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’ve explored William Lane Craig’s objections to the scientific evidence that humans descend from a sizeable population, rather than uniquely from an ancestral couple. And as we have seen, Craig’s objections have not held up to close scrutiny thus far.
One claim made by Craig that we have not yet addressed in detail is this: that population genetics models have been shown to significantly overestimate the ancestral sizes of real populations where their real genetic history is known. The main example that Craig proffers in support of this claim concerns a scientific study examining a population of invasive sheep on a remote island in the southern Indian Ocean.
It’s little wonder that this study caught the attention of those wanting to hold to humanity descending uniquely from a single ancestral couple. In the 1950s, a population of domestic mouflon sheep was founded on Haute Island in the Kerguelen archipelago with a single ram and a single ewe, both introduced as lambs. The extreme remoteness of the Kerguelen archipelago (over 3000 kilometers to the next inhabited island!), coupled with the continuous monitoring the islands have had by French scientists, ensures that no other sheep have been introduced since the population was founded. As such, this population genuinely has the sheep equivalent of a genetic “Adam and Eve” in the sense that Craig maintains for humanity. Even more exciting, though, was the finding that the sheep on this island have higher levels of heterozygosity – which we will discuss in detail later but for now can think of as one measure of “genetic diversity” – than a certain mathematical model predicts. For an apologetics-minded approach, it seems tailor-made: population genetics models overestimate the heterozygosity of a population known to be founded by only two individuals – and thus measurements of human population sizes might similarly be overestimates, and we can hold on to a literal Adam and Eve who were our sole genetic progenitors! This basic argument first appears in the Christian anti-evolutionary literature in 2010, in the work of Reasons to Believe (RTB). Since then, it has appeared in numerous places online, though Craig is basing his argument primarily on RTB sources. As we will see, his argument is not a valid one. It is based on a significant misunderstanding of the study in question, and population genetics in general – but it will take some effort to explain why this is so.
The study shows that the Kerguelen sheep have higher heterozygosity than expected, and show an increase in heterozygosity over time.
This claim is true, but Craig misunderstands why it is true, as his second claim shows:
The observed increase in heterozygosity is attributable to an increased mutation rate driven by natural selection.
This (erroneous) claim is repeated several times as Craig discusses this study. Some examples include:
So natural selection actually accelerates the rise of genetic diversity because it has survival value in the struggle for survival.
In other words, had they not known that there were originally only two sheep placed on that island, looking at the genetic diversity exhibited by the present sheep using the mathematical models they would have over estimated the minimal size that that population would have had at any time in the past because the models did not take account of the accelerated rates of genetic mutation that were driven by natural selection.
This claim is simply false: natural selection does not, and cannot, increase the rate of mutation, however beneficial an increase in mutation frequency might be. Natural selection acts only on genetic variation that already exists in a population. Craig has confused an increase in heterozygosity over time with an increase in mutation rate over time. In fact, as we will see, an increase in heterozygosity over time does not require any new mutations at all.
Natural selection therefore may have driven an increased mutation rate in the human lineage, and an appeal to divine intervention for increasing human genetic diversity may not be necessary.
If so, then population genetics models may underestimate human ancestral population sizes because they fail to account for natural selection. If so, then the “traditional view” that we descend uniquely from an ancestral couple remains defensible.
You might recall that Craig has been attempting to argue for an increased mutation rate in the human lineage in order to explain how humans are so genetically diverse today (leaving aside our discussion that a mere increase in mutation rate is not adequate to explain the pattern of variation we observe in humans). He clearly has this issue in mind when invoking the mouflon study:
If it is the case that natural selection can drive the increase in genetic diversity then that calls into question the assumption that the mutation rates have been constant over time for humanity, and hence it calls into question the population estimates based on that assumption.
The Kerguelen sheep study thus does double duty for Craig: it offers, in his mind, a natural explanation for increased mutation rates, and simultaneously throws human population genetics models into doubt. Since alternative views that accept that humans descending from a population raise theological challenges for him, he sees this evidence as reason not to be “forced” to accept such a view:
… I am just saying that realize that all of these alternatives have really interesting and unsettling theological reverberations that we need to be aware of. So that is an alternative that some people have suggested. What I am arguing right now is I am not sure we are forced to that alternative because I am not convinced that the evidence is inconsistent with there being an original historical human pair. The bottleneck got so small that it was just two people – Adam and Eve – and if you then imagine accelerated rates of mutation which would be either by divine intervention or just naturally, like the sheep on Haute Island, then that is entirely consistent with the evidence that we have today.
In order to understand why Craig is mistaken, we will have to understand exactly what heterozygosity is, how it relates to genetic diversity, and how natural selection has shaped it over time in the Kerguelen mouflon population. In tomorrow’s post, we will start with these key issues.
