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Does Genetics Point to a Single Primal Couple?

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April 5, 2010 Tags: Human Origins

Today's entry was written by Dennis Venema and Darrel Falk. You can read more about what we believe here.

Does Genetics Point to a Single Primal Couple?

A Single Primal Couple?

Most Christians who have grappled with the science of genomics (the branch of biology that compares the DNA sequences of different organisms to one another) have done so with the question of common ancestry in mind: do humans share an ancestor with other forms of life, such as chimpanzees?

Here the evidence is very compelling, and reasonably accessible to non-specialists. For example, the human genome has numerous defective genes embedded it, and the vast majority of these defective genes are also present in the chimpanzee genome in the same relative positions with identical mutations. This sort of evidence is easily understood due to its qualitative nature.

A second question, and one that is less frequently explored even by Christians who accept common ancestry, is the issue of human/hominid population sizes during our evolutionary history. Specifically, is the human race descended from one ancestral pair in the recent past? Are we, as C.S. Lewis puts it in his Chronicles of Narnia, the “sons of Adam and daughters of Eve”? Is there genomic evidence to suggest that the human race is genetically derived from a primal pair? Here the evidence is more difficult for non-specialists to appreciate, because it is quantitative in nature.

Genomics can be used as an estimate of population sizes in the past by measuring genetic variation in the present. Genes come in different forms, or alleles: for example, the human ABO blood types are determined by three alleles of one gene. Some genes in human populations exist in hundreds of forms.

The catch, however, is that any individual person can only carry at most two different varieties of any one gene: one from mom, the other from dad. It therefore follows that a large population can pass on a large number of gene forms (alleles), but a population that passes through a population “bottleneck”—where only a small number individuals survive—will fail to pass on most of its genetic variation to future generations.

Attempting to square the Genesis account and common ancestry by positing a literal Adam and Eve who were the progenitors of the entire human race is, biologically speaking, looking for the most extreme population bottleneck a sexually reproducing species can experience: a reduction to one breeding pair.

Is there evidence that such a bottleneck has ever occurred? Dr. Peter Enns has been exploring whether this is even the right question to be asking from a biblical perspective (here, here, here, and here). Here we explore three independent ways of answering the question, this time from a biological point of view.

Method I:

The genetic consequences of a bottleneck required by a literal reading of Genesis 2-3 would be severe: at maximum, four gene-forms (two from each parent) would be passed on by Adam and Eve. Interbreeding in the (necessarily very small) population after the bottleneck would result in the further loss of some alleles due to chance alone. In short, the genetic impact of such an event would leave a stamp on the genome of that species that would persist for tens of thousands of generations as mutations slowly generated genetic diversity.

We can use this information, then, to estimate the minimum number of people that could have existed at any point in time. First we ask how many different alleles there are for a number of genes within the current population. Correcting for the rate at which we know new forms of genes appear (mutation), we can calculate the minimum number of people needed to generate the current amount of diversity. Numerous studies analyzing many different genes all point to a bottleneck. However, these studies are all clear: during the bottleneck, there were several thousand individuals, not two.

Method II:

In earlier posts, we have discussed the fact that DNA segments known as Alu repeats, can insert themselves at various locations the genome. It turns out that the Alu sequence comes in various forms, like different makes of cars—Fords, Toyota, etc. There are several thousand families of Alu.

Consider just one family, which we will call Ya5. Members of this family have been inserted into human chromosomes at 57 mapped locations. If all humans descended from a single pair of individuals, all humans would have each of the 57 elements in pretty much the same locations, since individual members of the family almost never move. However, the human population consists of groups of people who share some insertion points but not others. The multiple shared categories make it clear that although a human population bottleneck occurred, it was definitely never as small as two. In fact, this line of evidence also indicates that there were at least several thousand people when the population was at its smallest.

This method is much different than Method I since it does not depend upon mutation rate, but the answer is similar.

Method III:

A third independent estimate makes use of a concerted research effort called the HapMap project. Humans have 3 billion bits of information in their genomes. (The official term for one bit is a “nucleotide.”) The bits between any two individuals differ at many sites, which is, of course, why we don’t all look the same.

