HOPEFUL MONSTER A prestigious journal has published a dubious theory that millions of years ago the velvet worm bred with an insect creating the butterfly's characteristic caterpillar larvae
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Caterpillars transform into butterflies and moths via a radical process known as metamorphosis, where their bodies virtually turn to soup and develop anew.
Since Darwin, biologists have believed that the larval and the adult forms of insects evolved from a common ancestor. Indeed, the evolution of metamorphosis is thought to have fueled the incredible diversity of insects today, allowing them to exploit different habitats at different life stages.
Now, a lone scientist claims that the phenomenon arose when two very different creatures accidentally mated.
In the current issue of Proceedings of the National Academy of Sciences (PNAS), Donald Williamson, a wheelchair-bound 87-year-old zoologist from the University of Liverpool in England, suggests that the ancestors of modern butterflies mistakenly fertilized their eggs with sperm from velvet worms, also known as onychophorans. "People have been trying to find one solution that covers all of metamorphosis," Williamson says. "I say it's a change in taxon during development."
Velvet worms, which fall between worms and insects on the tree of life, have soft-bodies and superficially resemble caterpillars, particularly the larvae of an early butterfly relative known as Micropterix. Velvet worms have evolved a variety of elaborate fertilization procedures. Males are known to place sperm packets not on the female's genital opening, but rather on skin tissue, which the sperm penetrates before migrating to the ovaries.
Williamson believes that an ancient insect accidentally picked up that sperm, and butterflies now contain two developmental programs so they live half their life as velvet worms and half their life as winged butterflies.
"Animals have been able to hybridize since they invented sex," Williamson says. "With external fertilization, there's always the possibility that some sperm will fertilize the wrong egg."
However, scientists asked to comment on Williamson's theory were taken back by it and surprised it made it into such a prestigious journal. For example, from insect paleontologist Conrad Labandeira of the Smithsonian National Museum of Natural History in Washington, D.C.: "You're kidding!"
After looking over the paper, Labandeira pointed out more substantial criticisms. Hybridization between closely related species sometimes occurs in the animal kingdom, but it is highly unlikely that the sperm of a velvet worm could fertilize a distantly related insect egg and produce a viable embryo. He also raises the question of where the genetic program controlling metamorphosis would come from.
"If I was reviewing [this paper] I would probably opt to reject it," he says, "but I'm not saying it's a bad thing that this is published. What it may do is broaden the discussion on how metamorphosis works and…[on]…the origin of these very radical life cycles."
Insect developmental biologist Fred Nijhout of Duke University took a less diplomatic view of the article saying it would be better suited for the "National Enquirer than the National Academy."
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21 Comments
Add CommentAstonishing.
Reply | Report Abuse | Link to thisIf he had 20 years to develop the theory, surely he could have put the time to good use by examining the monumental collection of developmental and genetic evidence that has elucidated the evolution of the arthropods. Instead, he and Margulis apparently used the time to play reviewers off against each other. While Margulis may have good reason to harbour a certain disdain for critics of unconventional theories, it would seem she has developed a disdain for the scientific process and the use of evidence to back up wild claims.
It is an irony that while top journals such as Nature, Science, and Cell call for an overhaul of the modern review process, the National Academy of Sciences remains firmly entrenched in the 19th century. It is depressing how many articles in this journal are published because of blatant biases of the editors, and even more depressing that the journal makes no effort to hide its impropriety.
On the biology side, I have not yet read this article, but I'm guessing it makes no mention of the massive and sudden innovations that would have had to occur, and particularly the invention of pupal stages. Pupal insects undergo nearly complete histolysation of their muscle tissue. To 'stitch' together two organisms into separate life histories would require intelligently designing an organism to suddenly gain the ability to coordinate all these new genes at critical times, in precisely the correct sequence. This theory makes a mockery of the entire field of evo-devo (evolutionary developmental biology).
Astonishing.
I agree with the last bit of dskan, the molecular mechanics of such a fusion are mind bogling and almost inconceivable. It is very highly unlikely of two so different organisms to cross-fertilise and the offspring to be viable, much less fertile.
Reply | Report Abuse | Link to thisHaving said that, I feel like playing devil's advocate. This novel theory comes from someone with relevant professional experience, so I think it deserves to be considered. If a plausible molecular mechanism can be described and tested to see if it is physically possible, then I think the findings should not be discarded. Of course, the burden of proof lies on Dr. Williamson, and extraordinary claims require extraordinary evidence, which so far seems to be missing.
Yes, a velvet worm does look like a caterpillar. Butterflies and flies are both insects and both undergo metamorphosis. They have a common ancestor that developed metamorphosis. A velvet worm does not look like a maggot, nor does a velvet worm look like other insect larvae that are not “caterpillars”.
