We continue our review of the book,, by Dennis Venema and Scot McKnight. Today, Chapter 3- Part 3
As Christians become increasingly familiar with the argument for common descent and begin to understand it, they, not unreasonably, begin to wonder where Adam fits in. Where in the phylogenic tree did the man Adam exist? As I hope you dear readers are starting to see, science is good at answering some questions (and sometimes good at raising more questions than it answers), it is simply unable to weigh in on the historicity of Adam and Eve as individuals. What science can conclude is that if they were historical, they were not the sole parents of all humanity, but part of a larger population. Beyond that, science cannot say.
When modern humans first arose in Africa about 200,000 years ago, there were other hominin species alive who had migrated out of Africa prior to our species coming into being. Homo erectus was already widespread in Africa and outside it. The ancestors of Neanderthals had left Africa at least 100,000 years before our species arose and had spread to the Middle East, Asia, and Europe. Modern humans left Africa in significant enough numbers to leave evidence of that migration about 50,000 years ago. The ones that stayed behind became the ancestors of present day sub-Saharan Africans, and the rest of us derive from that smaller emigrating group of an estimated 1,200 more or less. As they left, they encountered the other hominin species that had left previously.
What were the nature of those encounters? Well, since the advent of paleogenomics, we know that Neanderthal DNA is nearly identical to our own yet just outside the range of present day variation. They are our “kissin’ cousins”, and apparently some “kissin’” went on, if you know what I mean, and I think you do, as some modern humans have 1-4% of Neanderthal DNA in their genomes. As Dennis says:
“Of course, this raises the whole “species question” again: if humans and Neanderthals interbred, then aren’t we just members of the same species? Recall that attempting to demarcate species is and attempt to draw a line on what is in fact a continuous gradient. So we “sort of” are the same species, because we did interbreed to a limited extent, and some present-day members of our species, yours truly included, descend in part from Neanderthal stock. Are dogs, coyotes and wolves the same species or distinct? What about lions and tigers? It’s a similar question. As a species, then, we had to shift our Facebook relationship status to “it’s complicated” when it comes to Neanderthals.”
The recent discovery of the “Denisovans” complicates that relationship even further. The DNA sequencing on a specimen from the Denisova cave in Siberia revealed a hominin neither Neanderthal nor us. They share a more recent ancestor with Neanderthals then they do with any other species. Present-day humans of Asian and Oceanic descent inherit 3-5% of their DNA from the extinct Denisovans. Further, Denisovans contain DNA from yet another hominin species. Some speculate that might have been Homo erectus, but we’ve yet to find intact DNA from Homo erectus, so it remains speculation.
So, as Figure 3-7 shows, not only is hominin evolution a branching bush, but there are cross-connections as well. Sometime between 500,000 and 300,000 years ago, the common ancestral population of Neanderthals and Denisovans leave Africa, later splitting into two species. As humans leave Africa 50,000 years ago they encounter Neanderthals in the Middle East and breed with them. As this human population expands into Asia, they encounter Denisovans and interbreed with them. The result is that present-day sub-Saharan Africans lack Neanderthal or Denisovan DNA, Europeans have Neanderthal, but not Denisovan DNA, and Asian/Oceanic people have both. So what does this have to do with Adam and the Bible? Nothing, absolutely nothing, and that is the point. Obviously, the bible authors had no idea of any of this, nor could they even have imagined it, any more than they could have comprehended quantum theory or plate tectonics or space travel. So stop trying to CONCORD the scriptures with modern science, it simply can’t be done. Why not just take the point of the narrative as THE POINT God is inspiring the authors to make. The ancient understanding of science is BESIDE THE POINT.
When presenting genomic data to evangelical audiences, Dennis frequently gets questions about Mitochondrial Eve and sometimes Y-Chromosome Adam. Mitochondrial Eve is an ancestor to every living human, likewise Y-Chromosome Adam is an ancestor to every living male. Wait, what? If we descend from a population how can that be true? The answer is that they are both true. It has to do with how mitochondrial and Y-chromosome DNA are inherited.