In the HapMap project, one million of these differences have been analyzed by examining something called linkage disequilibrium The technical details are beyond the scope of our discussion, but to give you a feeling for how it works, imagine that you have a gene for blue eyes and a gene for a bent finger, both of which you inherited from your dad. Assume these genes reside in the same “neighborhood” on chromosome 2. Because these genes are close to one another, chances are that if your brother got the blue eye allele from your dad, he would have received the bent finger allele as well. After all they are neighboring genes, both on chromosome 2. Why? Blocks of genes in the same neighborhood on a chromosome are usually inherited together. Alleles that are very close together on chromosomes tend to stay together for many generations before they are “mixed and matched” through a process called recombination.

Now pretend that someone analyzes both your DNA and that of your brother in a double blind experiment. The investigator would, upon examining the results, be able to say, “I’ll bet these two people are related to each other.” And he would be right.

Now picture being able to do this, not for two differences, but for a million differences all at once and not just for two people, but for many people from all over the world. Using this approach, it is possible to tell how many people gave rise to all the prevalent combinations of differences. In short, we can tell if everyone came from just two people at any time in the last 200,000 years. So did we?

No.

This third independent method tells us that everyone alive today is related, but not to a single pair of people. We are related to a population that consisted of several thousand people with their several thousand combinations of these million genetic differences.

Here’s the real point of this. When you have one way of doing a calculation and you get a certain answer, perhaps you are justified in being a little skeptical. Perhaps you made a mathematical mistake, or maybe you made a faulty assumption. However, when you do your calculation using two totally different approaches, using methods with completely different assumptions, and each method gives you the same answer, you become convinced it is correct. Three, of course is just icing on the cake.

So that’s the situation we are in with regard to the human population size in ancient history. There was a bottleneck. There were likely fewer people alive during that time than the number of fans attending a typical NHL hockey game. (We don’t know if they were all together in one village, of course, but the total was small.) However, it was not two people. Our species diverged as a population. The data are absolutely clear about that.

References:

  1. Relethford, JH. 1998. Genetics of modern human origins and diversity. Annu. Rev. Anthropol. 27: 1-23.
  2. Tenesa A, Navarro P, Hayes BJ, Duffy DL, Clarke GM, Goddard ME, Visscher PM. 2007. Recent human effective population size estimated from linkage disequilibrium. Genome Res. 17:520–526. (available free here)
  3. Sherry ST, Harpending HC, Batzer MA, Stoneking M. 1997. Alu evolution in human populations: using the coalescent to estimate effective population size. Genetics 147:1977-1982. (available free here)
  4. http://hapmap.ncbi.nlm.nih.gov/index.html.en

 

 


Dennis Venema is professor of biology at Trinity Western University in Langley, British Columbia. He holds a B.Sc. (with Honors) from the University of British Columbia (1996), and received his Ph.D. from the University of British Columbia in 2003. His research is focused on the genetics of pattern formation and signaling using the common fruit fly Drosophila melanogaster as a model organism. Dennis is a gifted thinker and writer on matters of science and faith, but also an award-winning biology teacher—he won the 2008 College Biology Teaching Award from the National Association of Biology Teachers. He and his family enjoy numerous outdoor activities that the Canadian Pacific coast region has to offer. Dennis writes regularly for the BioLogos Forum about the biological evidence for evolution.
Darrel Falk is former president of BioLogos and currently serves as BioLogos' Senior Advisor for Dialog. He is Professor of Biology, Emeritus at Point Loma Nazarene University and serves as Senior Fellow at The Colossian Forum. Falk is the author of Coming to Peace with Science.

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Dennis Venema - #8812

April 6th 2010

Hi Martin,

Even if one assumes that God did “tweak” the human genome, it doesn’t solve the “problem” of why the human genome looks the way it does, with all its hallmarks of common ancestry. Have you ever read Todd Wood’s paper on human / chimpanzee comparative genomics? Todd is a YEC and thus believes that humans were created de novo without any ancestors about 6,000 years ago. That belief doesn’t help him much as he struggles with the genomics evidence.