Reply | Report Abuse | Link to thisThe above debunks the theory on the same level that it was invented.
The described day-dream theory is abhorrent that it has made a peer-review journal. This is not an exercise of biology, but one for the socialists. Has this activity broken any laws?
The "caterpillar" in the accompanying photograph doesn't look like a lepidopteran larva to me. Looks like a Peripatus, perhaps from New Zealand. Now, isn't that an interesting interspecific error!
Reply | Report Abuse | Link to thisAh, the perils of using common English names! Sorry, folks, I've never heard them referred to as anything but Peripatus here in NZ. Velvet worms? That's about as intuitive as a brick!
Reply | Report Abuse | Link to thisAnd the reason that the age and physical condition of the proposer is relevant would bewhat?
Reply | Report Abuse | Link to thisThe hypothesis that the metamorphosis from caterpillar to butterfly result from that the mate of two different animals maybe only be kidding, but I think it must make the world return to the heat discussion about this transitino.
Reply | Report Abuse | Link to thisI am not a scientist, but it seems plausible. Suppose that the DNA did not combine together as it normally would, taking bits of information from each supplier, but instead one species' DNA operated at the beginning of the life cycle, and the other species' DNA operated at the end of the life cycle. In both, the DNA combines, just in different ways.
Reply | Report Abuse | Link to thisWere there no error margins on the paper? Otherwise, I'm more dismayed by the reactions of the self-assured. So much for looking at every theory no matter how obtuse. Lucky for the NAS they have Lynn Margulis to see the big picture and provide proper scientific perspective.
Reply | Report Abuse | Link to thisAll ideas warrant testing. Not that I'd expect much to confirm this theory, but for scientists to proudly voice their preference that a dissenting view not be discussed at all... This is a large part of what we claim elevates science over stuck-in-the-past religious dogma. Test it, shoot it full of holes, lets see the data. Authority holds no weight.
Nature IS weird. If there's one thing we should know about it, it's that just because something happens one way, doesn't mean it's going to happen that way 100% of the time. 99.999% even, maybe, but not 100%, and when you consider how many species there have been, and how many individuals there have been, that's a lot of opportunity for weird. We know there are millions of biological accidents and freak occurrences, and every blue moon, one scrapes by and makes it. This would be highly weird, but then there are weirder things in nature yet too.
I'm glad to see this being discussed. The mechanism of metamorphosis is one of the more spectacular and weirder things in nature, regardless of explanation. More research is better research. If it motivates even twenty people to look into it further, and even one of them discovers something new about the process, then that is knowledge gained through the healthy exercise of competition and free exchange of ideas, as it should be.
"one for the socialists"? I'd ask you to explain yourself, but, it looks like you already did.
hotblack, I'm not sure what you mean by error margins. But: not all ideas are created equal and peer-review exists to screen for those with sufficiently argued merit to warrant publication. Which is an excessively fancy way of saying that one cannot simply say anything one wants without proof, and appeal to the Ideals of Science to get it published. That is not different between the scientific method, or any other method. Even in religion, one is expected to provide theological evidence from study of the relevant works. The only difference between science and religion is that the basic understanding of science is mutable. There is a common misconception that the glory of science is allowing all ideas to be discussed, regardless of merit. This is not true. In the scientific process, evidence is collected which leads to a conclusion. Ideas are not discussed, evidence is discussed, because ideas are inherently biased. Insofar as how this is presented here, there is no evidence except, "These look the same, they must be the same". As an example of what science is not,
Reply | Report Abuse | Link to this"Aristotle maintained that women have fewer teeth than men; although he was twice married, it never occurred to him to verify this statement by examining his wives' mouths." -Bertrand Russell
Aristotle's idea would not be publishable because no evidence has been provided. There is no discussion of the idea at all, because Greek philosophy was based on opinions, not experimentation. To be publishable, the author must establish the case. Otherwise we could say all sorts of wacky things.
However, the real impact of the theory is that it was published in PNAS, which questions whether Margulis subverted editorial standards in order to have this published. Margulis has not provided scientific perspective, since she believes she should have the final say over reviewers. That's not science, that's Infallibility.
Regardless of whether there is merit to the theory, the mere fact of publication in PNAS lends insta-credibility to the theory. Researchers unfamiliar with the subject must take it seriously, because there is too much science for everyone to be aware of everything. We must trust in review and expertise. This being the case, given that citation distortion can lead to theories being 'proven' without any evidence(1) even within a field, it is irresponsible for a journal of PNAS's reputation to publish material that has so little merit that a majority of reviewers rejected it.
(1) http://www.bmj.com/cgi/content/abstract/339/jul20_3/b2680
When I was a biology undergraduate, I wrote a paper about one of Dr. Margulis's "weird theories"- that chloroplasts and mitochondia had evolved from colonization of single-celled organisms by symbiotic bacteria, some of which could photosynthesize. It was quite controversial at the time, but I I believe it is now a generally accepted theory. That does NOT necessarily mean that there is good (or any??) data to support Dr. Williamson's hypothesis, but the article should at least have acknowleged Dr. Margulis's track record.
Reply | Report Abuse | Link to this"There's more garbage published in PNAS than any other journal..."
Reply | Report Abuse | Link to thisI heard a biochemistry graduate student say that in about 1968. That's partly bad but partly good.
I think an 87 year old scientist should be allowed to offer/suggest an off-the-wall hypothesis like this for later generations to keep in the back of their minds without asking him to bear some burden of proof.
Members of the National Academy of Science have earned the right to think outside the box now and then.
"There's more garbage published in PNAS than any other journal..."
Reply | Report Abuse | Link to thisI heard a biochemistry graduate student say that in about 1968.
I think an 87 year old scientist should be allowed to offer/suggest an off-the-wall hypothesis like this for later generations to keep in the back of their minds without asking him to bear some burden of proof.
Why did Scientific American think it was useful to describe Donald Williamson as "a wheelchair-bound 87-year-old zoologist"?
Reply | Report Abuse | Link to thisCan you be more specific about where Williamson's article is or will be published? The DOI in your link (10.1073/pnas.0908357106) either has not been created or is incorrect, and the article is not in "the current" (or any) "issue of Proceedings of the National Academy of Sciences."
Reply | Report Abuse | Link to thisIn addition, Lynn Margulis's name doesn't appear in the list of editors on the journal's masthead.
I'm not conversant enough with the field to comment on the validity of the theory but some of the objections seem to object to the statistical improbability of such a thing happening a few missing links for processes in the middle. That sure sounds familiar to me and we have a few accepted theories on the go like that.
Reply | Report Abuse | Link to thisRegardless of the validity or not, I am glad that stuff like this has a place to get published. Maybe this journal was coerced into publishing something it normally shouldn't have, but I think that this theory should be heard, considered, tested and rejected as may be before people get too upset. Heck, I can think of a dozen experiments already that might be interesting and informative.
There is little in the PNAS article that was not in his 2003 book
Reply | Report Abuse | Link to thisWilliamson DI (2003) The Origins of Larvae (Kluwer, Dordrecht, The Netherlands). You can find my review of that book at
BioScience 55(1):81-82. 2005
http://www.bioone.org/doi/full/10.1641/0006-3568%282005%29055%5B0081%3AIOVOAP%5D2.0.CO%3B2
Williamson has been publishing papers and books on his hypothesis of hybrid origins of larvae since the 1980s. His writings have been almost entirely hypothetical, repeated versions of the same idea over and over, but never with any empirical data. He once claimed to have "tested" his hypothesis experimentally by hybridizing between phyla and getting viable early embryos. Subsequent attempts to repeat these experiments in U.S. and British laboratories failed (this work was published). It amazes me that any editor would allow this long-discredited idea to again be published in a reputable journal, especially given that the paper has nothing new to say and has no experimental underpinning (despite Williamson working on the idea for 25 years). Margulis seems to be unaware of this background, and she and PNAS have seriously undermined their credibility with this blatant manipulation of the peer review process.
Reply | Report Abuse | Link to thisOkay, so there's no evidence to support Donald Williamson's hypothesis, but why is it possibly relevant that he uses a wheelchair? "... Williamson, a wheelchair-bound 87-year-old zoologist" is a slur, and perpetuates the notion that people with physical disabilities are somehow less worthy of being taken seriously than non-disabled people.
Reply | Report Abuse | Link to thisI would tend to opt for the opinion of the man who thought the paper to be better suited to the National Enquirer !!! Too many UN-answered questions to let a simplistic answer slide by unchallenged !!!
Reply | Report Abuse | Link to thisI think the question should be asked of Brendan Borrell why he did not clarify what Professor Margulis actually meant when she said something about "6 or &" and "2 or 3". Was it the allure of a controversy a la National Enquirer that made this "quote" so irresitable? Why is Donald Williamson who spent most of his career studying the hybridization of marine larvae at the Port Erin Marine Station on the Isle of Man referred to as a retired zoologist? It is true, but misleading when it comes to his expertise. It is sadly not amazing that so many supposed scientists blog their decidedly uniformed opinions or opinions based on one article in the Scientific Inquirer.
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