It is rare, but in this case, I agree with Answers in Genesis’ argument that pretty much everyone who talked on the subject of Adam and Eve talked about them as if they were actual people who really existed.
At some point, when discussing this topic, we have to stop having science overrule, instead of work together, with our theology. Otherwise, we agree with those that say that Judeo-Christian viewpoints are useless when discussing the origins of much of anything.
If we believe in a deity that can perform the miraculous, as much of the Bible presents, purely naturalistic studies, such as genetics, by themselves will not explain what we’re finding.
We may be sheep in the language of Scripture when talking about our behavior, but that’s where the comparison should, in my opinion, stop.
Thanks for the comment. One thing to keep in mind is that the scientific data do not tell us whether Adam and Eve were historical individuals - what the data show us is that the human race comes from a population. There are some scholars (for example John Walton) who accept the genetic evidence and also hold that Adam and Eve are historical. John views Adam and Eve as selected representatives from a larger population. Scientific evidence from genetics is very useful for answering certain questions (do we come from a population or a pair?) but unable to answer others (are Adam and Eve historical individuals?). One of the things I find annoying in this conversation is when some scholars claim that “the genetics precludes holding to a historical Adam and Eve.” It does preclude holding to Adam and Eve as the sole genetic progenitors of the entire human race, yes, but beyond that science cannot say more. The decision over Adam and Eve’s historicity is made using theological and hermeneutical methods, not scientific ones.
Also, I very much feel that science should work together with theology. I see science as a God-given activity to investigate the ordered creation that God has made. One of the reasons I accept evolution and population genetics is because I think God is not capricious but delights in ordaining and sustaining the world through ordered, consistent means. This provides the basis for investigating the created order with the tools of science, since the rules we observe one day will be the same the next day.
Thank you for this very informative series of articles on genetics. My last biology course was my freshman year in high school in 1962. A few things have been learned since then.
From what I get from today’s article, offspring inherit and pass on more than the particular genes they display. I suppose this would have to be, or a couple of generations of inbreeding would result in a population of identical twins.
A natural bottleneck in a population would have resulted from generations of dwindling population, where the 2 original sheep would have started with the genetic diversity of their breed. As an introduced species, presumably being under the care of humans, there would been no evolutionary pressure on the sheep population, and 65 years is not very long on an evolutionary timescale.
I am always amazed at how convincing ID and creationist “science” claims sound, and how easy for a real scientist to refute. If God created all of nature, why don’t people believe he created natural law also?
My suspicion has long been, regarding Adam and Eve, that the “image of God” that they were created in was more spiritual than physical. This would not be in opposition to the idea that other human beings existed in the same physical form.
What of the idea that Adam and Eve were specially, individually created? I don’t know that genetics would enlighten that at all. It seems like a claim that can only be made, but not verified.
I don’t understand what it means in evolutionary terms for human beings to start from a large population. The distinction apelike progenitor and human may be arbitrary according to evolutionists, but one is required to define human beings, and apelike progenitor, or one cannot use the names human and apelike progenitor of humans.
Once it is defined what is human, then there is by definition a first human being, and in evolutionary terms, that would most likely be a single human being, unless there are twins.
Possibly then the descendent of this human would be apelike again, but gradually the population becomes human.
And if you like order then why not look to the mathematical ordering of the DNA system which is exactly the same as that of the physical universe. (Peter Rowlands, Vanessa Hill, etc. who are evolutionists as far as I know) That’s science which is likeable. Understandable, simple, straightforward, pure mathematics, makes sense.
The problem with your line of thinking is that any definition you use from the scientific side of things is going to be arbitrary. It’s like saying, “there has to be a first day that you’re an adult”. And if there was a larger population at the time, any arbitrary definition you pick (say, a certain range of DNA), would apply to all of that population (unless you got really arbitrary). So what you have from the genetics perspective is a population gradually becoming human. We can pick the individuals 1 million years ago and say they were not homo sapiens; and pick the individuals 20,000 years ago and say they were; but there is a fuzzy area in between there.
You might go the theological route instead and say, the first humans were those whom God breathed his breath into. If that was just 2, then you have the problem of how that image of God spread to the others who existed at the time. Or you might say that God breathed his breath into all of the homo sapiens population at the same time–and again, that means there wasn’t a first.