Here’s a direct link to a PDF of the paper. I’d love to know what you think of it. Best,

Dennis

http://documents.clubexpress.com/documents.ashx?key=u4FIU0eLuT6SmyXcvLmbCiFa4UnoWsTP3lyArVOo/gM=


BenYachov - #8814

April 6th 2010

When Faith and Reason Clash:
Evolution and the Bible

http://www.asa3.org/ASA/dialogues/Faith-reason/

Some heavy reading for you guys.  Plantinga’s argument, his critics, supporters & his responses with a last word from Hasker a critic.


BenYachov - #8817

April 6th 2010

Here is a thought.  In the Bible when Jesus miraculously caused Peter to catch a TON of fish, nationalistically he could have simply providentially caused all the fish in the area to swim into Peter’s nets.  He need not have created fish ex nihilo in the net since the NET was in the water at the time.  OTOH when Jesus miraculously multiplied fish and loafs of bread do we have to believe Angels went out & caught the fish & harvested wheat & ground it into bread then teleported the finished products to Jesus in time to feed the several thousand?  Or could Jesus have simply created ready made bread ex-nihilo without actually having harvested wheat?

Thus I am not so sure I consider “human / chimpanzee comparative genomics” based arguments & other arguments based on the similarities between human & animal DNA to be per say logically convincing & I don’t believe in YEC mind you.


BenYachov - #8822

April 6th 2010

edit"naturalistically”  NOT nationalistically.  Stupid spell check….....


Rich - #8836

April 6th 2010

Dennis (8799):

Sorry, but I don’t follow your argument.

If we can’t get at the Virgin Birth (2,000 years ago) scientifically, then how can we get at the Creation of Adam and Eve (6,000 years ago or more) scientifically?  Both are inaccessible, one-off miraculous events, to use your language.  We weren’t there in either case, and wouldn’t grasp the supernatural means used in either case.

You are saying that the Adam and Eve “event” would have left different traces in our genome than what we see.  But can this be determined from the rules of genetics alone, without any assumption that macroevolution has taken place?  If the argument presumes the truth of macroevolution, and all the genetic data is interpreted through the macroevolutionary filter, then the argument is circular, since it assumes just what the YECs (I’m not one, by the way) will not grant.  You can’t use genetics to prove evolution true, if the genetics you are using is already saturated in evolutionary theory.  Any arguments against Adam and Eve based on statements like “We know that this line diverged from this one at least 8 million years ago” already presuppose the truth of macroevolutionary theory, which is precisely the point at issue.


Rich - #8837

April 6th 2010

Ben Yachov (8817):

That’s “per se”, not “per say”, but I like your example of the fishes and the loaves.  I have never found a TE who will give me a straight answer about that story—did it happen as described or not?

This is the problem with TE, not that it accepts evolution (which I don’t see as theologically offensive in itself, as long as it’s understood to be guided or planned by God), but that it is squeamish about miracles generally, while claiming to be true to the teaching of the Bible about God’s action in the world.  Most TEs I have met are dubious about a large number (probably the majority) of Old Testament miracles, and appear to be cagey about several famous New Testament ones.  This puts them in a rather difficult argumentative position, i.e., of “picking and choosing” when God is allowed to interfere with nature, while accusing YECs and others of having a theology and a science inferior to their own.  Many of the great Christian scientists of the 17th and 18th centuries would have accepted all the Biblical miracles without batting an eye, so why the slipperiness from our modern Christian scientists?


Karl A - #8838

April 6th 2010

Rich (8836), I have just a few clarifying questions:
1) It seems you would concede the main point of the article (at least for sake of argument), that our ancestral population was always in the thousands, right?
2) Am I right in saying then that your question is whether God could have created A&E in a special miracle and placed them *alongside* our other ancestors, with whom A&E’s descendants would have then intermarried?
Because, we can’t get at the Virgin Birth genetically because Jesus left no descendants.  (And, contrary to Catholic teaching, there is no mention in the Gospels that Jesus’ brothers and sisters were also conceived “immaculately”.)  OTOH, we could get at A&E genetically (if they were “immaculately” created), unless (perhaps) they interbred with a larger existing population.  Even then I suppose we could look for some special “A&E genes”.


eddy - #8846

April 6th 2010

Obviously I believe that God has, and does, perform miracles.  I just don’t assume that he does them to make my scientific positions seem more credible than they actually are.

