Intelligent Design

Rapid Evolution: Is it NS or the Environment that matters?

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It a newly issued study in the PNAS, a species of lizard was transplanted 36 years ago from one island in the Adriatic to another. Tremendous phenotypic changes have occurred, the most dramatic, in my estimation, being the development of ‘cecal valves’ in the digestive tract to be able to digest the plant food that the transplanted species of lizards has taken to eating. Cecal valves occur in only 1% of all lizard populations, yet it developed in only 36 years—along with changes in head size, jaw size, and bite strength (needed to chew the cellulose found in plants)!

There seems to be two ways of looking at this: (1) that NS has brought all of these changes about; or (2) the environment, specifically the proteins/enzymes/chemicals of the plant life on the new Adriatic island has interacted with the genome to quickly bring about these changes. Considering Haldane’s Dilemna–much discussed here at UD–there have been simply too many changes that have occurred to the physiology of these lizards for NS to be invoked as the cause. Additionally, if NS “can” work this fast, then why aren’t we seeing the development of higher taxa of animals and plants right now? The old argument is that NS works too slowly to be seen, and that’s why we don’t see these higher taxa—nor the intermediate forms which would be required—in present day flora and fauna.

What we seem to be seeing isn’t exactly Lamarckism, but a kind of form of it: i.e., the environment produces changes in the phenotype of the lizards which is inheritable, but is doing so via genetic regulatory mechanisms; IOW, epigenetics.

The more we learn, the harder it is for RM+NS to keep up.

Here’s what PhysOrg.com has to say: “Observed changes in head morphology were caused by adaptation to a different food source. According to Irschick, lizards on the barren island of Pod Kopiste were well-suited to catching mobile prey, feasting mainly on insects. Life on Pod Mrcaru, where they had never lived before, offered them an abundant supply of plant foods, including the leaves and stems from native shrubs. Analysis of the stomach contents of lizards on Pod Mrcaru showed that their diet included up to two-thirds plants, depending on the season, a large increase over the population of Pod Kopiste.

“‘As a result, individuals on Pod Mrcaru have heads that are longer, wider and taller than those on Pod Kopiste, which translates into a big increase in bite force,’ says Irschick. ‘Because plants are tough and fibrous, high bite forces allow the lizards to crop smaller pieces from plants, which can help them break down the indigestible cell walls.’. . .

“Cecal valves, which were found in hatchlings, juveniles and adults on Pod Mrcaru, have never been reported for this species, including the source population on Pod Kopiste.

“’These structures actually occur in less than 1 percent of all known species of scaled reptiles,’ says Irschick. ‘Our data shows that evolution of novel structures can occur on extremely short time scales. Cecal valve evolution probably went hand-in-hand with a novel association between the lizards on Pod Mrcaru and microorganisms called nematodes that break down cellulose, which were found in their hindguts.'”

Here’s the link.

29 Replies to “Rapid Evolution: Is it NS or the Environment that matters?

  1. 1
    PaV says:

    Here’s the PNAS abstract

  2. 2
    Jon Jackson says:

    Here’s an experiment: Find the genes responsible for these new features and see if they’re present in the parent population. This should show if the features are indeed novel or if this represents an activation of dormant genes by a change in environment.

  3. 3
    nullasalus says:

    “There seems to be two ways of looking at this: (1) that NS has brought all of these changes about; or (2) the environment, specifically the proteins/enzymes/chemicals of the plant life on the new Adriatic island has interacted with the genome to quickly bring about these changes.”

    I’m curious – aren’t distinctions like this to a point somewhat arbitrary? And by that I mean, arguing that the crux of the change was natural selection (because particular traits were passed on via reproduction) versus environment (because the environment placed a particular accent on certain traits).

    In other words, it sounds like in both cases you could be describing the same process, yet pointing to different ‘driving forces’. Am I right? Wrong?

  4. 4
    JunkyardTornado says:

    If the genes were dormant they would still be present in the parent population. In any case, how would this fact be at odds with the modern evolutionary synthesis.

