About the SA Blog Network



Opinion, arguments & analyses from the editors of Scientific American
Observations HomeAboutContact

Controversial caterpillar-evolution study formally rebutted

The views expressed are those of the author and are not necessarily those of Scientific American.

Email   PrintPrint

Butterfly metamorphosis from caterpillarA contentious paper suggesting that butterflies and caterpillars descended from different ancestors has been rebutted in the same journal in which the original, controversial research appeared.

In August, retired biologist Donald Williamson of the University of Liverpool in England posited in an online Proceedings of the National Academy of Sciences USA (PNAS) paper that the metamorphosis between caterpillars and butterflies stems from a past cross-breeding between butterfly ancestors and those of velvet worms. "I reject the Darwinian assumption that larvae and their adults evolved from a single common ancestor," Williamson wrote.

The paper drew a great deal of fire, both for its assertions (which one developmental biologist said were better suited to the "National Enquirer than the National Academy") and for its backdoor acceptance for publication. Williamson’s study arrived in PNAS as a "communicated submission," in which a member of the National Academy of Sciences submits the paper on the author’s behalf and handpicks its peer reviewers. A high-placed advocate, then, can essentially knock down for an ally some of the tallest hurdles in peer-reviewed publishing. In Williamson’s case, academy member Lynn Margulis of the University of Massachusetts Amherst had ushered the research into the journal.

In August, when Williamson’s paper was published, Margulis told Scientific American that she needed "6 or 7" peer reviews to secure the "2 or 3" positive responses needed to present the work for publication. That statement set off a cascade of criticism of PNAS‘s two-tiered submission process and, according to Nature News, led the journal’s editor in chief to write to Margulis demanding "a satisfactory explanation for [her] apparent selective communication of reviews." Her reply, obtained by Nature News, explained that three researchers had declined for scheduling reasons or lack of expertise, and two were omitted from the official PNAS submission because they lacked formal credentials.

Now PNAS has published a rebuttal to the hybridization paper. In direct response to Williamson’s paper, "Caterpillars evolved from onychophorans by hybridogenesis," biologists Michael Hart of Simon Fraser University and Richard Grosberg of the University of California, Davis, published a study entitled "Caterpillars did not evolve from onychophorans by hybridogenesis." (The latter paper was not a communicated submission.)

Hart and Grosberg call Williamson’s claim "astonishing and unfounded," asserting that data in the scientific literature show no genetic basis for his theory or its implications. For instance, they write, "all of the available phylogenetic tests strongly reject" Williamson’s hypothesis that insects with caterpillar stages would contain a package of genes from the velvet worm.

Further, Hart and Grosberg add, Williamson’s prediction that metamorphosing insects—the recipients of the hybridization genes—would have larger genomes than the donor velvet worms "is easily rejected": one velvet worm species, in fact, has a larger genome than is known for almost any other insect. The genome size data, they write, "are not merely inconsistent with Williamson’s hypothesis but directly contradict its simplest predictions."

It remains to be seen whether the appearance of the new paper appeases some of the harshest critics of Williamson and PNAS—evolutionary biologist Jerry Coyne of the University of Chicago pondered in his blog whether the controversial work was the worst paper of the year and bemoaned "bigwigs" pushing "substandard work into publication."

As for the backdoor path to publication, PNAS announced in September that the communicated-submission system will be terminated next year but maintained to Nature News that the Williamson uproar had nothing to do with the decision.

Illustration of butterfly metamorphosis: Wikimedia Commons

Rights & Permissions

Comments 19 Comments

Add Comment
  1. 1. VMartin1 1:42 pm 10/29/2009

    Darwinians make obviosly a great fuss regarding their peer-reviewed journals. They think that darwinism is a science – and publishing their bizarre hypothesis in peer-reviewed is the only argument they have to back up such idea. Argumets done by their opponents are heavily neglected.

    Link to this
  2. 2. hotblack 2:38 pm 10/29/2009

    Martin, when you lack knowledge on something, making bold statements that the thing therefore doesn’t exist is a revealing response. If you seek knowledge, there are mountains of books that contain the factual information you lack. If you aren’t seeking knowledge, then what is this you’re doing?

