires restating - scriptural authority to an Orthodox Christian is central to discussions on the Faith and such authority is provided by the Church, and only the Church.


(Dennis Venema) #10

Thanks for the clarification, GJDS. Yes, I am saying that population genetics models are well-enough supported that the probability of them being revised to allow for genetic monogenesis is vanishingly small. So, I do feel it is time that those in the church begin to wrestle with these data, not merely deny their validity (without fully understanding the science).

I too agree that scriptural authority is paramount - but I do not feel that scripture requires a commitment to genetic monogenesis. Here you might find the work of John Walton (Lost World of Genesis One; Lost World of Adam and Eve) interesting and/or useful.

Best,

Dennis


(GJDS) #11

Thanks Dennis - I cannot find the term “monogenesis” in scripture :smile: so I cannot comment on such a commitment. I am puzzled however, at the silence on/or resistance to/or lack of preference for/ the doctrine that God created Adam and Eve and placed them in Eden where they were free from the ills that besets us to this day. I am also bemused by the inference that notions of true humans populating the earth is at all problematic regarding any scientific hypothesis and/or modelling pf population genetics.

Cheers


#12

From the first time I heard the postulation that humans descended from a minimum population of 10,000 people, I questioned the logic. I have never yet heard it explained how it is impossible for the population to be smaller, even though we could logically expect it to be smaller. For example, a population of ten thousand would be presumed to have come from a population of less than ten thousand, unless every pair of parents had no more than two children, and then died before they had grandchildren.

The additional suggestion from this hypothesis is that one day, no humans. On day two, ten thousand humans. Regardless of the minimum population required to contain the diversity presently exhibited, which it seems to me what the modelling is really saying, this does not definitively decide what the size of the original population was. We could merely believe that the original population size was smaller, with less diversity, and the diversity being added later. Regardless of the time involved in adding the diversity (presumably thru mutations), this would be more reasonable than to propose that the minimum population size was 10,000 beings.

The other way to address the illogic of this position (of minimum ancestral population group being 10,000 beings in size), is to define the consequences of such a thought as I did above… one day, no humans, day two, 10,000 spontaneously arrived humans. Or, alternatively, one day all beings were non-human, day two 10,000 of these beings were human.

Perhaps there is a reasonable explanation, but I have not yet seen one.


(Albert Leo) #13

[quote=“GJDS, post:11, topic:732”]
the doctrine that God created Adam and Eve and placed them in Eden where they were free from the ills that besets us to this day.
[/quote]@GJDS Since there is absolutely no scientific evidence that any of our ancestors were “free from the ills that beset us to this day”, it seems to me that the only way that evolution can be considered by clear-thinking Christians as the method that God used to create us is that He created the genome (i.e. the biological nature) of Homo sapiens via Darwinian evolution, but human behavior (Human Nature) was a gift given to perhaps just a couple (Adam & Eve) who spread it epigenetically to the others. We all inherit the genes that makes us prone to sin, but we each take the responsibility for ignoring the gift of conscience that actualizes the sin.
Al Leo


(GJDS) #14

@johnZ

I have tried to address the published modelling on this subject tangentially, because I am acutely aware of both the strengths and pitfalls of simulations and modelling that we may undertake. When considered in a general manner, the ‘thinking’ that we may obtain from population modelling leaves me with many questions, including how we can even discuss a beginning for any model, the basis for the so called bottleneck, how to find scientific data on a dispersion of any relatively small number across regions that cover Africa, Asia, Europe, why they should disperse, the ‘backward’ reasoning to account for the genetic diversity (which can only be verified for present day genetic diversity amongst samples of humans), just to name a few areas where a modeller may be questioned.

In my experience, simulations are inevitably carried out for one very obvious fact - we simply cannot deal with the complexity of the actual phenomena, and a scientist must resort to simplifications and intuitively acceptable limitations/artificial boundaries. This is the main reason why I suggest caution when relying on things such as population models, to add or take away from Genesis. Additionally, the Genesis account can be read to infer the presence of other people, but if this is taken into account, it is treated as peripheral.


(GJDS) #15

I guess the simplest response to this is the obvious one - the absence of scientific evidence cannot be taken as a basis for any speculation or hypothesis.


(Brian) #16

GJDS,

The article by Stringer and Andrews that you quoted from in your first post was published in Science in 1988, not 2015 as you stated. The complete article reference is: Science 239, 1263-1268 (1988). The article you cited by Rohde et al. was published in 2004. You didn’t give a year for that article. Details like these matter because a lot of research has been published in the genomics field even in the past 10 years.

Best,

Brian


(GJDS) #17

@bgreuel

Brian, Thanks for pointing this out - you are correct; I had used the downloading data by mistake (i.e. Downloaded from www.sciencemag.org on January 23, 2015), but the article is dated 11 March 1988, vol 239. pages 1263-1268. I also agree that a great deal of additional research has been published and I am going through a few more recent papers as time permits. The articles by Rohde et al. are:
Rohde DLT, Olson S, Chang JT (2004) “Modelling the recent common ancestry of all living humans”. Nature 431: 562-566
Rohde, DLT , On the common ancestors of all living humans. Submitted to American Journal of Physical Anthropology. (2005). I have not referred to the 2005 paper in the post.

I appreciate your diligence. Best, George.


(Richard Wright) #18

Hi Dennis,

As I’ve stated before, I love your stuff and look forward to reading every new article that you put out. Thank you so much for taking the time out of your busy life to thoroughly and honestly explain genetics as related to evolution in ways that we lay-people can understand - you’re probably the best at that that I’ve seen. I also like the way you carefully counter your opponents’ arguments - with Christ-like grace and respect. And beyond that, you’re one of the few writers here that respond, again with gentleness and respect, to practically every comment. Keep up the good work and look forward to your next post!


(Dennis Venema) #19

Hi JohnZ - you’re thinking in discontinuous terms - you need to think in continuous terms. It’s a bit like saying “Day one , you’re a child; day two you’re an adult.” It doesn’t work that way.

Populations change gradually over time, over hundreds and thousands of generations. Biologically, we became human through this sort of incremental process. There is no clear biological demarcation between “human” and “non human”, just as there is no clear demarcation between “child” and “adult” - it’s a continuum.

And, all the population data is telling us is that we maintained a large population size as this happened.


(Dennis Venema) #20

Thank you for the encouragement, Richard. I’m glad you find these posts helpful. :slight_smile:


#21

Dennis, I don’t know whether to agree or disagree with your comment. Yes, I am thinking in discontinuous terms, but I am also thinking in continuous terms. I think I showed this quite clearly in the comment, “***Or, alternatively, one day all beings were non-human, day two 10,000 of these beings were human.***” This is the continuum. I believe you have not understood the implications. The proposition that the smallest original human population would be 10,000 presupposes that the population of these “undefined” progenitors was the same size, but non-human. That they all originated as humans on the same day… let us say within the same generation, and that they all had analagous and similar changes and mutations and spirits at the same time. If this change happened over thousands of years, then obviously some would have been human long before others, and the original human population would not have been 10,000, but much less, for thousands of years.

But from a genetic perspective, the selection of this genetic prehistoric time is arbitrary, and only based on the diversity we see today. For those who accept common descent, the genetic ancestry is not dependant on present diversity, since obviously everything descended from something different, not just from something similar. Thus it is arbitrary to say that a minimum population of 10,000 would have been the first humans.


(Albert Leo) #22

@johnZ When you judge the non-human -> human transition by genome, the change ought to take many thousands of years; when you judge it by behavior (language, art, grave goods) it appears to have taken much, much less.
Al Leo