First, I think we need to clarify a few things when it comes to the use of terms that one might hear thrown around when this issue is talked about. There have been several Christian scientists who deny the historicity of Adam and Eve because they claim that it "would be against all the genomics evidence that we’ve assembled over the last 20 years, so not likely at all..." (Dennis Venema, Trinity Western University) Some have flat out said that, "genetics convincingly shows that there was never a time when there were just two persons." (Darrel Falk and Kathryn Applegate, BioLogos) Francis Collins of the Human Genome Project says, "Adam and Eve as the literal first couple and ancestors of all humans do not fit the evidence." But what do they mean when they say, "genetics convincingly shows" or "against all genomics evidence"? What genetic evidence are they referring to? This is a very important question because a lot is riding on this evidence.
The problem with this generalized claim is that genetic evidence has four components to it. There are four types of DNA that gets lumped into the phrase "genetic evidence" and some of it makes the interpretation of Collins, Venema, et al. very uncertain (we will get to why that is below). The four types of DNA are as follows:
- Autosomal DNA -- This is the DNA that makes up most of your genome and is a random combination of both of your parent's DNA. Since this autosomal DNA (atDNA) is a random combination of your parent's DNA (and their's is a random combination of their parents, ad infinitum) everyone's is completely unique. (This may also be referred to as "nuclear DNA" but that term is less precise.) For a good explanation of this type of DNA see this video.
- Chromosomal DNA Types -- At the genetic level, what determines our sex is our chromosomes. Males have a X and a Y chromosome. Females have two X chromosomes. Each contains DNA:
- X Chromosomal DNA -- This is the DNA that makes up your X chromosome (X-c) that you get from your mother. It is a random combination of her two X chromosomes, so, like the autosomal DNA, it is unique, though it does not change as quickly as autosomal DNA. For a good explanation of this type of DNA see this video.
- Y Chromosomal DNA -- This is the DNA that makes up the male Y chromosome (Y-c) and it is only passed from fathers to sons. Since there is only one Y-c, there is no random recombination of genes so the only thing that can cause change in the Y-c is mutation. This means it often not unique and changes very, very slowly. For a good explanation of this type of DNA see this video.
- Mitochondrial DNA -- This final form of DNA comes from the mitochondrial of your cells and it only comes from your mother. Male or female, it does not matter, your mitochondrial DNA (mtDNA) only comes from your mother. So, like the Y-c, there is no recombination of genes so the only thing that can cause change in the mtDNA is mutation. This also means, like the Y-c, it is often not unique and changes very, very slowly. For a good explanation of this type of DNA see this video.
Another term that gets used by scientists that often confuses people is "human". Now, you might think should be simple but it is not. An evolutionary biologist will use the term "human" to refer to any type of hominid from the homo genus like homo erectus or homo rudolfensis, not just homo sapiens (the taxonomic name for what species you and I are). This confuses the matter because scientists may refer to an ancient "human" fossil, footprint, or gene and they may not be referring to our species at all. This term also gives rise to the phrase "ancient modern human" used to refer to a homo sapien that lived in pre-historic times. This phrase not a contradiction in terms, but a further specification biologists use to refer to homo sapiens--a modern human species that lived long ago. I say this to make sure you aware of what is really being talked about when you read a science article in the popular news. If they say "human" they may not mean the species that you and I belong to and it may require more investigation on your part to figure out what they are really referring to. You can be sure that when I use the term "human" I mean a human like you and me, not any kind of animal that may have walked erect.
Second, we need to clarify that data that is being referred to by these scientists quoted above and that I will refer to below. There are two important types of data that come into play. The first I have already talked about in my previous post on this subject, and it is the mtDNA and Y-c data that shows that the entire human race can be traced back to one single mtDNA sequence for females and one Y-c sequence for males, a single pair of humans. (For a more detailed explanation of this see my first post on the subject.) As I just mentioned above, the mtDNA and Y-c change very slowly because the only mechanism for change is mutation. Therefore, scientist can trace the mutations of DNA take from all types of people throughout the globe back to a single first sequence for males and females. It is the single method of change--mutation--and the slow rate of change that makes this possible. (This would be impossible with atDNA, which is why it is important to know what kind of DNA someone is referring to!) The second type of data looks at the genetic diversity of humanity in the atDNA in humans. This data is drawn from mathematical models and attempts to take the present diversity of human atDNA and calculate how long it would take to get to the present state of diversity. These models have showed that in order for humanity to get to its present state of genetic diversity, it would have to have started out from a small population of humans (on the order of thousands) and not a single pair. These two sets of data appear to be in conflict, which is where our tale of two cases begins.
There are two possible ways of looking at this data. In these two interpretations different types of genetic data are given priority, which, again, is why it is important to know what genetic data someone is referring to when they say, "the genetic evidence says...".
Case #1 -- The Interpretation of Venema, Collins, et al.:
The mathematical modeling from the atDNA is given priority and it is assumed that humanity could not have originated from a single pair. This assumption is then imposed on the data that comes from the mtDNA and the Y-c. The question is then asked, "How could we have one ancient modern human mtDNA sequence and one Y-c sequence for all of us when humanity did not arise from a single pair?" Their answer is the "one lucky mother" hypothesis. They hold that there was originally thousands of mtDNA sequences and Y-c sequences in the first ancient modern humans but somewhere along the way all lines of these types of DNA died off except the one mtDNA and one Y-c that exist today in the present population. These sequences were from the "lucky" man and woman whose DNA was passed on while all other lines of DNA died out.
