Still just a lizard

| 66 Comments
Blogging on Peer-Reviewed Research
podarcis.jpg

The title gets the principal objection of any creationist out of the way: yes, this population of Podarcis sicula is still made up of lizards, but they're a different kind of lizard now. Evolution works.

Here's the story: in 1971, scientists started an experiment. They took 5 male lizards and 5 female lizards of the species Podarcis sicula from a tiny Adriatic island called Pod Kopiste, 0.09km2, and they placed them on an even tinier island, Pod Mrcaru, 0.03km2, which was also inhabited by another lizard species, Podarcis melisellensis. Then a war broke out, the Croatian War of Independence, which went on and on and meant the little islands were completely neglected for 36 years, and nature took its course. When scientists finally returned to the island and looked around, they discovered that something very interesting had happened.

Continue reading "Still just a lizard" (on Pharyngula)

66 Comments

It was humans who brought the lizards to the second island, intelligent agents. Proof that “evolution” can only occur with the help of intelligent agents, and also proof that lizards can’t turn into cows.

Sorry, had to pre-empt the usual expected IDiots nonsense.

Although cows with lizard tails and lizard heads would be hella cool.

The cecal valves are an evolutionary novelty, a brand new feature not present in the ancestral population and newly evolved in these lizards. That’s important. This is more than a simple quantitative change, but is actually an observed qualitative change in a population, the appearance of a new morphological structure.

Evolution created something new, and it did it quickly (about 30 generations), and the appearance was documented

I’m surprised enough by the speed with which this new feature (and several others) appeared, to have some doubts about its novelty. When you say it was “not present in the ancestral population”, what exactly does this mean? Are we seeing the expression of a capability that was perhaps common in some ancestral population, not selected for on the source island, but the ability to express it was not lost? Or are we seeing several actual saltations?

I can understand that the conditions for a speciation event are all present - founder effect, isolated breeding population, different ecological niche. But if we’re seeing new beneficial mutations spreading through a population, this seems extraordinary - we’re talking about a LOT of very significant beneficial mutations, occurring almost instantly (to have time to become fixed in only 30 generations).

I would speculate that we’re not seeing anything novel or not present. Instead, I propose we’re seeing gene expressions dormant in the source population but not (yet) lost, now being “turned on” as an existing switch activates an existing enhancer or enabler.

Is there any way geneticists can determine exactly what, if anything, is truly “new” here? Otherwise, it’s almost like producing a new breed of dog in 30 generations - this is just sorting, at the very margin of evolution.

Lizards are good for that. I have been into herpetology for over 10 years. One species of gecko that I own is often wild caught. There is an extreme variety in these geckos. However it seems very little is done to track the populations. Chances are good a few of these are new species and subspecies. The problem is few know were these are collected and few do anything to research these animals. These geckos are no mystery either. I am talking about the Tokay gecko. This species has an impressive coverage of many different habitats. It has also been introduced into many areas around the world. Although people seem focused on its feet I am willing to be it has other surprises for us.

Small lizards may hold a great deal of insights into evolution. From my experience there isn’t much research into small lizards and reptiles. Most of what I do find is from people like me who collect and breed the animals. Then go on to write about them. Personally I think this is a great chance. I would love to study lizards. However the problem of money for school kinda puts that on hold.

Lizards are very well studied in evolutionary biology. Much of what we know about competition for example comes from lizard studies (e.g. Anolis lizards studies by Roughgarden, Losos, ect.)

It just proves that the pre-flood lizard was a vegitarian.

PZ Meyers:

Evolution works.

This experiment doesn’t prove that evolution works. It proves that species can quickly change their morphology. The question remains: How?

Flint:

I would speculate that we’re not seeing anything novel or not present. Instead, I propose we’re seeing gene expressions dormant in the source population but not (yet) lost, now being “turned on” as an existing switch activates an existing enhancer or enabler.

I agree. This can easily be explained through a combination of “front-loading” and environmental triggering: ID has been talking about this for years.