    Link to this
  3. 3. calevenice 4:23 pm 10/29/2009

    I agree with martin on this issue. Although the controversial paper in question is probably wrong, it would be rejected by the scientific (especially Biology) community even if it was right. I will have to admit that Darwinians (to use Martin’s label to refer to the majority of Biologist) are the most arrogant people I have dealt with in the scientific community.

    Link to this
  4. 4. Dimitris 5:33 pm 10/29/2009

    How exactly do you disagree with "darwinians"? Doesn’t evolution of the fittest lead to competition and eventually evolution? Don’t species give birth to new species, under certain conditions?

    Link to this
  5. 5. robert schmidt 6:26 pm 10/29/2009

    @calevenice & VMartin1, and creationists are some of the most ignorant people I have ever met. They speak as though they have absolute authority about something they haven’t read one authoritative work on. They use every fallacy in the book to promote a primitive superstition, demonstrating that not only do they lack any knowledge on the subject but that they also lack any form of intellectual process. Having our world view determined by a dictator, in this case a high ranking member of a church/sect seems to be what we fought the Second World War and the Cold War to prevent. Well, I guess most people are happy enough to believe in a lie, as long as the lie works in their favour. If a person’s impatient with your simple mindedness comes off as arrogance then so be it. Perhaps if you had some clue what you were talking about and didn’t spout tired old arguments that were refuted decades ago people would treat you more like an adult.

    Link to this
  6. 6. zuluqueen 2:54 pm 10/30/2009

    I think it best that creationists defer from posting their ignorant comments on this issue. This is a science journal, not an ID blog.

    Link to this
  7. 7. zuluqueen 4:24 pm 10/30/2009

    I think it best that creationists defer from posting their ignorant comments on this issue. This is a science journal, not an ID blog.

    Link to this
  8. 8. TomBuckner 12:23 am 10/31/2009

    Correction needed in this article:

    Link to this
  9. 9. TomBuckner 12:42 am 10/31/2009

    Oops, didn’t know that last comment would go prematurely. Again:

    Correction needed in this article: John Matson writes "one velvet worm species, in fact, has a larger genome than is known for almost any other insect."

    Onychophorans are not classified as insects; they are not even classified as arthropods! They belong to a separate phylum, Onychophora, a sister group to Arthropoda. Even scorpions and crabs have closer ties with butterflies than do the velvet worms.

    I can understand why Williamson might have been emboldened to publish a paper like the one in question as it appears that hybridization may occasionally work after all ( see for example which even hints at the present controversial idea) but it’s harder to see why he’d not have investigated the available genomic data for butterflies and onychophorans first.

    Link to this
  10. 10. 3:28 pm 11/1/2009

    there is no such a thing as human evolution

    think about it, if everything came from one cell, then where did that cell come from? Life has to be created

    Link to this
  11. 11. robert schmidt 6:19 pm 11/1/2009

    @ufoInsurance, I don’t know how many times I’ve said it; instead of making an idiotic statements why don’t you actually do a little research. There have been numerous articles here on the subject. I don’t know why you think you’ve found a hole in the science when you haven’t even read one book.

    Link to this
  12. 12. coolmoss 4:50 pm 11/2/2009

    I hardly think that this can be interpreted as favouritism within the scientific community toward evolutionists, especially considering that Margulis is responsible for endosymbiosis; a very strong example of co evolutionary mutualism. In fact it is a wonderful demonstration of peer review.
    By contrast, when was the last time that a christian was criticized for not having the sense to ask for a little proof that Christ rose from the dead?
    When was the last time a chirstian was scrutinized by fellow christians for shabby evidence and mere testimony?

    No no no, in fact this is what separates science from religion. This is the shit.

    Link to this
  13. 13. living fossil 11:57 pm 11/2/2009

    @ calevenice – Probably not. All the rant about "darwinians" is rant against a caricature of the mainstream scientists, who supposedly defend a no less caricatural "darwinian orthodoxy" in which everything, no matter what, is ignored but a brute fight for survival. They supposedly ignore embriology, the nature of variation, hybrids, commensalism, varying rates of mutation, etc (if we’re lucky; it could include really crazy phylogenies not "simply based on DNA", ETs, deities, mystical energies, or worse), whatever someone intends to purport as the new revolution in the understanding of biodiversity. Some of these things may be very relevant (from the ones that really exist), but alone, any of them is enough to account for the origin of adaptation, whereas natural selection just needs hereditary variation relevant for the trait in question, with their respective fitness differentials. As long as people do not fall on the traps of pan-adaptationism and sloppy just so stories, there’s only very technical and almost boring details to be discussed, and its importance can’t be denied. All the other things, they are indeed very interesting, perhaps even more (that’s what I usually think), and may be really, really important (as they mostly deal about the proper material of selection and its workings, rather than just the body count), but unlikely to be a real "alternative" to natural selection or to meaningfully diminish its importance.

    Link to this
  14. 14. living fossil 12:15 am 11/3/2009

    @ VMartin1 – your blog seems to be very interesting after a very brief examination – seems that it’s not creationist or some wacky "alternative" to mainstream with mystical energies and this sort of thing. It seems to just nail some pan-adaptationist or selectionist assumptions, which is quite interesting and valid.

    However, while I think that a more complete picture of biology and evolution, taking in consideration all that there is to be studied over the nature of variation, ecological interactions, hybridization and what not, away from selectionism and pan-adaptationism, I think that it is a mistake to downplay the role of natural selection in the origin of adaptation, and to disdain the peer review process. By doing that, I think you’re more likely to be ignored and ridiculed than to actually bring serious attention to other important, and often more interesting, aspects of biology.

    Link to this
  15. 15. SteveO 1:53 pm 11/3/2009

    It is clear that evolution is a fact, and that our current understanding of the various ways it happens are getting very close to the truth. There is so much evidence for this. If those who are religious base their faith on whether evolution is true or not, they have a very shaky basis for their faith indeed. There is nothing inherently contradictory about faith and evolution (ask the Pope for example) any more than the theory of relativity should contradict faith. On the other hand, if your faith denies reality, well then that becomes pathological. To paraphrase Sancho Panza, in such a case, whether your faith hits reality or reality hits your faith, its going to be bad for your faith.

    To the article point, though, while it is now shown that the initial paper’s hypothesis was incorrect (and really, velvet worms? sheesh), I have to admit given what I know about how butterflies (and other metamorphosing adult forms) develop from their larval precursors, I have wondered if an ancient caterpillar was parasitized by an ancient butterfly.

    The caterpillar carries imaginal disks within its body. The caterpillar is driven to be a feeding machine, and once gorged on its food, it spins a cocoon or chrysalis. Then, pretty much its entire body – including organs – dissolves. The imaginal discs then use this caterpillar "soup" to build the adult form. Why dissolve the organs when the adult could use or modify them?

    Given the amazing ways that parasites control their hosts (e.g. I think it is a reasonable hypothesis to test to see if the butterfly is the ultimate parasite on the lowly caterpillar.

    Any good hypothesis should be testable, so I would love to know if anyone has tested to see if the imaginal discs and the caterpillar genomes are actually different and support this. The sum total of genes would not necessarily be more than a non-metamorphosing animal – many fully adapted parasites have much reduced genomes since their host provides for them. And in such a complete case of parasitism, even the former caterpillar’s genome could have been reduced.

    A beautiful (if gruesome) example of parasitic co-evolution.

    Anyone know enough about the genetics of butterflies to let me know if this is possible?

    Link to this
  16. 16. WaWaKnows 12:34 pm 11/5/2009

    Great question, this is the one question I always ask my biology teachers just to see the looks on their face. I assume the question you are asking is "What was the origin of the first cell that spouted the cells we see today?", or something along those lines.

    Is it so hard to believe that the harsh conditions on Earth 4.6+ billion years ago help aid in the first formation of organic molecules to form a cell like structure?


    Link to this
  17. 17. dhinds 9:01 pm 04/9/2010

    To answer Dimitris:

    "How exactly do you disagree with "darwinians"?

    Darwinians believe that "natural selection" (competition) is the principle force driving evolution. However: Lynn Margulis has demonstrated that the most significant evolutionary leaps were a result of the association of two distinct species (i.e., eukayotes were derived from two prokaryotes with distinct capacities, both of which retained their original genetic structures when contained within a single nucleated cell).

    "Doesn’t evolution of the fittest lead to competition and eventually evolution?"

    Not exactly. Natural Selection is only part of the story.

    Don’t species give birth to new species, under certain conditions?

    Only when they fuse, as in Serial Endosymbiotic Theory, the validity of which has been amply demonstrated. (See Acquiring Genomes: A Theory of the Origin of Species, by Lynn Margulis and her son Dorian Sagan, Basic Books 2002).

    (I have no opinion with respect to Williamson’s paper and haven’t read it).

    Douglas Hinds

    Link to this
  18. 18. dhinds 9:55 pm 04/9/2010

    I just read Williamson’s paper and IMO he made a valid point: The existence of two separate genomes within the same organisms suggests a recurrence of the same kind of historic event that led to the presence of mitochondria within cells whose nuclei contains the DNA of a distinct (and obviously now complementary) organism.

    Furthermore, Williamson called for testing the hypothesis he posed! What could be more objective and scientific than that?

    The hew and cry that’s ensued from this interchange of opinions and perceptions suggests that somebody’s dogma is being questioned and that the scientific powers that be don’t like their assumptions to be challenged.

    Lynn’s Serial Endosymbiotic Theory (SET) was subject to ridicule for many years before the DNA demonstrated the validity of her claims: Human mitochondria has a bacterial origin!

    Charles Darwin (of course) lacked access to the tools that have clearly proved Lynn Margulis’ claims, but I wonder why so many living biologists seem unable to assimilate her discoveries (well actually, she demonstrated the validity of interpretations made by earlier Russian Scientists).

    An eminent geneticist friend of mine in Canada once said when asked whether he subscribed to Lynn Margulis’ SET:
    "I subscribe to whatever Lynn Margulis wants!"

    (I didn’t know at the time that he had worked with her).

    His reply displays a relationship of trust acheived by two oustanding human beings and personally, I’m very glad they both exist.

    Douglas Hinds

    Link to this
  19. 19. dhinds 10:23 pm 04/9/2010

    I strongly recommend to anyone interested in this theme – read the following:


    "Gaia Is a Tough Bitch"

    Richard Dawkins: I greatly admire Lynn Margulis’s sheer courage and stamina in sticking by the endosymbiosis theory, and carrying it through from being an unorthodoxy to an orthodoxy. I’m referring to the theory that the eukaryotic cell is a symbiotic union of primitive prokaryotic cells. This is one of the great achievements of twentieth-century evolutionary biology, and I greatly admire her for it.

    Lynn Margulis: At any fine museum of natural history — say, in New York, Cleveland, or Paris — the visitor will find a hall of ancient life, a display of evolution that begins with the trilobite fossils and passes by giant nautiloids, dinosaurs, cave bears, and other extinct animals fascinating to children. Evolutionists have been preoccupied with the history of animal life in the last five hundred million years. But we now know that life itself evolved much earlier than that. The fossil record begins nearly four thousand million years ago! Until the 1960s, scientists ignored fossil evidence for the evolution of life, because it was uninterpretable.

    I work in evolutionary biology, but with cells and microorganisms. Richard Dawkins, John Maynard Smith, George Williams, Richard Lewontin, Niles Eldredge, and Stephen Jay Gould all come out of the zoological tradition, which suggests to me that, in the words of our colleague Simon Robson, they deal with a data set some three billion years out of date. Eldredge and Gould and their many colleagues tend to codify an incredible ignorance of where the real action is in evolution, as they limit the domain of interest to animals — including, of course, people. All very interesting, but animals are very tardy on the evolutionary scene, and they give us little real insight into the major sources of evolution’s creativity. It’s as if you wrote a four-volume tome supposedly on world history but beginning in the year 1800 at Fort Dearborn and the founding of Chicago. You might be entirely correct about the nineteenth-century transformation of Fort Dearborn into a thriving lakeside metropolis, but it would hardly be world history.

    By "codifying ignorance" I refer in part to the fact that they miss four out of the five kingdoms of life. Animals are only one of these kingdoms. They miss bacteria, protoctista, fungi, and plants. They take a small and interesting chapter in the book of evolution and extrapolate it into the entire encyclopedia of life. Skewed and limited in their perspective, they are not wrong so much as grossly uninformed.

    Of what are they ignorant? Chemistry, primarily, because the language of evolutionary biology is the language of chemistry, and most of them ignore chemistry.

    Link to this

Add a Comment
You must sign in or register as a member to submit a comment.

More from Scientific American

Email this Article