Mitochondria are the components of a cell that performs energy conversion. The have their own genomes distinct from the usual chromosome set that are called nuclear genomes because they are found in the cell’s nucleus. In humans we have the nuclear genome consisting of 23 pairs from the mother and 23 pairs from the father and the mitochondrial genome. Mitochondria are passed down only through eggs, as a result this snippet of DNA is passed down only from mothers to their children, not from fathers.
Similarly, the Y-chromosome has its unique pattern of inheritance; from father to son, and only to sons, since inheriting a Y-chromosome determines the offspring will be male. These two forms of DNA, then, have a different pattern of inheritance from regular chromosomes, which can be passed on by either mothers or fathers to offspring of either gender.
Y-chromosomes hit a dead end if a male has only female offspring, and mitochondria hit a dead end if females have only male offspring. So if we examine a pedigree, as before, shown in Figure 3-8, we can now trace mitochondrial and Y-chromosome variation. We can see that the four children of generation III will inherit the mitochondrial DNA of their mother, who in turn inherited it from her mother (individual I-1). The four children have only one ancestor from generation I for their mitochondrial DNA: their maternal grandmother. Neither their maternal grandfather (I-2), paternal grandfather (I-3), nor paternal grandmother (I-4) contributes mitochondrial DNA to generation III. Similarly, the two boys in generation III have only one ancestor in generation I for their Y-chromosome; their paternal grandfather. The Y-chromosome of their maternal grandfather (I-2) has not been transmitted to generation III (nor II because this man had only daughters).
In contrast, you will recall that all four grandparents contributed regular chromosomal DNA to generation III, and that the DNA diversity in this generation requires at least four ancestors. These children descend uniquely from one man (for their Y-chromosome DNA), one women for their mitochondrial DNA, but at least 4 ancestors for their regular chromosomal DNA. This, in microcosm, is exactly why all humans can descend from one Mitochondrial Eve for our mitochondrial DNA, and one Y-Chromosome Adam for our Y-chromosome, and 10,000 other ancestors for our regular chromosomal DNA. Both mitochondrial DNA and Y-chromosome DNA are prone to being lost in a lineage over time because of their gender-specific inheritance patterns. The population bottlenecks that we passed through as species also likely contributed to the loss of many mitochondrial and Y-chromosome lineages. Regular chromosomal DNA, on the other hand, is much more resistant to loss because it can be passed down to offspring of either gender by parents of either gender. Y-chromosomes require and unbroken line of male ancestors; mitochondrial DNA requires an unbroken line of female ancestors; but regular chromosomes simply require an unbroken line of ancestors to be passed on. Dennis notes:
“Unfortunately, many antievolutionary organizations like to promote Mitochondrial Eve, and Y-Chromosome Adam without explaining these issue. Typically, it enough for them to state that they are respectively the common female ancestor for all women and the common male ancestor for all men, to claim (or merely imply) that these data are consistent with Adam and Eve being the SOLE parents of all humans, and to leave it at that. Thus, for their case to seem plausible, they count on their audience not completely understanding how these types of DNA are inherited—or perhaps they misunderstand it themselves.”
Of course, and especially since the 2011 cover article in Christianity Today, certain evangelical Christians have attempted to rebut the genomic evidence that humans descended from a population rather than a pair. Their attempts are mostly arm-waving appeals to “speculation” and “evolutionary assumptions” and have yet to rise to the level that actual genetic scientists take seriously. For example:
“Stephen Meyer, a Discovery Institute leader of the intelligent design movement, (claims that) Biologos leaders are using an unsubstantiated and controversial claim to urge pastors and theologians to jettison a straightforward reading of Genesis about the human race arising from one man and one woman. They think ‘the science’ requires such a reinterpretation, but apart from the speculative models that make numerous question-begging assumptions, the science does no such thing.”
Biologos has a number of series of posts that critique Meyer and allow him to respond. It’s a nice back and forth and non-acrimonious to boot, so kudos to both parties for not flaming each other. But as far as making a compelling case against the genomic science, Dennis again quotes young earth creationist scholar, Todd Wood:
“The population reconstructions are complex and not easily understood by lay-people right now. So creationist responses lag behind the current science, and the best your typical creationist can do is cast aspersion on the science. Until we have a creationist well-trained in modern theoretical population genetics, I think we will continue to have only unsatisfactory answer to these ancestral population reconstructions.”
