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) - #9400

April 10th 2010

>“Philosophy of science is about as useful to scientists as ornithology is to birds.”

I reply: OTOH what the above quote is really saying is scientists(according to Savage’s unstated ambiguous definitions ) are too stupid to understand philosophy just like birds are too stupid to understand ornithology.  This is pro-Science & pro-Scientist how?


BenYachov(Jim Scott 4th) - #9401

April 10th 2010

QUOTE"This saying is attributed to Richard Feynman (a scientist) and was apparently reasserted recently by Steven Weinberg (another scientist). If these men were simply identifying a problem with the way modern science has digressed, if they were in fact lamenting this
situation, well, that would be all well and good. But instead, both scientists seemed to be
approving of the fact that ‘scientists have no need of understanding the philosophy of
science.’ Regular readers of this blog will recognize the problem with this statement—
it’s…
That’s right! Self-refuting!

It’s very similar to my saying… “This game has absolutely no rules. Now here’s one…”

What these scientists are saying is,
  We scientists don’t bother with having a philosophy of science. And (oh, by the way),
that happens to be mine—my personal philosophy of science.
Absurd. Silly. A (fatal) mistake in critical thinking. And yet not only are these two Nobel
laureates guilty of this mistake, but the journalist quoting them also seems ignorant of the
problem here.“END QUOTE-Rick Gerhardt
http://antiochapologetics.blogspot.com/2007/12/philosophy-of-science.html


Savage - #9402

April 10th 2010

Perhaps I am too unkind to philosophers; two very true sayings by famous philosophers:

Bertrand Russell: “Science is what you know. Philosophy is what you don’t know.”


Cicero: “There is no statement so absurd that no philosopher will make.”


BenYachov(Jim Scott 4th) - #9404

April 10th 2010

“A text without a context is a pretext”. 
-unknown

Savage when you come up with a rational argument for your views do let us know. 

The New Atheist is just Fundamentalism without god belief.  It has all of it’s intellectual vices & practically none of it’s virtues.  Reason & logic are learned skills just because you deny god(s) doesn’t automatically make you rational.


Unaplogetic Catholic - #9417

April 10th 2010

Bilbo:

“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.”

Nope, speciaiton involves numerous mechanisms besides mutation.  A mutation happens to just one person and then may be inherited.  Itisi not true that those without that mutation are in a different species.  Lactoce toerance is a mutaiton that recently appeared in some humans.  It does not mean that those humans are a different species than those who lack that mutation.

“And by that time we would be unable to identify the original source of the mutation.”

Nope, again.  We can identify the source of a mutation pretty precisely.  That’s why DNA evidence is so good in paternity suits and criminal trials.


Argon - #9436

April 10th 2010

Why are we assuming that a new mutation is required immediately prior to genetic isolation or branching of a new species?  There are cases in plants where this occurs (multiploidy) but fertility can also be a gradient. In the latter case, the loss of intermediate compatibility factors (such as allelic variants) can eliminate fertility and gene flow between populations. In other words, the genetic variation necessary to block reproduction between isolated populations can already exist in the original populations prior to isolation.


Bilbo - #9444

April 10th 2010

Hi UC,

Yes, not all mutations lead to speciation.  But I believe it is assumed in biology that all speciation must involve mutation.

As for identifying the original individual?  Very unlikely.  Go back to my hypothetical case of needing 100 mutations to evolve species T from species S.  The first 99 mutations must already be fixed in the population.  Then an individual pops up with the 100th mutation.  The only way to identify that individual is to do so before that mutation becomes fixed in the population.  Afterwards, I doubt that it could be done.


Bilbo - #9445

April 10th 2010

Hi Argon,

Interesting idea, but does polyploidy occur in animals?  I wouldn’t know.


Savage - #9455

April 11th 2010

BenYachov

“The New Atheist is just Fundamentalism without god belief.  It has all of it’s intellectual vices & practically none of it’s virtues.”

If you herewith proclaim that the religiose are more moral than atheists, you are wrong. Read the independent scientific studies of Marc Hauser and Edward O Wilson.

“Driving our moral judgments is a universal moral grammar, a faculty of the mind that evolved over millions of years, to include a set of principles for building a range of possible moral systems.”  (Hauser)

Human morality is a result of our evolutionary history, and has nothing to do with religion. Just look how moral the Roman Catholic Priests have been through the centuries, and the tragic of it all is that the RCC leaders are protecting the perpetrators.


BenYachov - #9459

April 11th 2010

>If you herewith proclaim that the religiose are more moral than atheists, you are wrong. Read the independent scientific studies of Marc Hauser and Edward O Wilson.

I reply:  Sorry but Catholics shouldn’t make that claim since we believe God has written His Law into the hearts of Men & all men have the equal capacity for natural good regardless of their belief.  You really just have to accept the fact your boiler plate Fundamentalist Atheist polemics are really only effective with your fundamentalist counterparts in the religious community. (Yawn!)

>Human morality is a result of our evolutionary history, and has nothing to do with religion.

I reply: But since Catholics believe God can act threw secondary causes & providentially threw natural causes there is really no reason why we can’t believe God wrote His Law on the hearts of Men via the Evolutionary process.  In case you haven’t been paying attention I’ll repeat myself,  I am neither an ID advocate nor an opponent of Evolution so this “Evolution did it” Meme of yours is quite useless and a tad bit desperate.


BenYachov - #9460

April 11th 2010

>Just look how moral the Roman Catholic Priests have been through the centuries, and the tragic of it all is that the RCC leaders are protecting the perpetrators.

I reply: Ah yes the cheap shot, another tactic favored by your fundamentalist counterparts in the religious community accept they favor referring to the Inquisition but you should be given props for more modern thinking.  Well done.

