[00:00:04] Speaker A: Id the Future, a podcast about evolution and intelligent design.
[00:00:12] Speaker B: Welcome to id the future. I'm Andrew McDermott. Well, today I'm delighted to welcome back to the program Dr. Gunter Beckley. Dr. Beckley is a german paleo entomologist who specializes in the fossil history and systematics of insects, the most diverse group of animals. He served as curator for amber and fossil insects in the department of paleontology at the State Museum of Natural History in Stutgart, Germany. He is also a senior fellow with Discovery Institute's center for Science and Culture. Dr. Beckley earned his phd in geosciences from Eberhardt Carls University in Tubingen, Germany. Gunther, welcome back to id the future.
[00:00:53] Speaker A: Hi Andrew. Nice to chat again with you.
[00:00:56] Speaker B: Well, you've been publishing a fascinating weekly article
[email protected] since the summer of 2022, called Fossil Friday. Each week you illuminate the story of a different fossil, explaining the part it plays in the larger story of the fossil record while questioning the evolutionary assumptions related to it. Each piece is accompanied by at least one striking image of the fossil being discussed. Sometimes it's an image you've taken yourself from your own collection. It's a great series, to be sure. One installment I specifically enjoyed lately and thought we could unpack a little on the podcast is about caterpillars and the amazing process of metamorphosis. Now this miraculous development was featured in a beautiful 2011 documentary film from illustrator called metamorphosis listeners. If you haven't watched it yet, you're in for a treat. Discovery Institute Press also published a companion book about metamorphosis, and it was called that, edited by David Klinghoffer, complete with some stunning full color photos and an introduction from novelist Dean Koontz.
Gunter, let's start with the phenomenon of metamorphosis, first discovered by british physician William Harvey and dutch biologist Jan Swamerdam. Remind us what this process is and why it's a conundrum for evolutionary biologists.
[00:02:17] Speaker A: Sure. So it's quite interesting that you mention Harvey and swamidas, because the modern debate about the origin of metamorphosis was, in a way, foreshadowed already by a controversy between these two early biologists. So Harvey, in 1651, suggested that the poople stage in insect metamorphosis is a kind of second egg, and that was ridiculed by his colleague Swamadam, who was very unkind and said, this is complete nonsense. And Harvey's work contains as many errors as work, and Swamadav instead thought of the pooper as a kind of oviform nymph, as he called it. And so Harvey thought more in terms of a discontinuous development with the poopa, repeating embryonic processes, while swamadam thought of a continuous series of larval stages. That exactly is what is still debated today, almost 400 years later.
So let's have a brief recapitulation to understand what the problem is and what this process is. And we first have to understand that insects are different from vertebrates. So vertebrates are hard on the inside and soft on the outside. And insects, like all arthropods, have an exoskeleton. They are hard on the outside and soft on the inside. And that means they have to grow by molting. The development by molding is then controlled by two hormones. And these two hormones, the first one is ectisone. It's called ectisone. And this hormone stimulates the molting. So when it is produced, then a new molting is occurring from one larval stage into the next. And there is another hormone that is called juvenile hormone and that controls the differentiation. So if you have a high level of this juvenile hormone, then the change into the adult is suppressed. And each molding of the lava is more or less similar to the previous lava. And the lower the level of the juvenile hormone gets, the more similar the next mold of the larvae gets to the adult. Or when the level is lower than a certain threshold, then in holometabolans, the poopa is produced, which then the final adult stage is emerging from. So these two hormones control the whole development. In both major groups of insects, those with and those without metamorphosis, those without are called hemimetabolus. And these include more primitive insects like cockroaches and locusts and cicadas and bugs. And there each nymphal instar is getting more similar to the adult and is just growing in size with each molding. And the wing sheets are getting bigger and bigger. But it's a gradual development.