Arguing for contemporary science, this statement makes much sense from BioLogists.  Problems arise when somebody hoodwinks Christianity to fit with the current scientific understanding of the world or when somebody hoodwinks current science to fit with Christianity.

At the end of the day, we will be forced to define what is credible Science and what is credible Christianity.


Gordon J. Glover - #8853

April 6th 2010

Martin and Ritch,

Yes, God could have manipulated the genomes of all species to speed up genetic diversity—and that would make sense since the bottlenecks caused by a recent de novo creation and global flood would have severly limited our gene pools.  But to accept this ad hoc position, you must also believe that God miraculously redistributed all flora and fauna geographically to hide evidence of radiation from Mt Ararat, and that He miraculously planted fossil evidence and made it consistent both in the vertical (ie: superposition and biostratigraphy) and the horizontal (ie: biogeography and plate tectonics) to make it look like there actually were common ancestors who lived during the exact geologic ages that the evolutionary theory would predict.

But why would God go through so much trouble to invent and maintain such a consistent, but historically false, appearence of a scientific theory that (according to some) has no spiritually redeeming value?


Gregory - #8864

April 6th 2010

Rich wrote:
“This puts [TEs] in a rather difficult argumentative position, i.e., of “picking and choosing” when God is allowed to interfere with nature, while accusing YECs and others of having a theology and a science inferior to their own.  Many of the great Christian scientists of the 17th and 18th centuries would have accepted all the Biblical miracles without batting an eye, so why the slipperiness from our modern Christian scientists?”

For the sake of trying to focus on the views of the authors of the article, I’m pretty sure Falk believes in most Biblical miracles. I’m not sure about Venema. You ask him good questions (8836), Rich.

I attended a conference with biochemist/theologian A. Peacocke. An Orthodox priest raised the topic of miracles, to which Peacocke answered: I’d like to see more evidence (for them). He sounded like such a western objectivist! The priest just shrugged at him unimpressed.


Gregory - #8866

April 6th 2010

(cont’d)

What you say about TEs is interesting, in contrast to the meaning of ‘BioLogos’, which openly promotes ‘the language of God.’  Perhaps this is a good opportunity for BioLogos to show that it is less, as you say, “squeamish about miracles” than is TE.

BioLogos also less depends upon the concept ‘evolution,’ even the scientific part, than does TE, which wraps the science, ideology and philosophy of evolutionism into its worldview. Giberson has made crystal clear that this approach is problematic. As far as I can tell, “putting evolution in its proper place” is an important part of BioLogos’ ‘language of choice’...as well as ‘saving Darwin’.

BenYachov raises the issue of whether or not we can trust ‘the science of genomics’ if/when it contradicts *logic*. The field of genomics started in the 70s-80s. One can easily say it is not a *mature* science.

If genomics (and genomicians/genomicists?) *absolutely demands* biological polygenesis of human beings, this is a significant challenge to Jews, Christians and Muslims around the world for interpreting their sacred texts.


Dennis Venema - #8869

April 6th 2010

Greg, you can rest assured that I believe in Biblical miracles. Incarnation, Resurrection, Jesus’ healings, walking on water, etc etc. I also believe that the charisma are for today (speaking in tongues, prophecy, gifts of healings). I’ve even had the grace to have experienced a number of them. Denis Lamoureux and I are quite similar in that regard.

Best,

Dennis


pds - #8871

April 6th 2010

Martin #8803,

Thanks for your comments.  Since some have misinterpreted this kind of scenario to suggest that this would mean that God was deceiving us, I am reposting a scenario I mentioned earlier:

Does God heal?  What if a man prays that God will heal his wife’s breast cancer, and God responds by tweaking her BRCA genes?  What if the first humans lived 200,000 years ago, and God tweaked human genes once every 200 years to heal in answer to prayer?  That would mean 1000 changes to the human genes.  How would that affect our current calculations?  What if God intervened 5 times each year?  Now we are at a million changes.