Scratch an Atheist find a fundamentalist.  Yep.


BenYachov - #9461

April 11th 2010

BTW I should clarify, when I said Fundie Atheists didn’t have any of the virtues of the religious fundies I was referring to virtues like “Fear of God”, “respect for the teachings of Scripture”, “Faith in Jesus”, “a belief in natural Law.” etc

It would be kind of an oxymoron to complain “Atheists have just as much of a fear of God as religious people do blah blah blah….Hauser says so.”

Kind of defeats the whole rational doesn’t it?


Savage - #9468

April 11th 2010

“You really just have to accept the fact your boiler plate Fundamentalist Atheist polemics are really only effective with your fundamentalist counterparts in the religious community.”

Why? Where do you differ from the “fundamentalist counterparts in the religious community”?

“But since Catholics believe God can act threw secondary causes & providentially threw natural causes there is really no reason why we can’t believe God wrote His Law on the hearts of Men via the Evolutionary process.”

You believe. Great, where is your proof that my and others’ beliefs are wrong and you are right. Please don’t come with more philosophical drivel; supply just a shed of proof so we could at least advance forward on this topic.


BenYachov - #9482

April 11th 2010

>You believe. Great, where is your proof that my and others’ beliefs are wrong and you are right.

I reply: The above is a clear philosophical question(if ambiguous in specific content).  That’s it’s category.  Just like Andromeda is a clear macro physical object that can be detected by a macro detecting physical instrument like a telescope.  That’s it’s category. 

>Please don’t come with more philosophical drivel; supply just a shed of proof so we could at least advance forward on this topic.

I reply: So you are asking a philosophical question & forbidding that it be answered philosophically? Wow that really makes sense to you!  Me I’m stunned since it like me challenging you to prove Evolution is true without making an appeal to biological science or mechanistic philosophical presuppositions.  Like I said the New Atheism is nothing more than Fundamentalism without god belief.  It has all of it’s intellectual vices & practically none of it’s virtues.  Sad really.


Savage - #9494

April 11th 2010

“You can always pick up a copy of The Last Superstition by Feser, any of the writings of Ogdenberg or Ralph McInerny if you want to get an understanding of Thomism.”

Reading the literature on Thomism doesn’t mean it is true. You don’t grasp the point: science describes the forces of Nature whereas philosophy describes the thoughts of men and women, be they Plato’s, Aquinas’, Kant’s, or whoever. These thoughts and ideas change from person to person and you want to tell me Thomism is THE philosophy! You will only convince your brethren that you are correct but nobody else. Feser is just another philosopher who engages battle with philosophies he disagrees with.

When I ask for proof you call it philosophising. Have you seen the rigor proof of a mathematical theorem constitutes? That is what I mean. And you have just thrown more philosophical jargon at me instead of supplying any proof thereof.


BenYachov - #9498

April 11th 2010

Translation: “I am too threatened by any logical argument that goes against what I choose to believe so I will preemptively dismiss it without looking at it.” That is what u are really saying here Savage.  It is you who doesn’t grasp the point.  Philosophy is about the search for truth by means of rigorous rational analysis & logical argument. You keep asking metaphysical questions & you keep pretending they are scientific.  It’s unconvincing & Feser destroyed that view in one of the essays I linked too which you refused to read.  Can you formulate a rational logical argument as to why he was wrong?  So far I have little confidence you can.


BenYachov - #9499

April 11th 2010

Your dismissal of philosophy is as pathetic as any religious Fundie dismissing science because of competing & contradictory theories within it.  Philosophers do rigorous rational analysis of any argument just as scientists do more hypothesis & experimentation.  It’s all quite a logical & rational process.  Unlike your weird self-contradictory neo-positivist beliefs.  You forget there are a host of Atheists who disagree with your weird fundamentalist understanding of science(such as Dennett, Smart. Nagel, Oppy, Smith etc).  You can’t escape philosophy anymore than your religious counterpart can escape natural science.  Thought u both will clearly try by abandoning reason.  Have you seen the rigor of a philosophical formula?  It’s as complex & rational as any Mathematical formula(Oh & BTW Mathematics is not an Empirical Science so according to your weird Scientism dogma it’s not science since it’s not experimentally testable but uses logical analysis like Philosophy).


Savage - #9515

April 12th 2010

“Have you seen the rigor of a philosophical formula?”

No, that is what I am asking for all along. Give me these formulae and then with testing blind see if another person can come up with the same arguments and conclusions your philosopher did. You cannot supply them because they only exist in the head of a specific philosopher. Mathematics is the language science speaks in, and if you don’t understand the language, you will not understand science. And in this language wherein theorems are defined, scientific theories are formulated and where correctly implemented, enabled our modern lifestyle; electricity, the internet, modern transport, modern medicine; you could go on and on. I’ll ask again: what has philosophy contributed to modern life? Absolutely nothing!


Savage - #9516

April 12th 2010

I’ll leave you with a true word from a philosopher and Nobel laurite: “Prophecy functions on a very long term basis and has, as one of its properties, a characteristic which is the very source of strength of all religions: the impossibility of proof.” (Albert Camus.) I shall add philosophy to prophecy and religion.


Savage - #9518

April 12th 2010

Before wasting my time reading Feser’s book, I read a few critiques:

“This book was disappointing. I was expecting a robust defense of theism, but instead was subjected to the writer’s bigoted views and incessant juvenile name calling. If you do not agree with Edward Feser, then you are a lunatic, he tells us over and over.

“He confidently asserts that he will prove that God exists with absolute certainty. So he drags out three ancient arguments and tries a rehabilitation. His project is an utter failure.

“With high expectations due to the fawning reviews, I was taken aback by the lameness of the arguments, immature and unprofessional tone, and clumsy style.

“Don’t waste your time or money on this one.”


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