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 Fellow of Biology for The BioLogos Foundation and associate professor of biology at Trinity Western University in Langley, British Columbia. His research is focused on the genetics of pattern formation and signalling.
Darrel Falk is former president of The BioLogos Foundation. He transitioned into Christian higher education 25 years ago and has given numerous talks about the relationship between science and faith at many universities and seminaries. He is the author of Coming to Peace with Science.

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BenYachov(Jim Scott 4th) - #9252

April 9th 2010

>It is possible to believe anything, but science functions on experiment to supply proof. All religions function on a belief system that requires no proof, thus their incompatibility with science.

I reply: Yours is the philosophical view know as “Scientism” which itself cannot be proven scientifically & thus is logically false according to it’s own standards or at best trivially true.
Also your definition of “religion” is incompatible with the Thomistic definition & is thus meaningless to me.  Aquinas said “Reason proceeds faith.  One must have reason to believe & a motivation for belief.”  I think your thinking of the definition of Fideism not religion which is anathema to Vatican One.

Blinded by Scientism
part one: 
http://www.thepublicdiscourse.com/2010/03/1174
part two
http://www.thepublicdiscourse.com/2010/03/1184

>is just a philosophical thought and supplies no argument.

I reply: Just like you QUOTE"And you want to reconcile science and religion? No chance.“END QUOTE

http://edwardfeser.blogspot.com/2010/04/nothing-but.html

Of course it can be defended if you follow the links, the argument & are not afraid to be challenged by new ideas or rational thinking.


Savage - #9256

April 9th 2010

“Yours is the philosophical view know as “Scientism” which itself cannot be proven scientifically & thus is logically false according to it’s own standards or at best trivially true.”

You have it totally wrong; I have no philosophical view of science except that I can see that science describes Nature. If the forces of Nature is harnessed correctly, humankind can go to Moon and back. The forces of Nature can be proved time and again. In everyday life the application of the forces of Nature results in our modern lifestyle. Religion is based on faith, not on proof. That is why science and religion are incompatible. No matter what philosophical arguments you use will show the contrary, be it deism, theism, Thomism, or any other -ism. It is just a matter of time before science will cut the taproot of religion.


BenYachov - #9277

April 9th 2010

>You have it totally wrong; I have no philosophical view of science except that I can see
that science describes Nature.

I reply:  That doesn’t logically follow & is self-evidently incorrect.  QUOTE"The forces of
Nature can be proved time and again.” Proven how?  Empirically? Conceptionally? Inference?
Metaphysically? Philosophically?  If you say “empirically” & contrast is with the
metaphysical claims of religion(which categorically can’t really be proven empirically) &
claim there is no “proof” for religion you are in fact making a philosophical claim that is
based on Scientism.  You are just like the confused Protestant who says “I don’t believe in
Sola Scriptura.  I just believe there is no other religious authority besides the Bible”. 
Which is of course the same thing.


BenYachov - #9283

April 9th 2010

BTW I believe natural science describes nature so your belief is unremarkable and does not logically lead to the conclusion “science and religion are incompatible”.  QUOTE"Religion is based on faith, not on proof. ”  Likely you mean empirical proof which is a claim made by the advocates of scientism who naturally believe this positivist incoherent fantasy in spite of the brute fact the concept itself cannot be proven empirically thus is still false by it’s own standards.

Sorry but your response to me is akin to saying the Andromeda Galaxy doesn’t exist because you can’t observe it under your microscope & no matter how many times it’ s explained to you Andromeda is a macro object & not a micro one you merely plead the undeniable success of microscopes in detecting microscopic objects & ignore the obvious category mistake on your part.
It’s the same with your scientism fallacy.  I suggest before responding to me you read the Blinded by Scientism links above otherwise I predict you will just talk past me & waste both out time.


Bilbo - #9325

April 9th 2010

Hi Savage,

Yes it is possible that both A1 and A2 evolved, and it is also possible that one group remained in stasis while the other group evolved.  Either way, there will come a point in time when a mutation occurs to one individual (and maybe its siblings) that makes that individual unable to reproduce with the other group.  At that point we have the potential fora new species.  If that individual’s mutation becomes fixed in the population, then we do have a new species.  We can then look back and say that individual was the first of a new species.


