Creation and Evolution (Part 18)
August 19, 2013 Time: 00:22:06
We have been talking about how to integrate our biblical understanding of creation and the world with the contemporary scientific evolutionary paradigm. You will remember last time we saw that there are three major features of the contemporary evolutionary paradigm. First is descent with modification – living organisms are descended from earlier organisms with modifications. Second would be a reconstruction of the evolutionary tree showing how all living organisms are related to each other as branches off of branches off of branches until one comes back to a single primordial ancestor. Finally, we have the explanatory mechanisms of random mutation and natural selection as the explanation for evolutionary development. What we want to look at now in more detail is the thesis of common ancestry – that all living organisms are descended from some primordial ancestor. We will leave aside for now that third point – the question of the mechanisms. Here we want to simply look at that first point – is it the case that the evidence supports the idea that all organisms share a common descent?
Common Ancestry
Here it seems to me, as I tried to look at it as objectively as I can, that the evidence seems to be mixed. The strongest evidence in favor of the thesis of common ancestry derives from the genetic similarity of virtually all living things. Almost all living organisms share the same genetic code or DNA. In fact, it is striking how similar organisms are in their DNA to one another. Moreover, the genetic similarity between organisms corresponds to their positions on the evolutionary tree of life. Organisms which are on the same branch of the tree are much more similar to each other genetically than to organisms on a different branch of the tree. For example, a bat and a whale are much more similar genetically than a bat and a lizard or a bat and a sponge.
The special creationist could respond to this by saying that God simply used the same design plan over and over again in creating biological life forms. The genetic similarity of diverse organisms doesn’t imply that one evolved from the other. To give an analogy: Ford and General Motors use the same sort of design plan to manufacture their automobiles but that doesn’t imply that a Chevrolet has evolved from a Ford. They simply have a similar design plan. Perhaps one could say that God repeatedly used the same basic design plan; namely, the same sort of genetic structure for the different unrelated organisms that he created. There was no reason to reinvent the wheel each time he created new organisms.
This is a possibility, I think. But it might seem more plausible to say that the genetic similarity of all living things is due to their being related to one another. For example, in a recent article by the population geneticist Dennis Venema of Trinity Western University[1], he specifies three genetic phenomena which are difficult for the special creationist to account for. Let me share with you these three phenomena that he pinpoints.
First, he says, the deep genetic similarity between organisms is far in excess of what is required in order for DNA to produce similar amino acids and proteins which would govern the types of organisms that are produced.[2] The genetic code permits 64 different combinations of its elements. You can combine the different elements of the genetic code into 64 different combinations. But these different combinations produce only 20 amino acids. So there is a kind of redundancy here – the same amino acid can be produced by several different combinations of the genetic code. You’ve got 64 different combinations but only 20 amino acids that result. So the same amino acid can be produced by different combinations of the elements of the code. So in order for two organisms to share similar amino acid segments, and so to be genetically similar, they don’t have to have that deep structural similarity on the level of the genetic code. And yet, time and again we find that organisms which are thought to be related share not only similar amino acid sequences but deeper similarity of genetic code combinations. This deeper unnecessary similarity would be explicable if the organisms share a common descent and hence a common genetic code. But it would seem to be unmotivated if each one were a special creation.
The second phenomenon that Venema points to is the organization of the genes of related organisms[3] suggests a common ancestry. The organization of their genes, he thinks, supports common ancestry. Two species which are thought to have recently diverged from a common ancestor have not only many of the same genes but they also have the same ordering, or sequence, of those genes. This similarity of ordering is not necessary in order for the organisms to have similar body plans and functions. They can have the same genes and hence similar body plans and functions but they don’t need to have the same ordering. And yet, they do! Special creation seems to leave this similarity unmotivated whereas common ancestry would make it intelligible. They share their ordering of their genes because they are descended from one another.