Long ago creationists (a.k.a. ID’ers) anticipated this kind of stuff so they undertook their own experiment. They tested their mettle by trying to cross an abalone with a crocodile. What they had hoped to demonstrate to the scientific community that such a match would refute evolution. They were looking for an “aba-dile” but like all of their pseudo-experiments all they ended up with was a “croco-balone.” Even today they keep repeating this experiment but always with the same results.

DavidK: You’re comical, but not topical. All these changes in 30 years–OR LESS–is an embarassment of riches for Darwinism. It shows “macroevolution” at work, not “microevolution”; which, in case you’re not aware of it, Darwin rejected as a mechanism (despite T. Huxley’s urgings of the contrary) for his theory.

Sorry, I couldn’t resist the opportunity. Then again, there are many off-topic comments on the line. On the other hand, give the lizard a little bit more time than 30 years (100, 1000, 10000 years or more) when BlastfromthePast won’t be around and let’s see what transpires.

Blast:

I agree. This can easily be explained through a combination of “front-loading” and environmental triggering: ID has been talking about this for years.

But what the ID folks are referring to with this terminology is not the situation I described. Maybe I wasn’t clear: I’m not saying these capabilities were somehow magically packaged in “at creation”, which is what I understand the ID folks to be saying. Instead, I’m saying that these morphological features already evolved in the fairly recent past (within the past 15 million years, perhaps), probably taking a million years to do so.

In a more scientific and less religious sense, I see nearly every if not every genome cram-packed with latent or dormant capabilities layered on like the growth of a pearl over evolutionary time and what’s passed down through common ancestry. As branching events take place, I think we see a combination of latent capabilities combining with brand shiny new mutations, to create new features and capabilities, which truly ARE novel. And these in turn are recorded in the genome, possibly to end up conferring some sort of unanticipatable benefit in the future, possibly to degrade away to uselessness.

Somehow, I missed the ID “theorists” proposing that nearly every “new” genetic or morphological feature is a combination of existing capabilities and new mutations, making evolution partly driven by historical source material and partially driven by novel sources of new variation (through everything from sexual mixing to imperfect replication to cosmic rays).

Instead, I read the “front-loading” IDiots as arguing that ALL genomes have ALL the variation in them necessary for ALL possible speciation forever, nothing new ever added, and this situation hasn’t changed since some invisible supernatural magician POOFED everything into existence. But of course, no biologist is going to claim that a new species invents a whole new genome at the one extreme, or that nothing new is ever introduced to the genome at the other. In the case of these lizards, I’m speculating that little if anything new has had time to contribute changes of this magnitude. But maybe I’m wrong.

ID has been talking about this for years.

Talk talk talk. What experiments have they done?

This experiment doesn’t prove that evolution works. It proves that species can quickly change their morphology.

Um, if species are shown to “quickly change their morphology”, apparently from pressures exerted by a changing environment, apparently through the mechanism of natural selection (to a new food source and lifestyle), um, how is that not “evolution working”?

The truth always wins out. You can tell by how those IDists who are anti-truth eventually have to argue.

“2+2 doesn’t equal 4!” they exclaim. “Rather, when two apples are combined with two other apples, they happen to then exist as four apples. But this is hardly proof of 2+2 = 4.”

In time, a genetic analysis can be done. Whether it’s really worth the time and money is another question. It is my understanding that adaptations can take place very quickly, utilizing variation that is already present in the population. Longer term evolutionary activity requires a signficant “turnover” of the genome. Personally, I suspect that certain types of genetic events (eg., gene duplication) have more implications for long term evolution.

stevaroni wrote:

Um, if species are shown to “quickly change their morphology”, apparently from pressures exerted by a changing environment, apparently through the mechanism of natural selection (to a new food source and lifestyle), um, how is that not “evolution working”?

Because BFTP says so.

Duh.

Perhaps someone more well versed in taxonomy and systematics then I has immediate examples, but I’d say most often if you have a demonstrably different diet, distinguishable morphology, and different geography you would give this animal a new species name if you just found the two of these on seperate islands and had no idea about their history.

In terms of the mechanics the new muscle in the digestive tract probably is present in very low frequencies in the ancestral population. That is not particularly relevant to whether or not there was evolution happening and forming a new species. If the original mutation occured 10 years ago, 50 years ago, or has been preserved as a neutral mutation for 100,000 years in the population doesn’t really matter. It was available variation that in a different context produced a fitness advantage.

