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Tuesday, September 2, 2014

Rapid Change in Lizards: An Example of Post-Flood Diversification

Posted by jlwile on May 31, 2012

An Italian wall lizard such as the ones analyzed in the study (Click for credit)

Nearly a week ago, a student sent me a web article about a study that slipped by me in 2008. According to the student, the study has been used by Richard Dawkins to show that evolution can produce entirely new structures in animals. This bothered the student, and he asked me to take a look at the web article to see what I thought of the study. Of course, the first thing I had to do was find the actual scientific paper upon which the web article was based. Once I read through the scientific paper, I thought it provided a great example of what young-earth creationists think happened after the worldwide Flood.


As I have mentioned previously, young-earth creationists are in debt to Charles Darwin, because he allows us to understand how an ark filled with two of every kind of animal (and seven each of the clean kinds) could produce all the biological diversity we see today. In case you aren’t aware, God did not command Noah to put every species of animal on the ark. Instead, He instructed Noah to take every kind of animal that needed protection from the Flood onto the ark. We young-earth creationists think that “kind” is a much broader term than “species.” For example, there are many species of cat today (tigers, lions, jaguars, domestic cats, etc.). However, we think that God created only one kind of cat.1 As a result, only two cats went on the ark, and all the cats we see today have descended from that one pair of cats.

This is why Charles Darwin is so critical to a young-earth understanding of biological history. We think that variation and natural selection are what produced all the species of cats we see today. As the one pair of cats went out from the ark, they reproduced, and their progeny spread out. As the progeny encountered new environments, they adapted to those new environments via variation and natural selection, just as Darwin envisioned.

Where we differ from modern evolutionists is that we think biological change is limited by genetics. There is a certain amount of information in a genome, and varying what kind of information is expressed in the organism will produce all sorts of diversity within a genome. However, it is not possible to add information to a genome, so it is not possible to fundamentally change a genome. Thus, while a specialized cat (like a tiger) can come from two unspecialized cats (such as those that were on the ark), there is no way that a horse can come from those cats. The genomes of horses and cats are too fundamentally different.

The study this student sent me provides a perfect example of how that works and how quickly it happens when the environment demands it!

The study focuses on a population of Italian wall lizards (Podarcis sicula) that originated from seven individuals who were taken from one island (Pod Kopiste) and transferred to another island (Pod Mrcaru) in 1971. The islands are similar, but while the lizards’ original island was rich in insect life, the new island was much richer in plant life. On their original island, the lizards primarily ate insects. As a result, their digestive system was focused on a carnivorous diet. However, since plants were significantly more abundant on their new island, as the lizard population grew, its members had to start eating more plant matter.

How were they able to switch from being primarily carnivorous to being primarily herbivorous? They developed cecal valves, which slow the passage of food through the intestines and allow microorganisms that live there to ferment plant matter so that the lizard can better digest it. The Italian wall lizards on the original island don’t have these cecal valves, but the ones on the new island do. As a result, these cecal valves are “new” structures that were produced by evolution. The web article that the student sent me quotes one of the authors as saying:

“They evolved an expanded gut to allow them to process these leaves,” Irschick said, adding it was something that had not been documented before. “This was a brand-new structure.”

However, it’s not really a brand-new structure. As the scientific article says:2

These valves are similar in overall appearance and structure to those found in herbivorous lacertid, agamid, and iguanid lizards and are not found in other populations of P. sicula or in P. melisellensis.

So in fact, the cecal values are not “brand-new” structures. They exist in other lizards. However, they are brand-new for this species, and perhaps even for the genus. Now remember, these cecal valve have appeared in these lizards since 1971, which was only 37 years before the study. The idea that these lizards could produce a completely new structure that quickly is rather hard to believe. I think a more likely explanation is that the genes necessary for the production of cecal valves were already in the genome of these lizards, but they were “turned off” because they were not needed. When the lizards were put in an environment where cecal valves were needed, the genes were “turned on” again, producing cecal valves.

This is exactly what the young-earth creationist view of adaptation would suggest. The kind of lizard from which Italian wall lizards descended had the genetic instructions for cecal valves. Because Italian wall lizards didn’t need them, however, the genes were not active in that species. They were still there, however. Thus, when the lizards needed to eat more vegetation, the genetic instructions for cecal valves were activated again, allowing rapid adaptation to the new conditions.

Now there is an easy test to see whether or not I am right about this. If we compare the full genome of the Italian wall lizards on the original island to those on the new island, the genomes should be essentially the same. However, if the cecal valves are the result of new genes (or significantly modified old genes) that were produced by mutation and natural selection, the genomes should be noticeably different. No one has done this comparison, however, as it is not easy. They did do the easy comparison, looking at mitochondrial DNA in each population of lizard. They found the two populations indistinguishable when it comes to mitochondrial DNA, but that really means nothing when it comes to answering how the cecal valves came about.