But most species of insects, and actually most species of animal at all, belong to the group called holometabola, which have this complete metamorphosis with a poople stage. And these insects, for example, include neuroptrans, that would be lace wings, and beetles and bees and wasps and flies and fleas and moths and butterflies and so on. And they have an enormous diversity in terms of species. There have been more than 1 million species described. And for this reason, there were two publications in 2014 by Nicholson et al and Rainfort Etal, who said that this metamorphosis obviously was the key innovation that has driven the diversification of insects. So what is characteristical in this metamorphosis is that the larvae has a very different body plan from the adult insect. And after the final larval stage, after the final caterpillar like stage, you get this resting stage, which is called pupa or crusolis. And there the body is totally rearranged. It dissolves into a kind of soup. And then from the different larval body, the, again, totally different adult body is formed. And the precursors of the wings, the wing sheets, are so called invaginated. So the larvae, or the poopa, has no external larval wings. And for this reason, the holometabolans have also been called endoptericota. So the internal wings, this would be translated to. So the difference between these two modes of larval development is so stark and so discontinuous that, of course, you have to ask yourself, how can one evolve from the other with small changes, in a darwinian way, where every change produces a viable and even advantageous change without disrupting this very sensitive developmental process? And in terms of advantage, why do you have this kind of metamorphosis at all? Scientists suggested two possibilities. One is that the lava and adult are defect to different organisms with different food and different habitats, so they do not compete with each other for the same resources. And the other suggestion was that you have a kind of decoupling of the growth process from the differentiation of the lava into the adult. That would mean that the sensitive stage, where the insect is vulnerable due to this body transformation is very short. And the longest period of the larval development is just growing in size. So that is basically the background of the insect development.
[00:08:20] Speaker B: Okay. Yeah, it's a fascinating process, and it sounds like it's a very old debate. Then 400 years they've been trying to think about this.
So today, though, you mentioned that there are only three hypotheses for the evolution of metamorphosis. Can you briefly touch on each one?
[00:08:37] Speaker A: Yeah, sure. So, of course, in my article, when I said it's three hypotheses, that's a little bit of simplification. In reality, there were some more hypotheses suggested, but most of them are fringe. So one fringe hypothesis is this, Donald Williamson's hypothesis from 2009, who suggested that two different phyla of arthropods hybridized where an insect egg was fertilized by a velvet worm sperm, which is generally considered as rubbish and was also refuted by dna sequencing. There is no dna of velvet worms in insects. But interestingly, the same scientist also suggested that this kind of freak event might be responsible for the cambrian explosion, but it's not taken seriously in the mainstream. Another fringe idea was suggested in 1914 by Poyakov, and later by Hinton, who suggested that the adult stage was subdivided into poopa and the real adult, the Margo. And so that there was the poople stage, in a way, intercolated into the development process. But this was also not getting much support. So basically, there are two main competing hypothesis left. One you could call the Hinton hypothesis, because it was suggested by british entomologist Howard Hinton in 1963. And he said that the holometabolan larval stages, so the caterpillar larval stages are equivalent to the nymphal stages of, let's say, cockroaches or other hemimetabolan insects, and that the poopal stage of holometabola is equivalent to the final nymphal instar of a cockroach or locust. And Hinton's hypothesis was initially very much supported by other scientists based on different lines of data, so from the fossil record and from phylogeny and from hormone research, but later fell out of favor because an older idea got traction then. And this older idea was initially suggested by an italian entomologist called Antonio Belize in 1913 already. And he called his hypothesis the de embryonization hypothesis, based on an original idea by Harvey from 1651. And like Harvey, Berlaser suggested that the larval stage of hemimetabolans and of holometabolans. So cockroach larvae and caterpillar larvae are not equivalent, are not homologous, but that the caterpillar larvae are equivalent to embryonic stages in the egg of other insects, and that all the other larval or nymphal instars, let's say, of cockroaches or locusts, are in holometabolans, collapsed or condensed into this kind of single poople stage.
But this idea was then further developed in the 20th century by Truman and Riddiford, especially in 1999. There was a seminal paper by these two authors and later further expanded in the. They called it the pro nymph hypothesis. Their main modification of this original hypothesis by Berlais is that they said what produced the caterpillar lava is the final embryonic stage in hemimetabolans, which is a kind of hatching stage that immediately after hatching from the egg, molds into the first nymphal insta, and that this is equivalent to all the caterpillar stages. And then all the nymphal stages are condensed into this poople stage. And this is very much now the consensus view. There's, of course, a paper by Mondal in 2019, and he said it's the most positively accepted hypothesis among the entomologists today.
[00:12:52] Speaker B: Okay, the pro nymph hypothesis. All right. Well, you relate two formidable challenges to that current hypothesis in your work. Can you share that with us?
[00:13:03] Speaker A: Yes. So the main problems with this hypothesis is that the pro nymph in hemimeter bolans is not a feeding stage. As I said, the final embryonic stage, it does not have functional mouth parts it cannot eat. And the caterpillar lava, to which it should be equivalent, is a pure feeding stage. It has been called as a kind of gut with legs. So it's the total opposite. So the question is, how could a non feeding stage develop into a basically only feeding state, which does nothing else, when one state doesn't even have functional mouthpieces? And the second problem is the question, how can you get this kind of resting stage, the poopa, where the whole body plan is dissolved without disrupting the developmental process? Because you have to imagine even the brain is dissolved and is rearranged, so that this is not something where you can easily imagine functional intermediate stages.