Bilbo - #9327

April 9th 2010

Hi pds,

This thread is about the question of whether the genetic evidence rules out the possibility of there being an Adam and Eve.  The additional question of whether they were the product of RM + NS or whether direct Divine intervention was involved is not the issue of this thread.


Glen Davidson - #9328

April 9th 2010

Either way, there will come a point in time when a mutation occurs to one individual (and maybe its siblings) that makes that individual unable to reproduce with the other group.  At that point we have the potential fora new species.  If that individual’s mutation becomes fixed in the population, then we do have a new species.

A species is not what cannot reproduce with the other group, it is what is genetically isolated due to subpar reproduction, through lack of mating opportunities (male or female does not respond to the mating calls, etc., of the other group), or for some other reason that is related to genetics and/or physiology (not just because they don’t ever encounter each other, that is).

Speciation might occur because an individual (this happens in plants occasionally) or group is unable to successfully reproduce with another group, like when a gene duplication event occurs in plants.  But that is not how a species is defined.

Glen Davidson
http://tinyurl.com/mxaa3p


unapologetic catholic - #9335

April 9th 2010

Bilbo, to demostrate why species are so “gray,” I refer you to this article about “ring species.”
http://en.wikipedia.org/wiki/Ring_species

As you can see, the two birds at opposite ends of the ring are of differnt species, but not different from the birds geograhically next to them.  You can’t select that exact point where you can say “species A is here and the next bird over is in species B.”

The same effect works historically with hominids.  The evolution from one species to another is so gradual that it is extremely difficult to identify when one species stops and another starts.  Same effect as seen in ring species except the graduations are temporal not geographic.


Bilbo - #9338

April 9th 2010

Hi Glen and UC,

Nothing that either of you said is relevant to my point.  Yes, one group might be able to breed with another, but doesn’t because of behavioral reasons.  We still define them as different species, and there was no doubt a first individual of one species that didn’t breed with the other.  Yes, there is ring species, geographically or temporally, but there still comes a definite point where one group cannot or will not breed with another.  And there would have been a first individual of the species where this happened.

Wake up, guys!  Unless you want to say that speciation happens when all the members of a group simultaneously undergo a change that makes them a new species, you must admit that there is always be just an individual (and possibly its siblings) that in retrospect was the first of a new species.

There is no genetic reason why there couldn’t have been an Adam and Eve.


Bilbo - #9339

April 9th 2010

oops…there will always be…


unapologetic catholic - #9340

April 9th 2010

Hi Bilbo;

Sorry,

This:

“...but there still comes a definite point where one group cannot or will not breed with another.  And there would have been a first individual of the species where this happened.”

is not true.  That’s our point.  There’s no bright line where you can say individual A is species Homo Habilis and his son is a Homo Sapiens.  All individuals within several generations of each other are in the same species and will be “fertile.”  You’ll have to pick indivudals separated by about 100,000 years to be able to say that one indidudal is in species A and another in B.

You seem to think that “species” is a Platonic Ideal.  It’s either black or white and fixed.  That’s not the way it works in biology.  Species are gray and very fuzzy.

Here’s one definition: “A group of organisms that shares an ancestor; a lineage that maintains its integrity with respect to other lineages through both time and space. At some point in the progress of such a group, some members may diverge from the main population and evolve into a subspecies, a process that eventually will lead to the formation of a new full species if isolation (geographical or ecological) is maintained.”


unaplogetic catholic - #9342

April 9th 2010

So,

In the absence of the gentic record we see,  “There is no genetic reason why there couldn’t have been an Adam and Eve” is true.

But, based on on the record we do have, the humans on this planet today did not all descend from a single pair.

And that’s all we can say.  I leave the theolgical considerations to others.


Savage - #9352

April 9th 2010

BenYachov, I read your links but did not comment on them because it is the usual philosophical drivel. Before you attempt (unsuccessfully, I must add) to put science in a religious or philosophical box, I would suggest you familiarise yourself as to the definition scientists have of science. Philosopher’s or the religiose opinion on science is immaterial to science.

Glen Davidson and unapologetic catholic, thanks for clarifying speciation and the concept “species” so well.


pds - #9376

April 10th 2010

Savage and Ben Yachov,

Daniel Dennett agrees with Ben Yachov:

“Scientists sometimes deceive themselves into thinking that philosophical ideas are only, at best, decorations or parasitic commentaries on the hard, objective triumphs of science, and that they themselves are immune to the confusions that philosophers devote their lives to dissolving. But there is no such thing as philosophy-free science, there is only science whose philosophical baggage is taken on board without examination.” Daniel Dennett, Darwin’s Dangerous Idea, 1995, p.21.