Finally, the third phenomenon is the presence of shared so-called pseudogenes in related organisms suggests common descent. A pseudogene is a defunct gene sequence that has been inactivated through mutation. It was once a functioning gene sequence but a mutation occurred which inactivated it so it is now defunct. Organisms which are thought to be closely related are found to have the same non-functioning pseudogenes even in the same order even though these defunct genes do nothing in either organism. Such similarity would make sense given common ancestry but it is hard to explain why God would reproduce in one organism the broken parts of another organism. To borrow the automotive analogy once more, it is hard to see why the designer would reproduce in one automotive model a non-functioning handle found in another model.
These arguments are far from compelling and they fall far short of demonstrating anything so sweeping as the thesis of common ancestry – that all living organisms are descended from a single primordial ancestor. Still, I think they do make special creation look rather ad hoc, or contrived, in light of the evidence. So the genetic evidence is, I think, one of the best evidences in support of the thesis of common ancestry.[4]
Discussion
Question: In Denton’s book, Evolution: A Theory in Crisis [5](he is in this field as well as a medical doctor as well as a microbiologist by training) he makes the point that as you go up and down the complexity within a family that the gene spacing stays the same even for organisms that are wildly different in morphology and gestation period and mutation rate so this speaks against this being accidental rather than a special creation because the sequencing doesn’t change.
Answer: Isn’t that the same as the second point that Venema was making that I cited? The ordering of these genes seems to suggest common ancestry.
Followup: Maybe on one hand, but on the other hand you would expect that as the gestation periods were different and the morphology was different and the mutation rates are so vastly different that you would see some movement, contraction or whatever, from the original organism. So it is the flip side in opposition to this. It is a two-edged sword because why does this not then change if these organisms are so vastly different in those areas.
Answer: OK, that is in Michael Denton’s book Evolution: A Theory in Crisis, right?
Followup: Yes. I am pulling this from my head because it has been a long time since I read it.
Answer: Yes, same here.
Question: I find the use of the genes to be no different than the discussion of morphology similarities. We’ve gone down into the genes and said “If I were the designer, I wouldn’t have done that, so therefore God would not have done that.” I think the explanations here are, “Well, look, it has some defunct thing that we really don’t know what it is doing and it is in both of those things so if God were a perfect designer he wouldn’t have done that because if I were designing it I wouldn’t have done that.” That is baloney.
Answer: I think you are making a good point. The criticism here seems to be predicated on the view that there isn’t any motivation for a designer or creator to have done that. Then that means that you are speculating about motivations and what would motivate a designer to do that. When you get into that, that does seem to be very conjectural, doesn’t it? Speculating about what possible motivations the designer could have, for example, for having the same genetic code combinations to produce these different amino acids. I think that you are making a good point.
Question: One thing that really bothers me – in Francis Collins’ book, he argues that mice and humans evolved from the same ancestry because there is this pseudogene in mice and humans that looks like it would be functioning but half way and at some point it was just cut off and it is in the junk DNA region and therefore it is evidence for common ancestry.[6] Well, I suppose if you agree with him that it literally is half a gene that was cut off (which seems to be all speculation) and is literally in the junk region that won’t eventually turn out to be functioning DNA, maybe that is evidence but I would deny that it literally is a junk region.
Answer: Yes, and Venema makes this point – don’t equate pseudogenes with junk DNA. Apparently, these aren’t exactly the same things. Granted the hope of the special creationist might be that there might be some functions found for these pseudogenes in these higher organisms.
Followup: I’m just saying that when the evidence is stated this way, there is a lot of loading the conclusion already into the presentation of the evidence. There just seems to be a lot of circularity here.[7]
Let me go onto the next point. I have suggested that the genetic evidence is probably the best evidence in favor of the thesis of common ancestry. On the other hand, the fossil evidence stands in opposition to the doctrine of common ancestry.
When Darwin proposed his theory, one of its major weaknesses was that there are no organisms today which stand midway between other organisms as the transitional forms between them. We don’t see transitional forms between the animals that are living today. They are rather like the leaves on the outer canopy of a tree and we don’t see the twigs and the branches that would lead to these leaves – we just see the leaves on the canopy. Darwin answered this objection by saying that these transitional animals all existed in the past and would eventually be discovered. However, paleontologists have unearthed a good deal of fossil remains of extinct animals since Darwin first published On the Origin of Species, and by and large they have not found these anticipated transitional forms. Instead, what they have found are just more distinct animals and plants which have died off – as it were, simply more leaves on the canopy of the tree but which are now extinct. The common branches and twigs linking them by and large have not been found.
