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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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BenYachov - #9606

April 13th 2010

>Before I buy a book, I first read reviews of it, and then decide. Having read the reviews of Feser’s book, I would most certainly not buy it or even read it. (Look at his “science”, for crying out loud!)

I reply:  Accept unlike you I wouldn’t rely on some anonymous fundie (be they religious or Atheist) I would read a professonal review.  For example Atheist philosopher Thomas Nagel said Dawkins criticisms of Aquinas where beyond amateurish & when I read Dawkins GOD DELUSION in the library I agreed.

Feser’s former Atheist professor at College praised his book.  So what’s your damage?


BenYachov - #9607

April 13th 2010

>If you think I do not know the difference between physics and metaphysics, you have not paid attention what I wrote before.

I reply: I have payed attention & u clearly don’t know what you are talking about.  I honestly believe you equate Metaphysics with the Occult or something.  I equate it using the classic definition of the ancient greek philosophers.  That which is beyond physics.  the study of being.  It’s not hard.


Savage - #9610

April 13th 2010

“You cited Camus before?  Like most Existentialists(be they Atheists or Theists) he was a notorious anti-rationalist.”

Anti-rationalist? According to BenYachov? But Feser’s science is rational. Now I ask you.

“The thing that breaks my heart is not so much you deny God savage.  But you deny the very reason, logic & sciences you claimed to have adopted in His place.  Thus in the end you have nothing.”

Science and religion is incompatible, because the former’s method is doubt, empirical testing, and the rejection of ideas for which there is no evidence.  There would be no religion in a short span of time if religious people practiced their faith using those principles. That is why I am an atheist; no proof of any god(s) around.  I have a full life NOW and don’t waste time thinking of an afterlife that does not exist.

BTW, I see the definition according the wisdom of BenYachov differs substantially from us mere mortals.


BenYachov - #9611

April 13th 2010

>You are caught in a philosophical “school” where you don’t think for yourself, and thus come up with scientific nonsense like these.

I reply:  First there is your hypocrisy, you accuse me of not thinking for myself then when I turn your irrational argument back on you & say the same of you, you complain about “name-calling”.  Typical New Atheist hypocrisy you can dish it out but you can’t take it.  Second you said “the philosopher and the scientist have totally separate operating fields;” yet what I wrote in post #9546 wasn’t a scientific statement but a philosophical metaphysical statement & yet above you called it “Scientific”(even thought we where discussing a book on Aristotelian philosophy by Feser)?  Thus how can I or anybody else believe you when you claim to know the difference.  This empirical proof you either don’t know what you are talking about or u are disingenuous.  so which is it?


BenYachov - #9612

April 13th 2010

>Anti-rationalist? According to BenYachov? But Feser’s science is rational. Now I ask you.

I reply;  Look it up buddy it’s not hard.
http://en.wikipedia.org/wiki/Existentialism
QUOTE"Emphasizing action, freedom, and decision as fundamental, existentialists oppose themselves to rationalism and positivism.“END QUOTE

Could you be more ignorant?  I wouldn’t so much mind except at this point I believe it to be willful on your part.


BenYachov - #9614

April 13th 2010

>Science and religion is incompatible, because the former’s method is doubt, empirical testing, and the rejection of ideas for which there is no evidence.

I reply: Again you are proverbially pleading the undeniable success of microscopes & ignoring the category mistake you are making in claiming they can’t detect the existence of Galaxies & thus concluding Galaxies must not exist otherwise you could see them under your microscope.  I’ve explained this & U have no rational response.

.


BenYachov - #9615

April 13th 2010

>There would be no religion in a short span of time if religious people practiced their faith using those principles.

I reply: Unless they ask the inconvenient question “If I should only believe in what can be empirically tested how can I prove this very concept true empirically?  If I can’t then doesn’t that mean this former is false by it’s own standards”?(short answer yeh)

AJ Flew abandoned the above incoherent positivist philosophy during the height of his Atheism because he was enough of a logical thinker to see it was just self-contradictory crap.  It’s not hard buddy.


BenYachov - #9616

April 13th 2010

BTW Feser wrote a book on Aristotelian philosophy not empirical science.  Stop confusing the two it makes you look thick.


David T. - #10002

April 16th 2010

Whoa everybody. I REALLY don’t see how you can grapple with the implications of this research on the Biblical Adam, without first dealing with what it means for the Biblical Noah. YECs understand the connection (Biblically and scientifically) between the creation and the flood, and any OEC or TE advocate must deal with it as well.
Assuming the flood was local for purposes of this discussion, it appears that the consensus seems to be that God “promoted” a hominid couple to human status by breathing into them spiritual life. Biologically, they would have been no different from their non-spirited hominid contemporaries. So we would not expect genetics to point to a bottleneck in this situation, would we?
Being spiritual beings, any offspring of theirs, even if by a non-spirited hominid, would be spiritual by virtue of having a spirited parent.
continuing…


David T. - #10004

April 16th 2010

...continuing…
The disappearance of non-spirited hominids would have been natural selection at its finest. Negatively, spirited hominids (humans) could have, over time, disassociated with them to the point where they were regarded as mere animals, and hunted into extinction. Positively, the non-spirited hominids would have selectively ended their specific existence by only seeking to breed with spirited humans. A third possible solution is found in Gen 6 and the flood account whereby the “sons of god” took the daughters of men. These “sons of god” could be a remaining hominid population corrupted by Satan, wiped out in the flood.
Again, the bigger question here is Noah, not Adam.


Aaron - #40472

November 18th 2010

Can anyone help me understand the Method II answer?

If Alu repeats are randomly inserted - and they continue to be inserted at the rate of 1 new Alu per 200 births - why would you expect that all the offspring of Adam and Eve would have the same Alu repeats at the same locations?

From the text:
“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”

I don’t see how that logically follows.  Why would you assume that Adam and Eve had any Alu repeats?  Perhaps they only had one or two?  If Alu’s keep being added to the human genome at random, shouldn’t we expect random distribution amongst the population no matter how large or small the initial population was?

Help me see the logic…


Kenny - #40961

November 20th 2010

From an old-earth (DayAge) creation perspective, the bottleneck would have happened at the flood. A literal old-earth view can see genetic changes occurring after the flood, because the ages at death began dropping.

Noah had three sons, each with a wife. That means 12 possible differences per gene to start. The ages at birth were greatly reduced, which may indicate that man began to multiply as God had commanded. This would mean a population explosion, especially if the individuals were living as long as indicated by the text. The older parents are when reproducing, the more likely it is that they will pass on mutations. They had many children late in life. 

Everyone seems to have lived in one general area until Babel. Then Ham’s descendants seem to go towards Africa, and Japheth and Shem’s seem to go northward. It seems to me that what is being measured is the population at the time when God scattered man. You are not measuring the population at the time when Adam and Eve were created, but shortly after the bottleneck (flood).

This scattering seems to also explain why non-Africans seem to have Neanderthal DNA, but Africans do not. Most of Ham’s descendants never met (committed bestiality with) Neanderthals.


Aaron - #41531

November 27th 2010

Hi Kenny,

I don’t know if you were trying to answer my question or just posting your opinions.

Why don’t you think Neanderthals were “fully human”?


TozerBGood - #66758

December 22nd 2011

Possibly explained in Genesis, before the flood, the Sons of God lay with the Daughters of men.


iceclimbr - #45591

January 1st 2011

The simplest answer is that there is no god.


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