Jim, I believe you have focused squarely on the problem that has produced such a lively discussion in the previous blogs: evolution provides a good explanation of a gradual development of the Homo sapiens species (represented by the Omo specimens of 190,000 BP) and of modern humans being present 20,000 yrs. ago–but there is a fuzzy area in between. The evidence for The Great Leap Forward indicates that the behavior which makes us truly human spread much more rapidly than could have occurred though sexual generation, even if that changed behavior had outstanding survival value. Let’s assume that the image of God breathing ‘true humanity’ into a life form ready to receive it was actually a sort of ‘programming’ of the potential ‘computer hardware’ that was the Homo sapiens brain–turning it into Mind. This Mind was capable of inventing a symbolic language that could then ‘program’ the brains of other Homo sapiens, spreading true humanity male-to-male, female-to-female, even child-to-adult. The mechanism for this "initial programming* is unknown at present, but the present size of the Homo sapiens brain is capable of forming far more interconnections than the largest IBM computer. So the mechanism is not dependent upon a favorable mutation.
The Nobelist, Christian de Duve puts it in terms of re-wiring the brain epigenetically. In this sense he states: “epigenetics designates a new kind of genetics involving transmissible traits that are not encoded in DNA sequences but accompany the DNA.” Further: “Only the general features of the brain are genetically determined. Its detailed wiring is superimposed upon the genetic blueprint; it is epigenetic.” And "(This) has been elucidated by the investigations of Changeux in France and Edelman in the U.S. According to these scientists, growing neurons continually send out projections in all directions. Acting like “feelers”, these projections, upon chance encounters with each other, form transient connections that quickly come apart again if they are not used."“The human brain is shaped to a large extent by the impulses to which it is exposed during the first years after birth, even, perhaps,while in the womb.” Of course this just gives a biological basis for the old wisdom “as the twig is bent, so grows the tree.”
Certainly this does not give scientific support for a historical A&E, but neither does science absolutely rule it out. If one believes that this belief is an important part of revelation and Faith, there is no reason currently to abandon it.
Al Leo
There is no fuzzy area in between in darwinism it is all fuzziness. All gradual, into infinity. You just have to define terms. Although I can see that if you define terms too strictly maybe some handicapped are then not termed human beings.
Joao, why don’t you read Tattersall’s “Becoming Human”, “Masters of the Planet”, and “The Case of the Rickety CossacK”. Tattersall is the most widely respected scientist in the area of human origins. How about Jared Diamond’s “The Third Chimpanzee”, or Simon Morris’ Crucible of Creation"–you surely have read those, and you know I have cited them. And Christian de Duve in “The Genetics of Original Sin” mentions The Great Leap Forward (although he does not give it the importance it deserves).
Why do you say I don 't cite any evidence? And to ask why I “want to stuff an omnipotent God into a tiny box” is totally off the mark. I firmly believe that God accomplishes His purposes for creation through the laws and methods He initiated at the moment of creation. This is what makes science so much fun. As far as we know, we are the only creatures who are trying to find out how He does it. If you have not perceived this from my responses, either you have some agenda which keeps you from understanding what I write, or else I am a miserably poor communicator.
Al Leo
Mohammad, you have hit on a subject that needs careful consideration lest it be misunderstood. Does God measure our value by our I.Q., or by the degrees we can cite after our names? Obviously NOT. In some way (which I sense, but do not fully understand) God values the potential in all of his creation. He values the potential in each human sperm and egg, but He must value more a zygote that is on its way to become a human being. He must value a human baby, regardless of whether the doctor pronounces it ‘perfect’ or whether it has Down’s syndrome. In His plan each of us has a potential to fulfill, and, if we struggle as best we can to fulfill it, we hope that is pleasing to Him.
My aunt Rose had 10 healthy children, and when the 11th was born with Downs, she was devastated, thinking she must have displeased God in some way. But as Tim grew up everyone could see that he was a delightful human being. And after she was widowed, Tim provided her with much needed support. I don’t know all of the purposes God had in mind in creating Tim, but he surely provided me with a needed lesson: Don’t judge a person as unfortunate from outward appearance.
Al Leo
[quote=“aleo, post:14, topic:2467”]
Joao, why don’t you read Tattersall’s “Becoming Human”, “Masters of the Planet”, and “The Case of the Rickety CossacK”. Tattersall is the most widely respected scientist in the area of human origins.[/quote]
Because I’m more interested in evidence than hearsay!
I read (and by that I mean mostly examining the figures and tables) highly relevant things like this:
Science 14 August 2015:
Vol. 349 no. 6249 pp. 734-738
DOI: 10.1126/science.aab1058
The developmental dynamics of marmoset monkey vocal production
They’re all hearsay. How long will it take before you will find out about those vocalisation experiments, and their relevance to human evolution, in a book? Five years?
Because you only cite what people say about the evidence, Al. There’s a difference.
If you’re not trying to stuff God into ever-smaller gaps, then I apologise and retract my statement. I made it because you convey a lot of enthusiasm for gaps.