    As far as Lamarkism, certainly the researchers involved didn’t imply remotely anything like that. As far as I can tell differential reproductive rates based on those who had favorable characteristics to begin with was the driving force, here, correct? There was no misconception by the researchers that all those mutations happened after the lizards came to the island. They would have already been present essentially as “Junk DNA” correct? – encodings for features that were of no particular use in their previous habitat. From article:

    Examination of the lizard’s digestive tracts revealed something even more surprising. Eating more plants caused the development of new structures called cecal valves, designed to slow the passage of food by creating fermentation chambers in the gut, where microbes can break down the difficult to digest portion of plants. Cecal valves, which were found in hatchlings, juveniles and adults on Pod Mrcaru, have never been reported for this species, including the source population on Pod Kopiste.

    “These structures actually occur in less than 1 percent of all known species of scaled reptiles,” says Irschick. “Our data shows that evolution of novel structures can occur on extremely short time scales. Cecal valve evolution probably went hand-in-hand with a novel association between the lizards on Pod Mrcaru and microorganisms called nematodes that break down cellulose, which were found in their hindguts.

    So a very small percentage had an encoding for some purposeless flap in their gut to begin with, and in the new environs that trait came to characterize the entire population as a result of differential reproduction.

    Sorry for thinking out loud – I don’t see what the controversy is, or where Lamarkism in any form could be involved.

  5. 5
    JunkyardTornado says:

    I realize now that quote said the intestinal feature had never been observed before in the species – however by that I don’t think they meant it wasn’t there. On the new island if just one lizard expressed this trait then maybe he would be inherently more viable by a sizable margin than any other individual, which would directly translate into increased reproductive rate for him and his progeny on the new island. Anyway this is the simplistic filter through which I view everything.

  6. 6
    Atom says:

    PaV,

    Interesting post. I’d like to see follow-up discussion on it.

    A couple thoughts:

    1) I agree that if there were several independent structural changes that occurred to allow use of the new food type, RV+NS probably isn’t a good explanation. It takes time to stumble upon the right combination of features and the smaller the population size, the less replication resources available for trial and error.

    2) With regards to Haldane’s Dilemma, if the population of lizards was initially very small (a bottle-neck), then any change could spread fairly rapidly. But the flip side is what I mentioned above: though you can spread a trait more quickly with fewer members of a population, you are then not likely to stumble upon the right features in the first place, since you have to too few resources (population-wise) to find them.

    I’d like to hear what others think about this.

  7. 7
    JunkyardTornado says:

    Atom:

    Shouldn’t you be providing a better explanation than RV+NS, if your postulating that that wasn’t it.

    Furthermore, I don’t see how Haldane’s Dillema, which has to do with mutation rates, is even relevant here. The initial article I don’t think even mentioned mutations, did it? It seems the clear implication is that the discussed physilogical traits were already present in some very latent form in the previous population and through NS became predominant on the new island. That seems on its face, entirely plausable and noncontroversial, and before simply negating it, I think you have an obligation to provide some mechanism with equal explanatory power.

    I’m not a biologist. Maybe you are.

  8. 8
    JunkyardTornado says:

    As far as Haldane’s Dillema, I just looked at Wikipedia and I see it has to do with fixing a number of new traits simulataneously in a population (and not just mutations). But I’m thinking – say you have a stock of plant seed taken from one environment, and you take them to a radically different environment and try to grow them there, and in the first generation in that new environment, perhaps only 1/2 of 1 percent survive, and everything else dies. Guess what? What ever was still alive, its genes and whatever set of favorable traits it had in the new environment will predominant drasticially in subsequent generations, right? I’m not a farmer either, so maybe I can learn something.

  9. 9
    Atom says:

    JT,

    One doesn’t need to provide an alternative explanation to say another is not a good one. I can say “Dancing in a circle does not cause rainfall” without explaining exactly what does cause rainfall. The two are independent.

    As for Haldane’s, I’m talking about fixation of genes. The larger the population, the longer to fixation. However, small population sizes affect replication resources for accidentally stumbling on the right variation. If the all traits were already latent in the population (and we didn’t have to find them by RV), then it isn’t really an issue. (It would then be a case of front-loading.)

    If the traits existed in M individuals, then we can calculate how fast all the traits should be expected to spread given an initial population size N. If the traits spread much faster than the Haldane/ReMine limit allows, we’re probably looking at some form of environmental triggering.

  10. 10
    JunkyardTornado says:

    Does Haldane’s dillema concern primarily a stable population in a fixed environment? I can see how propogating new traits in an already optimized population would be difficult. But what about a radically new environment?

  11. 11
    JunkyardTornado says:

    OK, you mention environmental triggering. Maybe we don’t disagree about anything.