Case #2 -- The Biblical Interpretation:
In this case, the mtDNA and Y-c evidence is given priority because of the faults in the mathematical modeling and because of highly improbably "one lucky mother" hypothesis. In this case, the model is assumed to be incomplete (see below) and so it cannot be given the weight of mtDNA and Y-c tracking (which, remember, is a much slower process and much easier to trace backward). These ancient sequences are taken to actually point to a single man and single woman who were the progenitors of the entire human race. No special hypothesis is necessary for this interpretation, simply an acknowledgement of the limits of mathematical modeling with atDNA.
So, which of these cases seems more likely? It should be obvious by now that I choose case #2. Why? Well, I would like to expound upon the faults in the mathematical modeling and the "one lucky mother" hypothesis that I mentioned above:
- First, the mathematical models, while sophisticated, do not take into account very important data and therefore the results are unreliable. Remember, with atDNA, there is a random recombination of parental genes so there are many more things coming into play than just mutations--many things which the model leaves out. For one, it assumes that environmental factors do not drive genetic diversity. Environmental factors are things like location, food supply, isolation, diseases, and anything else that can drive a population to change. Recent studies (like this one: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1766376/) have shown this this is a dangerous assumption and can greatly skew the data. These models also assume monogamy throughout human history, and we all know that this is not a valid assumption. Now, before you think the scientists are just being sloppy, consider how difficult it would be to include these factors into a model. How many sexual partners do you assume each human has? How do you know what environmental pressures were on an ancient human population for which we have no historical record? You cannot and so these models cannot realistically include these things. However, this just goes to show that their results should be used with great reservation.
- Second, the "one lucky mother" hypothesis has a critical flaw in it. If one assumes that ancient humanity began with a small population of thousands, then for this hypothesis to work one has to find a catastrophic yet very selective mechanism that will kill off all genetic lines except for one male's and one female's. It must be catastrophic enough to kill off thousands of lines and all their progeny and yet it must also be selective enough to kill off all but one for the females and one for the males. What event or process could be so terrible that it would kill off all genetic lines and yet also so selective that it would leave one and only one genetic line for each sex? Even theorizing about such a mechanism is nearly impossible.
What would keep intelligent men like the ones mentioned above from acknowledging that case #2 is more likely the correct explanation of the data? Presuppositions. We must remember that all of us look at this data with our bias that we bring to the table. I look at the data having faith that what Scripture says is historical and theologically important and therefore I choose case #2. Theistic evolutionists, like the Christians mentioned above, look at the data already believing that evolution is a fact and therefore choose case #1 because it fits that presupposition better. Am I any different from them in this regard? No, I readily admit that my bias influences my decision, but the point is that case #2 is 1) an equally valid interpretation of the data and 2) fits the data well with fewer complications and less reliance on incomplete modeling.
Scripture is my highest priority and I make no apologies for that, but it is also true that the data itself does not go against Scripture. It actually fits quite well with Scripture. This is what we should expect if we truly believe that God is the author of all truth, whether it comes from the infallible authority of Scripture or the scientific realm. For, as Paul says in Romans 11:36, "from Him and through Him and to Him are all things. To Him be glory forever. Amen."
By His Grace,
Taylor
6 comments:
Factor in the flood, and you have an explanation for #1. Every line was killed off, of thousands, except that of Noah and his wife.
Good thought but you only take care of one line. You have an explanation for the male line, the Y-c, but not the female line. Noah and his sons shared the same Y-c but Noah's wife and his sons wives likely did not share mtDNA.
That would not help them anyway because 1) no evolutionist believes in a historical flood and 2) they would have an even greater problem with genetic diversity since the flood is later than creation and you have collapsed humanity back down to a population that is too small for their models.
By the way, it is good that you are thinking about the Flood because it does play a role in the genetics, just not the role a theistic evolutionist needs. See my first post, "Who Was Adam?" to see why the Flood reinforces case #2: http://a-short-saying.blogspot.com/2011/06/who-was-adam.html.
Great comment, Joshua, and you make a good point. Yes, an evolutionist would hold that natural selection and mutation gave rise to the first population of evolved humans, not a single pair. The rough story from an evolutionist's perspective would be that certain mutations occurred in a few hominids. They passed those on to their progeny (probably multiple children). Their progeny would pass them on and possibly introduce new mutations themselves. Then natural selection would weed out the harmful mutations and cause the helpful ones to spread. Eventually you could have a small populations of homo sapiens.
Now, I agree with you. It is not very probable because, as you say, you have to have many identical mutations in many hominids for natural selection to work with. Yet, that is the story that an evolutionist holds onto.
You forget that the the genetic evidence of Y-chromosomal Adam and Mitochondrial Eve didn't live within 50,000 years of each other.
You get past this by claiming the humans with the mtDNA of this Eve but without the Y-chromosome of Adam weren't really humans.
However, you would have to then assume the other hominid groups with the same mtDNA mutations were just decoys planted by God to confuse us.
Occam's Razor only applies when you look at all of the evidence, not the selective evidence you chose to look at.
Steven, please take the time to read my first post on the subject before you accuse me of being selective. It is referenced several times in the above post, to see for more information, and if you follow those links you will find I address the very time discrepency you mention and show how the biblical evidence accounts for it and even indirectly predicts it. It does not need any reference to hominids to be explained.
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