I agree. And science is about the evidence, not what someone says about the evidence in a book, no matter how well-written.
We should be discussing the evidence itself, unfiltered through any pseudoscientific hearsay. That’s what both science and listening to God are about.
That’s why the good people here at Biologos spend so much time presenting the evidence and providing citations that allow you to learn far more about what God is telling us about His creation–but I’ll bet not a one of the denialists here are willing to look with his/her own eyes. They’ll go on and on about words.
I observe insanely mighty efforts by evolution denialists to reduce everything to hearsay to present a false equivalence between science and pseudoscience. All of their verbal gymnastics suggest that their motivation is that they lack sufficient faith to examine the evidence for themselves and are afraid that God is showing them something different from what people are telling them.
Is that what you are trying to do, John?
Do you see the parallel with your offering a blatantly-altered Bible translation that inserted a word not at all present in the Hebrew original to create a better fit with right-wing politics?
[quote=“Eddie, post:16, topic:2467”]
But it would be interesting to hear from Joao what he conceives “the BioLogos position” on God and evolution to be.[/quote]
To me, the Biologos position is that evolution is God’s chosen mechanism for creation.
Speaking for myself only, that means that Christians don’t have to close our eyes and pretend the evidence isn’t there, or is just hearsay. I view that stance as spiritual cowardice and absence of real faith.
Christians don’t have to pretend that science is just as (or even almost as, Christy) subjective as other ways of knowing by pretending that it has nothing to do with hypothesis testing–your favourite trope, in which the important scientists debate the same pile of evidence that is mysteriously produced by some inferior caste of scientists. Of course, the notion that they are sifting the same evidence is objectively false, as evolution denialists always ignore–or lie about–vast amounts of (or the most important pieces of) evidence.
In the real world, the best scientists produce the best evidence by testing their own hypotheses. Theorists are rare and typically work closely with empiricists. Theorists that don’t still view their jobs as advancing hypotheses that make empirical predictions.
[quote]Jon Garvey and I have been trying to find out what it is for a few years now, without success.
[/quote]I wouldn’t describe your efforts in that way at all.
You use lots of verbal gymnastics yourself, Joao. And you will also be filtering the evidence through your own perspective, which, as soon as the words of your thoughts leave your mouth, means that your own words will be hearsay, by your own definition.
It is unavoidable to have a perspective.
You give a good example of that by “interpreting”
What evidence do you have of that… yet you are unafraid to draw the conclusion…
It is interesting how absolutely little evidence you actually present yourself, while demanding that everyone else subjects their evidence (and interpretation thereof) to your inspection. Why not set a good example first?
Dear Joao,
does your reply improve the conversation in some way?
Be kind to your fellow community members.
Constructive criticism is welcome, but criticize ideas, not people.
It would be good to remember the community guidelines every time one writes a comment. It seems that you are off the topic. What evidence are you talking about?
Please be specific, so that one can respond to your doubts.
Who decides, who is in the inferior cast, and who is superior? The best scientists, in my view, are the ones, who best describe the laws of nature, not who prove their own hypothesis. We as human beings do not invent nature. Nature, the laws of the universe, was existing long before our creation. We are just blessed, to be able to approximate rules to understand this laws, using tools like math. I will quote some inferior scientists, according to your understanding:
1.“The first drink from the cup of natural science brings atheism, but at the bottom of the cup waits
God.” – Werner Heisenberg (1901-1976)
2. “Religion without science is lame, science without religion is blind.” – Albert Einstein (1879-1955)
3. “All matter originates and exists only by virtue of a force which brings the particles of the atom to
vibration. I must assume behind this force the existence of a conscious and intelligent mind. This mind
is the matrix of all matter.” – Max Planck (1858-1947)
4. “Man’s chief end is to glorify God and to enjoy him for ever.” – James Clerk Maxwell (1831-1879)
ETC…a long list of scientist, who belong to the inferior cast.
The above quotations are from famous scientists, mostly physicists. In the opinion of Sir Peter
Medawar (1915-1987), one of the top biologists of the twentieth century, “Scientists as a class
are rationalists, at least in the limited sense of believing without qualification in the necessity of
reason… Young scientists must however never be tempted into mistaking the necessity of
reason for the sufficiency of reason. Rationalism falls short of answering the many simple and
childlike questions people like to ask: questions about origins and purposes such as are often
contemptuously dismissed as nonquestions or pseudoquestions, although people understand
them clearly enough and long to have the answers. These are intellectual pains that rationalists
– like bad physicians confronted by ailments they cannot diagnose or cure – are apt to dismiss as "imagination". It is not to rationalism that we look for answers to these simple questions
because rationalism chides the endeavour to look at all."