And it's not just that this appears unlikely, but it's inconceivable or virtually impossible, because if you think about it, if the pro nymph hypothesis is correct and the caterpillar is a kind of embryonic stage, then you require a poople stage from the very beginning, because you do not longer have this kind of gradual molting of a nymph more and more into adult like stages. Immediately when you have the caterpillar, which is an embryonic stage, you require the pupil stage to have the transformation into the adult, and then you get a kind of chicken egg problem.
So these are the two main problems. The first problem, I quoted a paper from 2012 in my article from Scientific American, which shows how clueless scientists are in terms of addressing this problem. And their jabbar in 2012 said, perhaps 280,000,000 years ago, through a chance mutations, some pro nyms failed to absorb all the yolk in their eggs, leaving a precious resource unused. And in response to this unfavorable situation, some pro nyms gained a new talent, the ability to actively feed so miraculously whoops. When they needed the new trade appeared. But this is, of course, a non explanation. And the situation is even worse for the second problem. For the origin of the poopa. And incidentally, there was also in 2019, a new study by Gindra. And what this author did is he looked at the timing of the expression of the genes that either repress or promote these developmental hormones. And he found strong support for Hindus hypothesis. So not for the pronim hypothesis, but for the alternative hypothesis, which suggests that the larvae of hemimetabolans and holometabolans are equivalent because they have exactly the same timing pattern for these gene activations and for the hormones. So this would strongly contradict the modern consensus of the pro nymph hypothesis. And this shows what we already have alluded to, that this 400 year old conflict between Harvey and swamadam is very much alive, and science did not make much progress in solving this problem.
[00:16:36] Speaker B: Interesting. So what we get from biologists are basically vague speculations and an appeal to millions of years of gradual change. But the fossil record doesn't support such a story. Does it tell us how the butterfly fits into the fossil record and why? It's a good illustration of the waiting times problem.
[00:16:54] Speaker A: Yeah. So butterflies is more of a special problem because, especially for the origin of the larval prolax, where we will later talk about more, because butterflies are very much subordinate groups within holometabolin insects. And while moths first appeared in the permotriac, true dernal butterflies only appeared with modern families already in the lower tertiary, which is now called paleogene period. But what you alluded to, this waiting time problem for metamorphosis and its origin in general, is the very early appearance of crown group holometabolin insects in general. So insects like wasps and beetles and scorpion flies, which appear in the fossil record of the upper Carboniferous, which is also called pennsylvanian, not much later than the very first fossils of winged insects. And that is, of course strange. But when you look at molecular data, the problem gets even bigger, because molecular clock data suggests that holometabola are at least as old as the earliest fossil record of flying insects. And some even suggest that they already originated in the lower carboniferous, so would be much older than estimations by the fossil record and by phylogenetic reconstructions. And there has been, again in 2019, there are a lot of papers in 2019, because there was a special volume of the journal PNA of the Royal Society on the origin of insect Metamorphosis. And there was a study by Montana etal, and they looked on the most modern data from molecular clock and up to date fossil record, and they estimated that holometabolans even originated in the Devonian 389,000,000 years ago. And this means there simply was no time for this complex physiology of metamorphosis to evolve from hemimetabolus winged insects. And this is presenting yet another example of this waiting time problem.
[00:19:08] Speaker B: Yeah. Well, in your article, you discuss the origin of pro legs, the pairs of abdominal leglets, caterpillars and their, well, caterpillar larvae possess, in addition to the standard thoracic legs. What are some of the explanations put forward to explain where those leglets came from? The pro legs.
[00:19:27] Speaker A: Yeah. So these leg legs are interesting because, as you said, usually adult winged insects and their limbs only have these three pairs of thoracic legs. That's why insects are also called hexapodes, the six footed animals. But the caterpillar larvae of butterflies or plant wasps has these additional chubby abdominal leglets, which are called prolags. And these pose, as it was called in a paper last year by Palladi in 2023, an evolutionary mystery where scientists have long grappled over. And three hypotheses have been suggested to explain this. One is that prolags are serially homologous. So equivalent thoracic legs to the legs at the breast segment of insects. So this would mean that they would have developed from something like the abdominal legs of crustaceans, because crustaceans are believed to be close relatives of insects in modern phylogeny. But this alternative was challenged and refuted by Iwo devo studies.