BlastfromthePast should also be aware that Darwin’s particular preference for the pace of evolutionary change is not terribly relevant. This rapid change during a speciation event is exactly what punctuated equilibrium predicts. It also fits with patterns seen in lab selection experiments where what are superficially different conditions actually change a wide variety of selection parameters and can lead to a great deal of change in relatively few generations.

My initial reaction is identical with Flint. (But not with BlastfromthePast. I fail to see why it would be “front-loading” if the ancestors of the family had a diet similar to what is available on Pod Mrcaru.) 30 generations is extremely fast even for a single allele to become fixed (although in this case the founder effect should greatly help, I think). A saltation is out of the question, even by tradition. And a gradual sequence of several mutations just doesn’t sound feasible at all given the short time interval.

So instead of the evolution of a novelty, my hypothesis is that a single regulatory mutation, turning the structure back on in the phenotype, was already present in one of the ten individuals brought to Pod Kopiste, and was brought to quick fixation by the founder effect and the diet available on Pod Mrcaru.

I’d like to know if the lizard has a mutated enzyme like hoatzins or langur monkeys to help digest the bacteria from the fermentation.

You are all missing the point!!! This was foretold in the Old Testament.

These lizards were clearly frontloaded for cecal valves in the Garden of Eden, 6,000 years ago. The Designer knew they would be kidnapped in 1971 by evil Darwinists and transplanted.

They are also clearly god’s the Designer’s chosen lizards. They managed to exterminate the resident Canaanites native species in a minor genocidal war. And they don’t eat shellfish or wear clothes made from two different fibers.

Like Ham says, you need to look at the data through the lens of the bible to really understand what is going on.

stevaroni: Um, if species are shown to “quickly change their morphology”, apparently from pressures exerted by a changing environment, apparently through the mechanism of natural selection (to a new food source and lifestyle), um, how is that not “evolution working”?

… “It’s not pollution that’s harming the Earth. It’s the impurities in the air and water.”

Just wondering what the possible outcome would be if they were left there for 3,600 years? Do these gradual adaptations produce new species?

Just wondering what the possible outcome would be if they were left there for 3,600 years? Do these gradual adaptations produce new species?

You bet! In 3600 years, they’d evolve into mockingbirds and fly straight back home!

It has been known for a while that species can change drastically in a short period of time.

Dogs descended from wolves within 10,000 years. Does a spaniel or chihuahua look like a wolf? [These differences have little to do with modern breeding which seeks to prevent morphological change and has resulted in breeds with very little genetic variation.]

Or corn from teosinte, within the last 5K years. The changes from teosinte to corn are known somewhat. It apparently took changes in a few alleles and no major mutations to produce the crop form.

Most species have a lot of variation, much of it cryptic. IMO, the rate limiting step in evolution is selection pressure, not mutation frequency.

IMO, the rate limiting step in evolution is selection pressure, not mutation frequency.

I don’t understand. Even if we grant that there’s a lot of variation and existing potential, even if we agree that the capability for massive morphological change without further mutation is already there, still it would seem that there HAS to be a limit before existing variation runs out of gas and one must simply wait for the happenstance of fortuituous mutation. If this were not so, Behe’s front-loading would indeed be accurate.

Gould wrote at some length about the “glass sphere”, a sort of existing limit of potential variation of any given genome. Species can be artificially bred in any “direction” to the point where they hit the surface of that sphere, and there they stop. To move the sphere itself, as a whole, requires mutation.

And so we can breed chihuahuas and great danes and greyhounds, but we quickly hit a limit beyond which mutation is required to continue. Corn left to its own devices quickly returns to teosinte; the world’s entire corn crop is maintained through constant artificial assistance. Feral dogs of all specialized breeds quickly interbreed into mutts which soon look a lot like, and can probably breed with, wolves and coyotes. The loss of the ability to interbreed, it seems to me, requires mutation, not just reshuffling of the existing deck.