There are, indeed, certain transitional forms like the Archaeopteryx which is a bird that exhibits certain reptilian features such as claws on his wings and teeth in his beak. But it is important to understand that when evolutionary biologists or paleontologists talk about transitional forms they are using this word in a peculiar way just as we saw the way the word “random” was used not to mean chance. Transitional form doesn’t mean “an intermediate form between some earlier form and a later form observed today.” That is not what a transitional form means. A transitional form is simply an organism that exhibits features of different types of organisms. For example, the Archaeopteryx is called a transitional form because it exhibits avian features (of birds) and reptilian features. So in that sense it is transitional. But, in fact, it is not really transitional in the sense of being an intermediate form. Here we have a PowerPoint Slide illustrating bird evolution. [see Figure 1 below.]
Figure 1 - Bird Evolution
What you will see there is that Archaeopteryx in fact doesn’t evolve into modern birds! It just goes extinct. It is not a transition from reptiles to modern birds. Modern birds originate on a quite separate branch of the tree. Moreover, the feathered dinosaurs – the troodontids – also don’t evolve into modern birds. These feathered dinosaurs were not on their way, apparently, to becoming birds. They were just reptiles that evolved feathers and they eventually went extinct. So neither Archaeopteryx nor the feathered dinosaurs are intermediate forms to modern birds. You see, you don’t really know where modern birds came from on the chart. So they are transitional simply in the sense that they exhibit features of other types of life. The Archaeopteryx has both reptilian and avian features. Similarly, the troodontids are dinosaurs (reptiles) but they have feathers. And the claim is, therefore, that they have a common ancestor which we still haven’t found. So, they are transitional in one sense but they are not transitional in the sense of being intermediates on the way to these modern life forms.
Moreover, if the thesis of common ancestry were correct, we are not talking about there being a few transitional forms like Archaeopteryx. Rather, as Michael Denton says in his book, there should be literally millions and millions of these transitional forms in the fossil record.[8] Think, for example, of all of the intermediate forms that would have to exist in order for a bat and a whale to have descended from a common ancestor. And yet, they are not there. Moreover, a bat and a whale are actually rather closely related on the evolutionary tree of life in that bats and whales are both mammals. They are both vertebrates. Think how many transitional forms would have to exist for a bat and a sponge to be descended from the same ancestor. So this problem can’t just be dismissed by saying we haven’t dug deep enough. The transitional forms haven’t been found because they don’t seem to be there. This absence would be consistent with versions of the thesis of common ancestry that appeal to leaps in the evolutionary development so you wouldn’t find the transitional forms but it would tell against versions that are gradualist in their development.
So it seems to me that the data concerning common ancestry are mixed. I think the genetic evidence does lend support to the thesis of common ancestry but the fossil evidence tends to go against it. So our final verdict will attempt to ask how we can put this evidence together in such a way as to best explain the evidence.[9]
[1] Dennis R. Venema, “Genesis and the Genome: Genomics Evidence for Human-Ape Common Ancestry and Ancestral Hominid Population Sizes”, Perspectives on Science and Christian Faith, Volume 62 Number 3, September 2010, pp. 166-78. An online copy of this article can be found at: http://www.asa3.org/ASA/PSCF/2010/PSCF9-10Venema.pdf (accessed August 20, 2013).
[2] 5:23
[3] Venema uses the term “synteny” to label this phenomenon. He says, “Synteny is a technical term for conservation of gene order along chromosomes between relatives.” (Ibid. p. 167.)
[4] 10:03
[5] Michael Denton, Evolution: A Theory in Crisis (Chevy Chase, MD: Adler & Adler, Publishers, Inc., 1986).
[6] Francis S. Collins, The Language of God: A Scientist Presents Evidence for Belief (New York: Free Press, 2006) pp. 135-37.
[7] 15:02
[8] 20:03
[9] Total Running Time: 22:05 (Copyright © 2013 William Lane Craig)