Another suggestion was that prolax are totally novel structures, novel adaptations that originated de novo without any immediate precursor structures. And the third alternative is that prolax are derived from so called endites. And endites are, again, if you compare it with crustacean limbs, are structures at the base of the crustacean limbs that are facing inside.
And these are believed to be possible homologues to these abdominal leg lights. But the problem is that none of the winged insects do possess such end eyes on the abdomen. So you lack the precursor structures. So how could they develop from them?
[00:21:30] Speaker B: Well, and you evaluate the claims of a new study published in the fall of 2023 by Matsuoka Edal that suggests that these caterpillar prolegs are novel traits, but based on the reactivation of preexisting endite genes, which is basically a throwback to the supposed primitive crustacean cousins of insects. Can you explain what the paper is claiming there?
[00:21:54] Speaker A: Yeah. So they looked at these three hypotheses and tried to test them with ibodevo data and proposed a kind of hybrid hypothesis of the latter two alternatives.
So what they didn't find, or what they could not find, were genetic markers for thoracic legs. This would refute, again, this thoracic leg hypothesis, but they did find genetic markers for gene regulatory networks that control endides that would confirm this homology with endites. And based on this result, and based on rna sequencing of the prolac transcriptome, so they found sequence similarity of the genes that code the prolac with the genes that produce endides. And based on the character distribution of prolags, the authors suggested that caterpillar prolagues are novel traits, as proposed by one of the alternatives, but are still homologous to endites because they were, in a way, reactivated, preexisting but dormant endite genes that then got reactivated and expressed, even though they were kind of sleeping for millions of years. And the press release in this paper made it quite clear, it said prolaks seemed to be modified endites. As crustaceans evolved into insects, endites were largely lost. But in butterflies and moths, the gene for them got reactivated, providing caterpillars with their prolags. So that's what they suggested as solution to this problem.
[00:23:39] Speaker B: Okay. And there's a few problems with this. One of them I learned Dolo's law. It's a violation of that. Can you explain a couple of the problems with this new paper's proposal?
[00:23:52] Speaker A: Yeah. Again, there are two major problems. So one is a temporal problem. It's the problem of the time span for which these genes for expression of the prolax were deactivated, because this deactivation time of the genes was so long. And you can estimate this based on the character distribution and the phylogenetic trees and the molecular datings and so on, of the branching events, that a reactivation would have been simply impossible, even based on mainstream estimates of the constraint temporal constraints, how long is such a reactivation possible? And so this would imply a violation of this famous law of evolution, which is called dollar's law of irreversibility, so that evolution does not repeat itself, because it's a kind of complex, contingent historical narrative that cannot be rewound and repeated in the same way. And the second problem is that, of course, this event, because the reactivation would happen after such a long time of deactivation of the gene, would be an extremely unlikely event. But still, it would have to have happened numerous times independently, because Prolax have such an incongruent distribution among the different groups of holometabolin insects that mainstream experts do not propose that they belong to the makeup of the common ancestor of all holometabolans, but that they originated multiple times convergently. So this unlikely event would have to happen many times independently, which, of course, makes this whole story quite absurd. So these are the two major problems that I see with this hypothesis.
[00:25:53] Speaker B: Yeah, and I was intrigued about the dolo's law, because I hadn't heard about that before. And from an evolutionary standpoint, the question remains, can functions that have laid dormant for huge swaths of geologic time suddenly get turned on again? I can see that within a design perspective, things that were built in and ready to be turned on. But when you're trying to explain life from an evolutionary standpoint, that can be difficult. I even saw the phrase stochastic silencing, which sounds a bit ominous, especially if you're an organism trying to turn functions on after a long time. Does this describe the limitations of such reactivation?
[00:26:37] Speaker A: Yes. So that, of course, is just a fancy term. So stochastic silencing sounds ominous. But it's quite simple fact that if you have a dormant gene that is no longer under control of natural selection because it is not expressed and therefore is not selected for, if there are disadvantages, then random mutations would quickly accumulate genetic noise and would disrupt the functional information of the gene. So that is called stochastic silencing. And this has been used in some papers that calculate the temporal constraints.
How long time can such a gene be dormant until it can no longer be reactivated? There have been different studies with different approaches that calculated such temporal constraints, and the result differed between 1 million years to maximally 24 million years of silencing of such a gene after 24 million years. Basically, dollar's law holds, and you cannot reactivate such a gene because it would have been deactivated permanently, disrupted in functionality because of genetic noise.