And so it would seem that it’s mutation, not selection pressure, which is the true throttle on evolution. Perhaps this is what creationists are kind of driving at with their micro and macro evolution blather - the distinction between adaptability inherent in the existing genome, and evolution at higher taxonomic levels resulting from beneficial mutations. To draw an automotive analogy, existing genetic variation gives you great acceleration, but only mutation can give you sustained top end. You can move rapidly to the surface of the glass sphere, which isn’t all that far away. But the grand sweep of life arises from moving (more accurately, budding) spheres. Mutation.

These result show clearly that the lizard God intervened to bestow them the much-needed stomach muscles to digest plants.

This debunks both Evolution and Christianity. So there.

[quote]Most species have a lot of variation, much of it cryptic. IMO, the rate limiting step in evolution is selection pressure, not mutation frequency.[/quote]

Don’t you think that kinda depends on population size? We’re talking about an initial population of 10 here, having a habitat of 0.03 km2 to expand into. The islet might be a scenic paradise, but not exactly a paradise for genetic variation.

In regards to the variation and mutation issue, I think the most accurate way to view it is to think of the rate of evolution is capable of initially a very rapid burst of change with a new set of selection pressures (which can be seen in this case or numerous lab selection experiments) and then you approach the limit asymptotically. The only thing is that mutation is continuously moving the asymptote out a little bit at a time.

The basic definition of evolution is change in the genetic make up of a population. Based on the few sequences which have been studied, it seems the new population is no different than its parent population. Whether we are seeing morphological and behavioral plasticity present, but unexpressed, in the parent population; or if there are correlated genetic differences in the new population has not been addressed so far as I can tell. I speculate that there have been correlated genetic changes; but speculation is all I can manage based on what I know.

Jim Thomerson:

Based on the few sequences which have been studied, it seems the new population is no different than its parent population. Whether we are seeing morphological and behavioral plasticity present, but unexpressed, in the parent population; or if there are correlated genetic differences in the new population has not been addressed so far as I can tell. I speculate that there have been correlated genetic changes; but speculation is all I can manage based on what I know.

The only DNA sequences mentioned in the paper (actually in the supplementary information) were mitochondrial ribosomal sequences used for identifying the species. That information tells us nothing about the genetic distance between this new population and the parental population. Many seem concerned about the apparent speed of this divergence, but faster genetic divergence and isolation has been reported in sympatric populations: Hendry and colleagues found one founding population of salmon diverged into two morphologically and genetically distinct populations over 13 generations (Science 290:516-518, 2000). I think it is quite reasonable to get the reported phenotypic changes in 30 generations of allopatry.

Vaughn

God did it. No other explanation is needed.

You’d think that the IDiots would be pouring all over this island looking for finger prints. The hand of God passing within the last 30 years has to be closer to God than they have ever been.

I’m becoming more convinced this is a semantic issue. If evolution describes the change in allele distribution within a population, then clearly a great deal of evolution can happen within the glass sphere, without anything novel ever being introduced. So let’s say BPH’s experiment is performed: Take half a dozen lizard pairs, move them to a new environment, and observe the changes over a couple decades. Then grab half a dozen pairs from this changed popultion and put them back. Let’s say they revert right back to where they were (even without interbreeding with the lizards left behind).

OK, now did our test lizards “evolve” twice? Once? No “real” evolution?

(Incidentally, Gould did not create the glass sphere metaphor. His discussion of it happened to be the one I noticed.)

How, EXACTLY, did you ‘determine’ that any novel information was actually required, given that even small populations have variations?

This question, slightly redirected, is something I’d like to see answered. How WOULD any qualified scientist determine if anything “novel” occurred? The changes we observe MIGHT be the result of some (IMO incredibly fortuituous and unlikely) new mutations, or it MIGHT be inherent in the source lizards, rarely expressed in the old environment because it wasn’t helpful, but what was selected in the new environment was the *existing* capability to express *existing* phenotypic changes. And in that case, are we seeing “amazingly rapid evolution”, or would it make more sense to say we are seeing the entirely ordinary influence of a breeding program?