Regardless of how the cecal valves came about, we know they came about very, very quickly. This is exactly what young-earth creationism predicts. Since we think all the biological diversity we see today came from just several thousand kinds of animals that were preserved on the ark a few thousand years ago, adaptation must be rapid when new ecological conditions present themselves. Of course, that’s also what we are finding out when we study what happens to animals in such situations. As the authors of this study admit:

Recent reviews have illustrated how rapid adaptive evolution is common and may be considered the rule rather than the exception in some cases.

The more we learn about the biological sciences, the more they confirm the young-earth creationist view.

REFERENCES

1. Robinson D.A. and Cavanaugh D.P., “Evidence for a holobaraminic origin of the cats,” Creation Research Society Quarterly 35:2-14, 1988.
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2. Anthony Herrel, et al., “Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource,” Proceedings of the National Academy of Sciences 105:4792–4795, 2008.
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Comments

13 Responses to “Rapid Change in Lizards: An Example of Post-Flood Diversification”
  1. Keith says:

    A couple months ago, you wrote a fascinating article ( http://blog.drwile.com/?p=7180 ) about how octopuses could change the products of their genes without actually changing the genes themselves -and I thought that was just amazing. When you say that the genes in these Italian lizards for cecal valves were “turned on” or “turned off” as they needed them, is this another example of the mysterious “RNA editing” you mentioned in the article about the octopuses? Or is this just natural selection bringing out a trait that the lizards already had (to a smaller degree)?

  2. jlwile says:

    Keith, it’s possible that RNA editing is responsible for this, but I was thinking about something less exotic. All organisms have genes that are used for a time and then “shut off.” For example, you have genes you used when you were developing in your mother’s womb. If you used them today, it would be disastrous. Thus, your body turns them off by a process called methylation. It has been shown that methylation can be inherited, so some genes that are turned off in a parent can also remain turned off in the children.

    That’s what I am thinking here. The genes have been methylated for a long time, because the lizards didn’t need them, and that methylation was inherited. When the need arose, however, the methylation was reversed, and the genes activated again. Now that the methylation has been reversed, the offspring inherit the genes “turned on.”

  3. gracekalman says:

    Hmmm, sounds like an article L.W. might comment on. I’ll have to check back.

  4. Keith says:

    Ooh, I see. Thanks for your enlightening response Dr. Wile. I didn’t know there was such a process as methylation until now.

  5. jlwile says:

    L.W. hasn’t commented for quite some time, Grace. You are right, though – it seems like one he would comment on.

  6. jlwile says:

    Don’t worry, Keith, a lot of scientists don’t know about it, either!

  7. J.S. says:

    Dr. Wile, do you happen to know how methylation is related to what I’ve been reading lately about epigenetic changes? Are they the same thing?

  8. jlwile says:

    J.S., methylation is one mechanism by which epigenetic changes are inherited. If you inherit a gene that is turned off by methylation, then you have inherited somethg beyond what is specified by the sequence of nucleotide bases in the gene. There are other modes of epigenetic inheritance, but methylation is currently considered the most important.

  9. WSH says:

    The evolution occurring in this example would seem to fit Niles Eldridge and Stephen J. Gould’s punctuated Darwinism as well, though 30 to 40 years is still several orders of magnitude smaller than his timescales. I would strongly suspect the genome of the lizard did not gain novel nucleotide sequences, but only reshuffled bits of code or switched on an inert sequence.

  10. Jacob says:

    This is pretty amazing stuff. I am really thankful about Darwin’s book to help explain things around us and in the Bible. I’m mostly thankful for God who created such an intricate biological system that still today absolutely blows our minds, not to mention everything else!

  11. shevrae says:

    I wonder how rapid adaptive evolution will be fit into the existing evolution paradigm. It most certainly will not be used to shorten the age of the Earth. Do you think it will be used as a stopgap for instances where very old fossils match existing creatures? The explanation would be long periods of genetic stability followed by bursts of evolution. This means that just because sea turtles have not changed dramatically in 110 million years, does not mean that they won’t, given the proper environmental stimulation. As an example . . .

  12. jlwile says:

    Shevrae, as WSH pointed out, this kind of rapid adaptation will probably be considered some form of punctuated equilibrium, which is essentially what you described. This works well for evolutionists when explaining the discontinuity of the fossil record. If evolution does happen in “bursts,” then most of the transitional forms will exist for only a short time, making their fossils rare.

  13. mimivirus says:

    Thank you for these interesting blogposts!

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