Well, this is the point that Dennis ends the chapter. I know it was “eyes-glazing-over” technical, but, as someone commented recently, it can’t be helped; sometimes reality is complex. It is my opinion that before you can “pooh-pooh” the science, you have to at least make an effort to understand it based on what the scientists themselves say. In other words, don’t base your judgement on the science on “creationist” critique, read it for yourself. That is why I took the time to break this chapter into 3 parts. It doesn’t look good, as a scientific proposition, that Adam and Eve, alone, are the first couple of the whole human race. And now you know, at least dimly, the reasoning behind that. That the genetic science will be refined in the future, I have no doubt, but overturned completely; it’s not going to happen. So, from a genetics standpoint, it is Adam’s Last Stand.
However, I am going to go off on a tangent of my own (Dennis did not cover this) and speculate how Adam might be saved, in a manner of speaking. I’m going to do that by introducing the concept of Most Recent Common Ancestor (MRCA). In genetic genealogy, the most recent common ancestor (MRCA) of any set of individuals is the most recent individual from which all the people in the group are directly descended. In a 2004 article in Nature, Douglas L. T. Rohde, Steve Olson, and Joseph T. Chang presented a paper on “Modelling the recent common ancestry of all living humans”. You can read the article here. Here is the abstract of the article:
If a common ancestor of all living humans is defined as an individual who is a genealogical ancestor of all present-day people, the most recent common ancestor (MRCA) for a randomly mating population would have lived in the very recent past. However, the random mating model ignores essential aspects of population substructure, such as the tendency of individuals to choose mates from the same social group, and the relative isolation of geographically separated groups. Here we show that recent common ancestors also emerge from two models incorporating substantial population substructure. One model, designed for simplicity and theoretical insight, yields explicit mathematical results through a probabilistic analysis. A more elaborate second model, designed to capture historical population dynamics in a more realistic way, is analysed computationally through Monte Carlo simulations. These analyses suggest that the genealogies of all living humans overlap in remarkable ways in the recent past. In particular, the MRCA of all present-day humans lived just a few thousand years ago in these models. Moreover, among all individuals living more than just a few thousand years earlier than the MRCA, each present-day human has exactly the same set of genealogical ancestors.
Anyway, what they are basically saying is that, based on reasonable modelling, it is scientifically possible that a common ancestor to all of humans could have existed just several thousand years ago. Now, how reasonable is that supposition? Well, it is YALE and M— I — (FREAKING) T!!! In fact, Adam of the Bible could very well have been the ancestor of all Israel. Now, to be sure, he was not the only human alive at the time. But Genesis hints that there were other people around. Where did Cain get his wife? How did he found a city? Who was he afraid would kill him as he wandered away? It would explain the genealogies, which, according to biblical anthropologist Alice C. Linsley, were not genealogies at all but rather King’s Lists. (As an aside spend some time on Alice’s blog to get a refreshing look at the real history the bible chronicles.)
As Alice says in her article, “Are Adam and Eve Real?” :
…it is not necessary to insist that Adam and Eve are the progenitors of all humanity. Instead we may understand them as the first ancestors of the people who gave us Genesis. This concept of the first ancestors or heads of tribes and clans is found throughout the Bible. Midian is the head of the Midianites; Jacob is the head of the Israelites, and Lot is the head of the Moabites.
That makes sense to me. And it preserves the essential truth of what the Bible is trying to convey to us. But the Bible conveys this truth in the context of the views of ancient men, not in some woodenly, empirical, modernist mind set. If you can’t get shed of that modernist mind set, then you aren’t really a conservative theologian, because the only thing you are conserving is a modernist mind set, and you are setting that up as the be-all and end-all of thought. God chose to convey His truth to us through the medium of ancient writings; if you have a problem with that, then your problem is with God, not those of us trying to be faithful interpreters of what the ancients were trying to say.
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Other posts in the series: