Is ID falsifiable by any kind of experiment?

Okay, I'll take a stab at this one. Both.An evolving population will have a variety of genes providing diversity within that population. Also individuals within that population will have novel mutations, which may or may not spread through the population. Obviously, those novel mutations are the source of genetic variety. Even a badly bottle-necked population will gradually pick up new mutations. No. Not really.The existence of an evolving population would not on its own necessitate UCA. It would logically mean that a certain amount of common ancestry existed, but it would not, on its own, demonstrate UCA. It would imply UCA, but I don't think that that observation would be enough to prove UCA all on its own. For that you would need further evidence of widespread common descent.Of course, we do have that evidence, so... What? No!In order to provide evidence for common ancestry, you would look at the commonalities between the organisms in question. Think about it; when we compare two people's genes to see if they are related, we look at what they share, not what's different. The fact that There are differences between parents and their children is evidence of random mutation, but the fact of random mutation on its own would not provide incontavertible evidence for UCA.The fact that all living creatures share the same basic genetic code on the other hand, that would count as strong evidence of UCA. I don't think anyone is claiming that. Either you have misunderstood what people are actually claiming or there has been some other miscommunication. I could quibble over the exact phrasing of that but instead I'll just ask; what would you say is the threshold for UCA? What type and level of evidence would you accept as sufficient to accept UCA? What would that look like? Science demands evidence, not proof. Evidence for science, proof for logic and mathematics. I know that this sounds like nit-picking, since the two terms are used interchangeably in everyday parlance, but they have distinct meanings in the philosophy of science and the distinction is important. No scientific theory is ever "proved". The germ theory of disease is not proved. Boyle's law for the expansion of gases is not proved. Rather, they have been backed with evidence to the point where they have been (tentatively) accepted as consensus. I think we all agree on this. These are contentious issues with entrenched opinions on both sides. The only way to avoid this is to hew as closely as possible to the science. What is UCA? What evidence would we expect to see if it were true? Do we see that evidence? What, if any, alternative explanations exist and what evidence would we expect to see from them? How do rival explanations compare in their evidential base and explanatory power?The alternative is to shoot of one or two sentence posts calling someone a big stupid meanie, but I can't really see what anyone would get out of that.Mutate and Survive

You call it "strong" evidence and I get that. Just how can we make this more objective. I know it's hard to put a p-value on this.What alternatives to UCA are we considereing? What would we expect to observe then?Some have been considering one or two or an unspecified few number of distincted common ancestors. Other theories are origins from outer space, creation by intelligence. Last one may be hard to compare as it needs specification on how life could have been created. We would need plausible evolutionary paths with evidencial support for some critical processes in species we see today. These things are often overlooked, as they seem so common. Lets take a look at one example: life cycle of butterflies, transformation to the last stage. We would need an evolutionary path to how this transformation started from the butterfly ancestor. As we see now, pupa's body structure is almost completely incinerated internally, to give way of forming a whole new butterfly appearance.Do you have any plausible path of how this gradually changed in smaller steps from the ancestor without this transformation, upto the butterfly species we see today, in all its varieties?I would lean towards intelligent creation, rather than gradual steps of evolution. Also due to the fact that I would expect a line of gradual evolution to produce more branches, other than just the "fully" completed butterfly species. But it's hard to know what exactly to expect, when it is not clear what intermediate species would be like. What could be in between full transformation (for the butterfly) and no transformation at all (for the butterfly ancestor who at some point starting to evolve towards transformation)?As there are many examples like this, without any plausible intermediates, being as objective as possible, evidence is in favor of intelligent creation over gradual evolution. I don't think it's scientific to cling onto a theory that is not plausible, do you?

quote:

---

We would need plausible evolutionary paths with evidencial support for some critical processes in species we see today.

---

You are free to choose whatever criteria you want, but I don’t think that science should use that one. The existence of unsolved problems - assuming that it is unsolved - is not sufficient to reject an otherwise successful theory. Really you would need a better explanation - one that addressed all the evidence and offered more than an ad hoc explanation for butterfly metamorphosis.I will also note that the evolution of the mammalian jaw was thought to be such a problem, until the intermediate forms were discovered. If we only have a lack of an explanation how can we be sure that it isn’t simply because we don’t have the data that we need to find the answer?

quote:

---

I would lean towards intelligent creation, rather than gradual steps of evolution. Also due to the fact that I would expect a line of gradual evolution to produce more branches, other than just the "fully" completed butterfly species.

---

But we do have more branches. Butterflies are not the only insects that undergo metamorphosis at all. So that is not much of an objection.

quote:

---

As there are many examples like this, without any plausible intermediates, being as objective as possible, evidence is in favor of intelligent creation over gradual evolution.

---

Is it? I don’t think so. Until you provide an explanation that is actually better then I don’t think you can say that. An ad hoc explanation for butterfly metamorphosis that doesn’t explain the data favouring evolution is not worth anything scientifically.

quote:

---

I don't think it's scientific to cling onto a theory that is not plausible, do you?

---

I don’t think that God-of-the-Gaps style arguments are scientific, and that’s what you’re offering. And if the scientists actually working in the field find evolution to be plausible, why should your contrary opinion matter?

This is no more than God of the Gaps. Everything does not have to be explained or understood in order for the TOE to be correct.
You do not put the same criteria on religion or your beliefs.
If you just want to claim "It's Magic", just say so. Discussion over.

Well, you have to understand that personally, I'm not considering any alternatives for my own purposes. I am perfectly content to accept the ToE, UCA and all that. I'm really only in the business of examining such alternatives as others wish to propose in the context of discussions like this. Yeah, that's kind of plausible, but if there were two or more extant lineages, we should see that reflected in the life we observe today. We would expect to see differences like different protein transcription or different energy transfer processes. We don't see that sort of thing. All life uses the same DNA/RNA transcription. All life uses ATP to get energy into the cells, etc. ID proponents like to talk about how incredibly unlikely abiogenesis was. Well, if that's so, the idea that multiple lineages of life emerged using exactly the same chemical processes must be even more astronomically unlikely. There may well have been more than one instance of abiogenesis, but we will almost certainly never know and if it happened, it appears that only one lineage survived.Of course that's looking at it from a mainstream scientific perspective. From a more religious perspective, a lot of Christian creationists propose a different kind of "multiple origins" model; special creation. They propose a model where different created "kinds" were originally made by God and they diversified from there. Something like this; Needless to say, this is not what we see in reality, where all known living things fit into a single tree of life, whether looking at morphology or genetics. The special creation model can be safely considered debunked. That's not really an alternative to UCA. It's actually kind of irrelevant. It doesn't change anything about UCA. Either we have UCA or we don't. The possibility that the first life came from space doesn't really change that. Even the proponents of panspermia - who, it must be noted, are few - typically suggest a single panspermia event with all terrestrial life originating form that. The only difference would be that if panspermia is true we would presumably share common ancestry with whatever life we originally came from, somewhere out in spaaaaace.As I have said before, I have no time for panspermia, I think it's kind of silly. It has very few serious proponents. It sure does!You've hit the nail on the head here. If someone wants to suggest that life was created by an intelligent agent, it immediately begs the question of exactly who this creator was and in the case of "Intelligent Design" types, it's always Yahweh. Oh sure, they will leave open the possibility that it was some nebulous other, but privately, personally, they're always convinced it's the God of the Bible. They often try not to say so of course, because that would give the game away and reveal that they are doing apologetics rather than science and destroy their chances of being taken seriously. The number of entirely secular ID proponents is so small that they can be counted on one hand. So these are extremely muddy waters.Also, I have to point out again that this is not an alternative to UCA. An intelligent creator could have created all life together, thus giving us UCA for all life on Earth. Or they could also have created life in separate batches. They clearly didn't, but they could have, in principle. Like panspermia, this is an alternative to natural abiogenesis, not UCA.So we have two alternatives that are not really alternatives and one - the creationist model - which is trivially easy to falsify with observations like widespread genetic similarities, shared endogenous retroviruses, human chromosome 2, that sort of thing. Okay. Any specific "processes"? Because there are lots of examples of well understood evolutionary pathways. If you will forgive me, this is a poor example to pick. How did butterflies evolve their life-cycle? They got it from their ancestors - moths - who already had that life-cycle. Where did moths get it from? From their ancestors, which are thought to have been closely related to caddis flies, which also have a larval stage of their own. In fact, lots of insects have a larval stage, lots of other animals too. In fact it's ubiquitous and certainly not unique to butterflies. It is an incredibly basal characteristic, emerging in the Cambrian at the most recent. If you want to know how larval forms emerged, you're not going to get there by looking at butterflies.For what it's worth here is the abstract of a paper looking at this;

quote:

---

Origins of the other metazoan body plans: the evolution of larval forms

​

Rudolf A Raff

​

Published:11 January 2008https://doi.org/10.1098/rstb.2007.2237

​

Abstract
Bilaterian animal body plan origins are not solely about adult forms. Most animals have larvae with body plans, ontogenies and ecologies distinct from adults. There are two primary hypotheses for larval origins. The first hypothesis suggests that the first animals were small pelagic forms similar to modern larvae, with adult bilaterian body plans evolved subsequently. The second hypothesis suggests that adult bilaterian body plans evolved first and that larval body plans arose by interpolation of features into direct-developing ontogenies. The two hypotheses have different consequences for understanding parsimony in evolution of larvae and of developmental genetic mechanisms. If primitive metazoans were like modern larvae and distinct adult forms evolved independently, there should be little commonality of patterning genes among adult body plans. However, sharing of patterning genes is observed. If larvae arose by co-option of adult bilaterian-expressed genes into independently evolved larval forms, larvae may show morphological convergence, but with distinct patterning genes, and this is observed. Thus, comparative studies of gene expression support independent origins of larval features. Precambrian and Cambrian embryonic fossils are also consistent with direct development of the adult as being primitive, with planktonic larvae arising during the Cambrian. Larvae have continued to co-opt genes and evolve new features, allowing study of developmental evolution.

---

That's not really a hypothesis available to you. The "gradual steps of evolution" are very real and can be demonstrated in both lab and field. You can suggest a designer, but clearly, that designer left off at some point and evolution took over. You could perhaps dispute how much of the diversity of life is down to evolution, but you can't seriously promote a model which does not include any evolution, because that just isn't consistent with observed reality. That's a puzzling statement. For starters, there are an estimated 174 250 species of Lepidoptera and only 17 950 of them are butterflies. And I'm pretty sure that's just the extant species. With over 150 000 species of moth out there, how many branches do you want? Trichoptera, AKA caddis flies, a sister group to Lepidoptera, number 14 500 species. How many branches do you want? The Endopterygota, the insect superfamily which contains Lepidoptera and Trichoptera, along with many others, all of whose members have a larval stage, number over 1 million species. How many branches do you want?Are you talking about branches in the fossil record? How many do you expect to see? I think we all know that insects fossilise poorly. Lepidoptera do so extremely poorly. Nonetheless, there are fossil Lepidopterans.Also, to speak of ""fully" completed" butterflies is a bit weird. Butterflies are not "complete". No species is. Or all species are, whatever your preference. It's easy to fall into the trap of thinking of extant species as somehow "complete", but really that's just presentism. It just doesn't make sense as a descriptor is what I'm saying. Evolution has no goal, so the only objective sense in which it can ever be "finished" is when a lineage goes extinct. A good 500 million years or so of evolution would lie between butterflies and the first emergence of larval forms. So you're casting this particular net a bit wide. There are butterfly and moth fossils and we have an idea of what the most basal Lepidoptera looked like, but none of that is going to address the origins of larval forms. But that would mean ignoring the evolutionary pathways for which we do have good evidence and proposing a "designer" for which we have absolutely no evidence whatsoever. That seems like a massive breach of parsimony. Everyone agrees with this in principle. In practice however, I don't find either UCA or the ToE implausible and critics of evolution have, over the years, failed to make a convincing case against them.Mutate and Survive

Sensei's post limit has been removed.

ChatGPT may be the nail in the coffin for places like theseThe theory of universal common descent proposes that all living organisms on Earth share a common ancestry, meaning that they are ultimately descended from a single common ancestor. This concept is supported by various lines of evidence from different scientific fields. Here are some key pieces of evidence for universal common descent:Fossil Record: The fossil record provides evidence of extinct species that showcase the gradual transition and evolution of life forms over millions of years. Fossils of intermediate forms, such as the well-known examples of transitional fossils like Archaeopteryx (showing characteristics of both dinosaurs and birds) and Tiktaalik (representing a transitional form between fish and tetrapods), provide evidence of common ancestry.Comparative Anatomy: The study of comparative anatomy reveals similarities in the anatomical structures of different species. Homologous structures, which are features that have a common origin but may serve different functions in different organisms, suggest a shared ancestry. Examples include the pentadactyl limb structure found in mammals, reptiles, and birds, and the similar bone structure in the flippers of whales and the limbs of land mammals.Embryological Development: Comparative embryology examines the development of embryos across different species. Similarities in early developmental stages, such as the presence of gill slits in vertebrate embryos or the formation of similar structures during early development, support the idea of common ancestry.Genetic and Molecular Evidence: Advances in genetics and molecular biology have provided strong evidence for universal common descent. DNA sequencing has revealed genetic similarities between different organisms. The genetic code, which is nearly universal across all organisms, suggests a common origin. Additionally, the presence of pseudogenes (non-functional remnants of genes) and shared genetic markers across species further support the concept of common ancestry.Phylogenetic Analysis: Phylogenetic analysis involves constructing evolutionary trees based on shared characteristics or genetic sequences. These trees depict the relationships between different species and their common ancestors. By analyzing the similarities and differences in traits or genetic sequences, scientists can infer evolutionary relationships and trace back to a common ancestor.It's important to note that these pieces of evidence, along with many others, have been extensively studied and corroborated by multiple lines of scientific research. Universal common descent remains the prevailing scientific explanation for the diversity of life on Earth, supported by a vast body of evidence from various scientific disciplines.

It's another avenue, yes.Of course - Wiki pages have had that data stored on them for years (decades?) now. That didn't seem to do much.I'm starting to think that places like these (EvC) aren't around as an information hub - those looking for information will find it easier and faster just by using Google or other available methods.
I think we're still here because of the people who are convinced they're right despite all the information in their face to the contrary.
To such people - ChatGPT being just one more place filled with "the wrong interpreation of the same data..." is just one more place to ignore....Maybe?

Yes, I agree. That is why UCA seems to be the only viable option for science to consider. If UCA fails, we need to reconsider our origins. We have branches of species with larvae gradually changing into their adult form, and branches of species where larvae/caterpillars that completely rid of their larvae form to grow their adult appearance. So I would expect to find many species in between, or at least some branches originating from these intermediate species. Or would you suggest it was fast evolution without many intermediate steps, instead of a gradual evolutionary process that took millions of years or longer with many intermediate species?

Even though everyone on the planet is descended from a single man or woman, that man and that woman (who did not live contemporaneously) were not the first man or woman, and there were many other people alive at the same time. They just happened to be the only man and woman who left descendants alive today.In the same way, UCA was not the first life. It lived within a thriving community of life, probably widely varied with many species and genuses and so on. It was just the only life that left descendants.For there to be multiple UCAs there would had to have been more than one independent origin of life. This is certainly possible, but only one of these origins of life left modern descendants given the relatedness of all life today.But let's say that UCA fails, that we find a branch of life that is unrelated to all other branches of life. That wouldn't cause us to "reconsider our origins" in any significant way. It would a fascinating discovery, but also a kind of shrug, as in, "Oh, life originated more than once - figures." In fact, it would make sense that on the early planet life began and failed multiple times before finally persisting, and that life originated and persisted more than once is not a terribly novel thought.If there were multiple occurrences of the "first life" then just as early humans apparently outcompeted and drove extinct all other hominid species, it is likely that some "first life" was more competitive than other "first life" and drove it extinct, explaining why we have so far detected only one UCA.By "reconsider our origins" did you mean we should consider religious explanations? No scientific puzzle has ever resolved to a religious answer, so why would the origin of life be the first? You don't think other scientific puzzles should consider religious answers, do you, such as unifying quantum theory (the theory of the very small) and relativity (the theory of the very large)? The term "intermediate species" can be misleading because it implies a species is in a transitional state from one species to another. The reality is that no species is fixed or permanent. They're all transitional. We drive stakes in the ground that we call species. Any life currently alive we call a species, and any fossil type that is plentiful in the fossil record we also tend to call a species, but those fixed points that we choose occur on long lines of change, and picking any particular point on that line and calling it a species is arbitrary. Every point on that line represents a fully formed species that is also in a state of change. There is no species in the history of life that remained the same species forever. It gradually evolved and changed or went extinct. Change is impossible to prevent, for even if the environmental pressures remained static there would still be drift since almost every reproductive event includes mutations.--Percy

quote:

---

If UCA fails, we need to reconsider our origins.
​

---

UCA is not about to fail. Even if we accepted your butterfly argument and even if we accepted it pointed to an intelligent designer why would we conclude that butterflies were an individual creation? Surely it would make more sense to assume that the designer worked by using genetic engineering to modify a moth.

quote:

---

We have branches of species with larvae gradually changing into their adult form, and branches of species where larvae/caterpillars that completely rid of their larvae form to grow their adult appearance

---

We have species of insects where the juveniles are simply smaller adults.We have species of insects where the adult (imago) stage is notably different from the juvenile (nymph), but do not undergo complete metamorphosis.For some of those species of insects the form that emerges from the eggs (pro-nymph) is different from the nymph.Of the species of insects that pupate we have some which start the transformation to adult form before entering the pupa stage (silkworm larvae have the beginnings of wings).It seems that we do have adequate intermediates, allowing for the timescales involved.Current thinking - which is not hard to find - is that the larva is a development of the pro-nymph and the pupa is a development of the nymph.

Well, every ancestor of a common ancestor is still a common ancestor. So the first biological cell should be a UCA. Or there had been multiple events where a biological cell formed.Now consider this: the mutation rate in unicellular eukaryotes (and bacteria) is roughly 0.003 mutations per genome per cell generation. So any living unicell would produce around 300 exact clones on average before producing one mutated cell.Unicells capable of surviving and succelfully multplying, would leave many offspring around, unaltered and unchanged, populating the whole globe. What's stopping them?We should be able to find many unicell species from the beginning, that are plausible ancestors of plants as well as animals and fungi and insects, with indications that they are clones of the same UCA cell.But guess what. We find nothing of such type! UCA fails for sure.Even if mutation rates where 10 times higher in earlier days. Cells would still procuce 30 times more exact clones than mutated ones. The exact clones would always remain in majority, if all cells keep multiplying. No extinction event would wipe out the whole globe to rid it from all of the unicell species of the first era.So again, looking at data objectively, UCA is not very plausible.

Your argument assumes the availability of unlimited resources, and the absence of environmental hazards that might have driven the UCA to extinction. Neither assumption is very plausible, according,y it is your argument that should be rejected.

I apologize that we were confusing. Granny Magda shortened LUCA to UCA, I don't know why. We're actually talking about the Last Universal Common Ancestor, also known as the Most Recent Common Ancestor. dwise1 introduced the proper term, LUCA, prior to that back in Message 475. Those are reasonable numbers, but what's more important is the number of mutations per generation in a population. So with a population size of 1 there would be only 0.003 mutations per generation, but with a population size of a trillion there would be 3 billion mutations per generation.Is a trillion a reasonable size for a bacteria population, say a staph infection? If one bacterium weighs 10^-12 grams, then a trillion of them weighs one gram. Did you know that that only 10% of our bodies are human cells? The other 90% of cells are bacteria (bacteria are much smaller than human cells and represent a small percentage of our total weight or volume).The average human being carries more than a quadrillion bacteria (closer to a hundred quadrillion, but let's use the smaller figure to make it more difficult for me to make my case). If we use a very slow bacterial replication rate of one generation per hour then 3 billion mutated bacteria are created in your body every hour, or 72 billion per day. Is that enough mutations for you? In just your body alone? And with 8 billion people in the world that's 5.8 × 10²⁰ bacterial mutations per day just within human bodies alone.And humans are only a tiny percentage of the total biomass of the earth, so there's all the bacteria in all the other animals, then there's all the bacteria in plants, and then there's all the bacteria that live outside other life. I won't even try to guess how many bacteria that there are in the world, but safe to say that an astoundingly huge number of newly mutated bacteria appear every day.An example of an effectively evolving bacteria is the tuberculosis bacteria. There are quadrillions and quadrillions of them throughout the world creating enormous numbers of mutations, usually SNP's, that occasionally have better success in certain kinds of environments, such as in the presence of tuberculosis drugs. There are now some strains of tuberculosis that are resistant to all currently available drugs. And this despite just 0.003 mutations per generation, or probably less since the mutation rate of the tuberculosis bacteria is low for bacteria.Multicellular organisms tend to have much larger genomes than bacteria, and they produce many more mutations per reproductive event. For instance it is estimated that the average human baby has around 75 mutations (you'll see different estimates cited - when I look this up I typically find numbers ranging from 40 to 100). Of course our generation time is very long, so we evolve much more slowly than bacteria. Unicellular life does age, but many bacteria are effectively immortal except that they have to compete for resources just like all life. For example, ask yourself what happens to gut bacteria when the host animal dies? The environment where they formerly flourished is gone and they eventually die. Or what happens when the small pool of water that was the bacteria's home dries up. They die. I think it very unlikely that any LUCA clones could have survived until today. Even if at one time the ancient earth held quadrillions and quintillions and sextillions of LUCA clones, environmental conditions have changed dramatically since then and would be unlikely to favor the survival of that life. But why do you think the presence or absence of LUCA clones today support your position? Certainly if we found some (I don't know how we'd know we had one even if it were sitting under our microscope) it would be an astounding discovery but not particularly germane to the argument you're trying to make. Any mutations that happened to be beneficial, which some mutations will be, would provide a survival advantage for their cells, enabling them to outcompete other cells, eventually replacing them. We actually witnessed this process of beneficial mutations outcompeting the unmutated versions with the covid virus. Delta outcompeted and replaced the original virus, omicron outcompeted and replaced delta, and BA.1 and BA.2 outcompeted and replaced omicron, and there have been subsequent ones that replaced BA.1 and BA.2. Again, I think we should be using the term LUCA. Given the information I've provided, what do you think now?--Percy

But you haven't provided any viable alternative. You mentioned two ideas that are not alternatives and one that has been thoroughly debunked. If you want to topple common descent, you'll have to provide an observation that completely falsifies it, or provide a model that better explains the data. Preferably both. You don't seem to have either. What do you mean "find"? Do you mean amongst extant species? Why would you expect that? There's no guarantee that any given intermediate should survive, most species become extinct. Anyway, as PaulK mentioned, there are a wide variety of larval forms with many variations on exactly how they function. We have insects that undergo no metamorphosis, some that undergo incomplete metamorphosis and some that undergo full metamorphosis. Even amongst those insects that undergo full metamorphosis there are various different ways of going about it.Do you mean in the fossil record? You know perfectly well that things like caterpillars are going to leave relatively little in the way of fossils. Nonetheless, we do have fossils of early insects. They start out simple, with young looking more or less like tiny adults, as per modern silverfish. Incomplete metamorphosis emerges next, followed by complete metamorphosis. To me, that looks like what we might expect to see in the fossil record under the standard evolutionary model.Also, it's not as if researchers are clueless when it comes to the evolution of full metamorphosis. This article from Scientific American gives a good run down;

quote:

---

Complete metamorphosis likely evolved out of incomplete metamorphosis. The oldest fossilized insects developed much like modern ametabolous and hemimetabolous insects—their young looked like adults. Fossils dating to 280 million years ago, however, record the emergence of a different developmental process. Around this time, some insects began to hatch from their eggs not as minuscule adults, but as wormlike critters with plump bodies and many tiny legs. In Illinois, for example, paleontologists unearthed a young insect that looks like a cross between a caterpillar and a cricket, with long hairs coating its body. It lived in a tropical environment and likely rummaged through leaf litter for food.

​

Biologists have not definitively determined how or why some insects began to hatch in a larval form, but Lynn Riddiford and James Truman, formerly of the University of Washington in Seattle, have constructed one of the most comprehensive theories. They point out that insects that mature through incomplete metamorphosis pass through a brief stage of life before becoming nymphs—the pro-nymphal stage, in which insects look and behave differently from their true nymphal forms. Some insects transition from pro-nymphs to nymphs while still in the egg; others remain pro-nymphs for anywhere from mere minutes to a few days after hatching.

​

Perhaps this pro-nymphal stage, Riddiford and Truman suggest, evolved into the larval stage of complete metamorphosis. Perhaps 280 million years ago, through a chance mutation, some pro-nymphs failed to absorb all the yolk in their eggs, leaving a precious resource unused. In response to this unfavorable situation, some pro-nymphs gained a new talent: the ability to actively feed, to slurp up the extra yolk, while still inside the egg. If such pro-nymphs emerged from their eggs before they reached the nymphal stage, they would have been able to continue feeding themselves in the outside world. Over the generations, these infant insects may have remained in a protracted pro-nymphal stage for longer and longer periods of time, growing wormier all the while and specializing in diets that differed from those of their adult selves—consuming fruits and leaves, rather than nectar or other smaller insects. Eventually these prepubescent pro-nymphs became full-fledged larvae that resembled modern caterpillars. In this way, the larval stage of complete metamorphosis corresponds to the pro-nymphal stage of incomplete metamorphosis. The pupal stage arose later as a kind of condensed nymphal phase that catapulted the wriggly larvae into their sexually active winged adult forms.

​

Some anatomical, hormonal and genetic evidence supports this evolutionary scenario. Anatomically, pro-nymphs have a fair amount in common with the larvas of insects that undergo complete metamorphosis: they both have soft bodies, lack scaly armor and possess immature nervous systems. A gene named broad is essential for the pupal stage of complete metamorphosis. If you knock out this gene, a caterpillar never forms a pupa and fails to become a butterfly. The same gene is important for molting during the nymphal stage of incomplete metamorphosis, corroborating the equivalence of nymph and pupa. Likewise, both pro-nymphs and larvae have high levels of juvenile hormone, which is known to suppress the development of adult features. In insects that undergo incomplete metamorphosis, levels of juvenile hormone dip before the pro-nymph molts into the nymph; in complete metamorphosis, however, juvenile hormone continues to flood the larva's body until just before it pupates. The evolution of incomplete metamorphosis into complete metamorphosis likely involved a genetic tweak that bathed the embryo in juvenile hormone sooner than usual and kept levels of the hormone high for an unusually long time.

---

Sounds reasonable to me. Certainly more reasonable than the completely unsupported notion that some kind of "intelligent designer" (read: deity) came along and interfered with insect evolution multiple times. I would suggest that we listen to the people who study these things professionally. Why would I even have a personal opinion on a subject like that? As far as I am concerned I don't have sufficient expertise to be entitled to an opinion on the matter.Mutate and Survive