If God does things out of his love, and there are SIDE EFFECTS that affect the human gene pool, God is not deceiving us.  We are deceiving ourselves by having too small an understanding of God and his work in history.  Job 38 is instructive as to the epistemology we should adopt.


pds - #8872

April 6th 2010

(cont.)

and this:

A better example would be a prayer of a dying woman to protect her daughter and her children from the breast cancer that had killed her mother, her aunt, and now her.  I think my basic point is clear: God might intervene in history to do something that might have a side effect of affecting the gene pool. 

Dennis and Darrel must rule such scenarios out for their conclusions to hold.  I find this to be completely unreasonable if we accept that there is an omnipotent and benevolent God whose love for humans is far greater that we can possibly imagine.


BenYachov - #8874

April 6th 2010

>(And, contrary to Catholic teaching, there is no mention in the Gospels that Jesus’ brothers and sisters were also conceived “immaculately”.)

I reply: Uh we Catholics (& Eastern Orthodox, the original Reformers and other near Eastern Churches) believe Jesus didn’t have ANY uterine brothers & sisters.  The “Brothers” & “Sisters” of Jesus mentioned in the Gospels are at best children of Joseph by a previous marriage or more likely cousins.
The Immaculate Conception is a doctrine that is unique to Mary(i.e our belief God applied the Redemption of Christ retroactively to her at her conception so she would be redeemed of Original Sin) and only she was redeemed in this fashion.  Jesus wasn’t “Immaculately Conceived” since that would imply Jesus redeemed himself which is contradictory and an oxymoron.  Jesus didn’t have original sin because of the nature of the Incarnation.  His human soul was hypostatically united to the Divine Nature & thus by definition his soul beheld the Beatific Vision & thus couldn’t by nature be in a state of original sin.  Just thought I’d clarify.


pds - #8875

April 6th 2010

Ben #8811,

I enjoyed this:

“Thus until the Pope tells me different I remain hopelessly a pseudo-Agnostic on the matter and remain hovering between Old Earth Creationism and Theistic Evolution and cheerfully laugh at the fundamentalists on all sides(including the TE’s) because I am such a self-satisfied git.”

I am glad you said it first.  Dennis and Darrel’s overconfidence in their conclusions also strikes me as a form of “fundamentalism.”  When Gordon called my suggestions “rediculous” (sic), it was icing on the cake.


pds - #8878

April 6th 2010

Gary #8790,

I am not sure that Gould uses the language you are using, but one discussion is in Wonderful Life p. 277 and following.

Dennis #8786,

That article is about much more than that.  It is about the inconsistencies in molecular and morphological phylogenies.  It goes to the confidence we can have in reconstructing the past based on molecular evidence.


BenYachov - #8879

April 6th 2010

Fundamentalism isn’t just for Christians, Muslims or YEC.  Even TE can be fundies too.


Dennis Venema - #8901

April 6th 2010

pds,

what part of that article do you think is relevant to vertebrate phylogenies, and why?

Dennis


Martin Rizley - #8920

April 6th 2010

Dr. Venema,
I took a look at Todd Wood’s paper; I found it interesting, despite my limited ability to comprehend the technical language involved.  What I appreciated was:  (1) his honesty in recognizing that there are hard questions for creationists to answer when it comes to explaining the patterns of genetic similarties between chimps and human beings, along with (2) his unwavering commitment to the authority of Scripture in what it teaches about the special creation of man and the diversity of original created ‘kinds’ that God made during the week of creation.  It seems to me that his approach to science is correct, for he is asking questions and pursuing answers within a presuppositional framework that affirms both the perspicuity and inerrant authority of Scripture in all that it teaches.  This a priori commitment, in my view, is what distinguishes a distinctively Christian approach to science from the prevailing secular approach to science that has captured our culture.


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