So everything beyond this time frame is prohibited by Dolow's law.
And so we can look into the data if this time constraint is within the realm of possibility in the case of the reactivation of prolax and insects or not. And that's what I also did in my article.
[00:28:14] Speaker B: Yeah. Another thing I liked is you did some quick back of the napkin simple calculations to show how difficult it would be for larval prolegs to develop within the realities of the fossil record. Are scientists across the literature you're reading, are they careful to do similar calculations to what you're doing to check that their scenarios are plausible and compatible with other claims of evolutionary theory?
[00:28:39] Speaker A: Yeah, that's a good question. So, just to show how simple this calculation just is, just a little recapitulation, what I did, I just looked at this mainstream calculations. How long can such a gene be dormant until it can no longer be reactivated? That's this one to 24 million years time frame that I mentioned. And then I compared it with the time that can be estimated, how long this gene for prolax, or pro endyes, rather, must have been deactivated in the case of arthropods. And there you can take data from the fossil record and from molecular clock data, and you come to a result of 128 to 41 million years, depending on the studies you use. So two to five times the time of the maximum time frame that would be allowable for reactivation of the gene. So it basically is impossible in this time frame. And with this new study that I mentioned before, by Montana edal 2019, they made a new dating of the origin of these different groups. And there the activation would have been about 434,000,000 years ago, and the reactivation would be dated to 350,000,000 years ago. So again, many times the maximum time constraint for gene reactivation. So this is not rocket science. This is a very simple calculation that basically everybody with a little bit knowledge of the data can do to test.
Is such a suggested scenario feasible? Is it plausible? Is it consistent with all the data?
But you generally do not find such considerations anywhere in the mainstream literature. And to me, this suggests that evolutionary biologists don't bother to test their hypothesis, because the theory simply implies that dollar's law must have been broken, and therefore it must be possible because it happened so better. Don't let petty arithmetic get in the way of our beautiful, just show stories.
And that's probably the reason why they don't bother to test. They know it must be possible because they simply assume, based on darwinian theory, it must have happened. So it's not necessary to check.
[00:31:12] Speaker B: Yeah, that is a problem. Well, final question, Gunter, for you. Today, the origin of prolegs, as well as the complete metamorphosis seems less surprising on a design hypothesis than an evolutionary one. Indeed, if we were to look at these biological developments from an engineering perspective, we might consider the activation of these functions as part of the planned design constraints built into them from the get go. Would you agree that intelligent design is a better explanation? And what's your reason for that?
[00:31:42] Speaker A: Yeah, definitely. So definitely agree that design is the best explanation for the data. And there are several reasons for this. One is this time problem that the time is too short for an unguided process to evolve metamorphosis. And also the second time problem that this time, where the prolag gene would have been deactivated, is way too long for an reactivation to be feasible. So in both cases, origin of metamorphosis itself and the reactivation of this prolag gene, the evolutionary explanation simply fails. And on the other hand, we know that an intelligent mind can introduce new information quickly to achieve a certain goal. And even according to mainstream experts, if you look at the distribution of the characters, you see, as I already mentioned, that prolags are not homologous in the different groups of holometabolans, but at least originated more than 30 times. So this implies this multiple independent origin of Prolax. And this is also a design signature. If you have this kind of reusing of the same construction in a modular way in different instantiations, this is a hallmark of design engineering and very well resonates with design approaches, for example, like Winston Hewart's dependency graph hypothesis. So in my view, clearly the evolutionary explanation fail for these phenomena, and intelligent design is the best explanation of the data.
[00:33:28] Speaker B: Well, it's one reason I love your work, Gunter, just the reality check that you give to the evolutionary story.
It's a beautiful addition to our work and to the intelligent design community. Well, fascinating discussion as always. We'll leave it there for now. But I want to thank you for your time on this topic, and I look forward to unpacking more of your fossil Friday pieces.
[00:33:50] Speaker A: Sure. It's my pleasure.
[00:33:52] Speaker B: Well, you can read Dr. Beckley's fossil Friday series
[email protected]. That's evolutionnews.org. You'll find this one and dozens of others where he unpacks a lot of great material in a very accessible way to read. Well, thank you, Gunter. Until next time, I'm Andrew McDermott for idthefuture. Thank you for listening.
[00:34:16] Speaker A: Visit
[email protected] and intelligentdesign.org. This program is copyright Discovery Institute and recorded by its center for Science and Culture.