Bilbo - #9378

April 10th 2010

Hi UC,

Yes it may take a 100,000 years for the mutation to become fixed in the population, allowing us to say that there is a different species.  And by that time we would be unable to identify the original source of the mutation.  But there would still be an original source.  Again, the genetic evidence doesn’t rule out Adam and Eve.


BenYachov(Jim Scott 4th) - #9380

April 10th 2010

>I read your links but did not comment on them because it is the usual philosophical drivel.

I reply: Translation, you have no rational rejoinder so you are reduced to name calling.

>Before you attempt (unsuccessfully, I must add) to put science in a religious or philosophical box,

I Reply: This is an amazing level of anti-intellectualism & willful irrationality.  If you really bothered to read the links(& I’m skeptical at this point you did at best you likely skimmed them) Feser quotes ATHEIST scientists & philosophers to show the preminence of philosophy. 

>I would suggest you familiarise yourself as to the definition scientists have of science. Philosopher’s or the religiose opinion on science is immaterial to science.

I reply: So Bertrand Russell & E. A. Burtt(both cited in the article on Scientism) are not real scientists in the eyes of Savage.  Amazing!  Here we have the Atheist version of “Well they are not real Christians anyway so their opinion doesn’t count.” 

Scratch an Atheist find a fundamentalist.
P.S. Daniel Dennett is smarter than I thought.  Thought he’s no JLL Smart.


BenYachov(Jim Scott 4th) - #9381

April 10th 2010

Sorry that’s “J. J. C. Smart”.  My bad.  Anyway advice to aspiring non-fundamentalist Atheists out there.  Read Smart & throw away Dawkins if you wish to be successful in being polemical toward religion.  You will make few mistakes.


Savage - #9385

April 10th 2010

Daniel Dennett is a philosopher, and also a philosopher of science. I have quoted Richard Feynman before, but since you didn’t take notice, I’ll repeat his quote: “Philosophy of science is about as useful to scientists as ornithology is to birds.”

Dennett took on Roger Penrose, a mathematician, in his book “Darwin’s dangerous idea”, about a science he (Dennett) doesn’t understand. My point is simple: philosophers peck at the foundations of science without having first sharpened their numb wits on the very basics of science. (If you require examples, I’ll gladly give.) Russell was a very successful mathematician before he tried his hand at philosophy.

The laws of Nature described by scientists are universal. The laws of philosophy (analogy to Newton’s laws):  The First Law of Philosophy: For every philosopher, there exists an equal and opposite philosopher. The Second Law of Philosophy: They’re both wrong. ...


BenYachov(Jim Scott 4th) - #9388

April 10th 2010

>I would suggest you familiarise yourself as to the definition scientists have of science.

I reply: But how(according to Savage’s questionable “logic”) and by what objective criteria can we know if any individual qualifies as a “scientist” and is thus a reliable authority to define science for us?

In Savages’ weird world not Bertrand Russell, E. A. Burtt or Daniel Dennett would qualify as “scientists”.  This has powerful implications since by this definition no Darwinian can cite the arguments for evolution in “DARWIN’S DANGEROUS IDEA” since Dennett is not a scientist by Savage’s definition & that throw his views on adaptationism out the window.


BenYachov(Jim Scott 4th) - #9395

April 10th 2010

>I’ll repeat his quote: “Philosophy of science is about as useful to scientists as ornithology is to birds.”

I reply: If he mean in terms of determining or predicting empirical results then I would not disagree if however we are talking about interpreting the meaning of said results then he is as short sighted & irrational.

>The laws of Nature described by scientists are universal.

I reply: That’s a philosophical claim & not a scientific one.  You can’t escape philosophy & your Sola Scientifica Empirica dogma is tedious and irrational.

>The First Law of Philosophy: For every philosopher, there exists an equal and opposite philosopher. The Second Law of Philosophy: They’re both wrong. ...

I reply: Accept the above is not a scientific claim so by your own criteria it has no meaning & as a philosophical claim it is clearly a logical fallacy.


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