My reading is, IF this is a matter of gene expression, determining this is beyond the current state of the art. We simply don’t know how to indentify an enhancer strand of DNA somewhere in the genome, or how to identify capabilites of a gene that are not currently being expressed because that enhancer isn’t being deployed.

This would be analogous to examining all the data coursing through every communication system in the world, and examining everyone looking at any of those data, and predicting how THIS person might respond to any of it. Just by examining the person. I wonder if this is even possible.

But possibly, after the fact, we could go back to the source lizard population and notice that, yea verily, they DO have such a DNA strand outside the genes, and the target genes DO have the same receptors - but in their case, the two aren’t hooking up. And NOW, we have a better idea what happens when they hook up.

Actually, this type of thing is probably quite common. Changes in allele frequency bring about adaptation to new environmental conditions without requiring any new genetic information. Then, when conditions change again, the population once again adapts, perhaps by reverting to allele frequencies closer to the original. In this case, by definition, evolution has occurred twice, or perhaps it would be more corrrect to say that evolution is occurring continuously.

This situation is much more clear in simple phenotypic polymorpohisms where the genetic basis is more clearly understood. The peppered moths of England come to mind as one example.

However, this doesn’t mean that recombination, mutation, regulatory changes, gene duplication, etc. are not important over longer time scales. It only means that there is always genetic variation in the population and that poulations will always change over time if the environment changes, or go extinct.

Flint may be right. It might be extremely difficult to determine the exact genetic events responsible for this particular change. It might not be worth the effort inviolved, or it might be. If the genes that control this character are already known, then a comparative sequencing effort might yield the answer fairly easily. If, on the other hand, the genes are not known, or if unknown regulatory mechanisms are invovled, it might take considerably more effort to determine the exact nature of the changes involved. If the genetic changes are determined, I’m sure that PBH will be more than happy to tell us where the “information” came from.

Of course, either way, scientists will be looking for natural explanations and known genetic mechanisms, God would not enter into the equation. Ron is correct, if the ID crowd think that God was involved, (or the mysterious lizard designer in the sky), this is the perfect chance to dust for fingerprints. Shouldn’t they be the ones doing the sequencing? Now why would God care what happened to a bunch of lizards anyway?

Shebardigan said:

Ah. That would answer the question “Where on the Ark did Noah keep all of the species of termites, carpenter ants and other wood-loving critters?”

Duh! He just kept them in the ark. That’s easily enough material to feed generations of termites till the forests can regenerate. Why do you think the ark has never been found?

Honestly. It’s so obvious.

prof wierd:

Experiments with the hsp90 gene of Drosophila (fruit flies) and Arabidopsis (plant) show that polygenic traits can become fixed in FOUR generations … After selecting for the new traits for four generations, screening showed that their hsp90 levels were normal - the new phenotype was now ‘locked in’.

How do you know that the gene became fixed? All you really know is that normal levels of the protein were observed after four generations.

You ‘determined’ that HOW, exactly, given that no DNA polymerase is perfect ?

I should have written one single mutation in a particular location of the genome.

your ‘alternative explanation’ is what ?

The ingested/digested proteins and chemicals from the plant life on the island affected the genome’s regulatory mechanisms in an epigenetic fashion.

and being ‘highly correlated with other genes’ is not really a problem if expression of a regulatory gene is altered.

I agree; and this certainly remains a plausible alternative.

Just fascinating. As a layman interested in various aspects of biology, zoology and so forth, I grew up with the idea that evolution was a relatively slow process, not readily observed in the human time scale. Not only that, but that evolution moved at a rate uniform to all living things.

This was a child’s idea, of course. As I’ve gotten older and a bit more informed, I find the truth to be far more interesting. This study on lizards is a great example of the dynamic motion of evolution. Many thanks for the post and the informed comments.

About this Entry

This page contains a single entry by PZ Myers published on April 23, 2008 10:02 AM.

Richard Dawkins: The cost of “Expelled” was the previous entry in this blog.

Yoko Ono sues “Expelled” filmmakers over Imagine is the next entry in this blog.

Find recent content on the main index or look in the archives to find all content.

Categories

Archives

Author Archives

Powered by Movable Type 4.381

Site Meter