  12. 12
    Atom says:

    Also, as a nuance,

    When discussing Haldane/ReMine’s limit, we are taking into account bringing the population size back up to a fairly stable number. This is particularly relevant in ReMine’s formulation. If 6 Billion humans all have a trait, then how long would it take for one human (with the trait) to multiply into 6 Billion? Given human birth rates and gestation times, there is an objective limit as to how small that number can be.

    So your example of simple killing off every individual without a given trait does give you fixation, but you still need to bring the population size back in the area of what it was before.

    This all may or may not be directly relevant to to situation outlined in the paper, so I’m just giving background for general discussion. I’ll take an in depth look over the paper this weekend (if it is available.)

  13. 13
    PaV says:

    JT:

    I’m glad you’re thinking through Haldane’s Dilemna.

    I’m very short of time. But consider this, are there 36 generations involved? (I don’t know what the breeding time of lizards is) If so, then if, as you say, you have 1/2 of 1% surviving each year, then, at most, we would expect 36 different traits to have become ‘fixed’. Now when it comes to genes, there’s the notion of pleitropy, and so for any individual trait, more than one gene is involved, so, the total number of genes affected would have to be less than 36. CAn NS explain all of this? Again, if the answer is ‘yes’, then why haven’t we seen new species develop. When the lizard was taken to a new environment, why didn’t it become something else? This would suggest a limit to Darwinian mechanisms, or, as Behe terms it, an “edge” to evolution.

    I must run.

  14. 14
    poachy says:

    One doesn’t need to provide an alternative explanation to say another is not a good one.

    What you are describing is heckling, not science.

  15. 15
    magnan says:

    It would seem that the cecal valve change could not have developed gradually from scratch through RV + NS. There weren’t large enough populations and numbers of generations. So that leaves the chance appearance (amplified by selection) of a recessive gene already developed by RV + NS in some ancestor of the species, or some form of Lamarkian creative response to the new conditions, or a combination of the two.

    With the first explanation it would be argued that over hundreds of millions of generations the ancestors of these lizards developed and retained a repertoire of recessive rarely expressed characters maintained to rapidly respond to exactly these sort of environmental changes.

    This would be simple selection of randomly occurring normally recessive rarely expressed characters. I don’t know if the population numbers and number of generations available make this plausible. But the data mentioned in the article seems to completely debunk this explanation anyway, since the researchers state that this character has never been observed in this species.

    So this leaves Lamarkian explanations. There might be a Lamarkian causative response link between this particular environmental stress and expressing specific tailored traits already held in the genome in reserve.

    Lastly, the Lamarkian mechanism may have actually created the new character (cecal valves) from scratch in response to the environmental stress.

  16. 16
    Atom says:

    Poachy wrote:

    What you are describing is heckling, not science.

    It depends on the nature of the criticism. I am merely pointing out quantifiable difficulties with a proposed RV+NS explanation.

  17. 17
    bFast says:

    This is a very intriguing study. Let me point to the following statement in the study,

    Tail clips taken for DNA analysis confirmed that the Pod Mrcaru lizards were genetically identical to the source population on Pod Kopiste.

    This would indicate that only Natural Selection, not random mutation, is being tested here. It also shows that Natural Selection is capable of producing significant micro-evolution.

    However, the bit about the cecil valves I find highly intriguing. It is clear that the original lizzard has an unimplemented trait for cecil valve development floating around in its genes. When only 1% of scaled reptiles produce this phenomenon, one has to ask why the DNA to code for the feature didn’t degrade to mush in the original lizzard. How can unimplemented DNA (that which codes the cecil valve) maintain its integrity? I do not see how this DNA can be preserved by the only known DNA preservative — natural selection.

  18. 18
    Jorde says:

    Wouldn’t the clear alternative to RM + NS be intelligent design? Clearly there was not enough time for Darwinism to do its magic, thus the new structures were designed. Finding another ‘alternative’ is just falling into the trap of materialism.

    Jorde
    Student of the Intelligent Design Institute of Theoretical Science

  19. 19
    JunkyardTornado says:

    JT wrote: But I’m thinking – say you have a stock of plant seed taken from one environment, and you take them to a radically different environment and try to grow them there, and in the first generation in that new environment, perhaps only 1/2 of 1 percent survive, and everything else dies. Guess what? What ever was still alive, its genes and whatever set of favorable traits it had in the new environment will predominant drasticially in subsequent generations, right?

    PaV wrote: But consider this, are there 36 generations involved? (I don’t know what the breeding time of lizards is) If so, then if, as you say, you have 1/2 of 1% surviving each year, then, at most, we would expect 36 different traits to have become ‘fixed’

    No, I meant that 1/2 of 1% survived in the very first generation in the new environment. It seems quite obvious that percentage would increase from generation to generation until plateauing somewhere, not stay at 1/2 of 1 percent in perpetuity.

  20. 20
    Atom says:

    Jorde,

    Why troll?

    Intelligent Design Institute Of Theoretical Science

    Your version of BRITES?

    Not polite to go to someone’s house and call them an IDiot.

  21. 21
    PaV says:

    Atom (9):
    If the all traits were already latent in the population (and we didn’t have to find them by RV), then it isn’t really an issue. (It would then be a case of front-loading.)

    I am busy all weekend long, and will check in as best I can. But my first impression is that of Atom’s, viz., ‘front-loading’, combined with environmental triggering.

    It would seem that an easy experiment to perform in the lab—or even in a limited, constrained, outdoor environment—would be to change the food given to the original speices of lizards, and then watch for any morphological changes. This seems like the obvious follow-up study.

  22. 22
    bFast says:

    Latent — that was the word I was looking for.

    If the lizards were “genetically identical to the source population”, then the cecil valves must have been a latent trait. However, it seems that cecil valves are a rare phenomenon amongst lizards. As such, the question remains of how such a trait could persist with such a history of being latent? Latent traits should be subject to mushification due to random mutations unchecked by natural selection.

  23. 23
    EndoplasmicMessenger says:

    Reminds me of Spetner’s reference in Not By Chance (p 187-188) to Barry Hall’s work of 1982 and 1988 (Evolutionary Biology vol 15 pp 85-150 and Genetics vol 120 pp 887-897, respectively).

    In his first experiment, Hall grew bacteria that could not metabolize latose. In the presence of lactose, two point mutations were found to suddenly occur: one to a structural gene and one in its control gene. Neither of these mutations, by themselves, have any value to the bacteria. It should have taken a hundred thousand years for these two mutations to occur together. But in this very repeatable experiment, both mutations would occur in just a few days.

    His second experiment was similar but required very precise deletions and insertions. The mutations that should have taken a million years to occur happened within two weeks in 60% of the colonies.

    RM+NS certainly cannot explain this.

    Not By Chance is will worth the read. He has several solid examples along these lines.

  24. 24
    Jorde says:

    Atom, I am glad you brought that up. It is the lesson I learned from the Machine video. You can say any outrageous thing about Darwinism that you want to as long as you make some subtle point no one cares about and they will praise you for it. With something like that in your signature, you can go to PT or any place like that and insult Darwinism all you want and get praised.

    Jorde
    Student of the Intelligent Design Institute of Theoretical Science

  25. 25
    Sladjo says:

    I’m not a biology specialist, but as I can understand from the article study and it’s conclusion, this points to me to a (DNA) preloaded adaptive system, a system that is loaded with pre-programed features, maybe some sensors to detect changes in the environment and a logic that will harnest the what the sensors have detected, and put in place the right procedure that leads to new features in animal’s organs that have a role in food processing. And that’s NOT darwinian evolution…

  26. 26
    PaV says:

    Sladjo:

    I suspect you have an engineering/computer programming background, because that’s how many of us here at UD see the process working. As EM keenly points out in his post (23), Spetner, one of the most broadly educated people to have written on evolution, comes to an almost same conclusion—environmental triggers.

  27. 27
    Atom says:

    jorde wrote:

    With something like that in your signature, you can go to PT or any place like that and insult Darwinism all you want and get praised.

    But this isn’t PT. So if you enjoy posting here, you better hope DS or one of the other mods doens’t see you writing that, becuase it is grounds for banning from the blog. (See the moderation policy for details.)

    Others,

    Does anyone have any more information on the lizards, their population size after 36 years, etc? The article was fairly brief.

  28. 28
    Upright BiPed says:

    This is a very (crazily) interesting article.

    I think this thread needs a bump up after the Expelled threads taper off a bit, or perhaps some sort of follow up article if one becomes available.

  29. 29

    […] when dealing with fixation. All of this brought to mind a thread I posted just a few weeks back about the amazing phenotypic changes that had taken place in lizards transplanted from one Adriatic island to another just 36 years […]

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