Darwinizing Metamorphosis with Magic - Evolution News & Views

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Darwinizing Metamorphosis with Magic

Pity the party that tries to Darwinize metamorphosis: to give an evolutionary explanation for the transformation from caterpillar to butterfly that resembles death and resurrection. One bold evolutionist has given it a try, but is his explanation an appeal to magic?

Thumbnail image for metamorphosis-bluray.jpgIn the documentary Metamorphosis from Illustra Media, biologist Richard Stringer explains why he was attracted to the study of butterflies. "That's biology; it's also magic." Of course he intended the reference to magic as a metaphor, because he proceeded to investigate metamorphosis scientifically, examining the process in detail with MRI. Frank Ryan, however, writing for New Scientist, is weak on details and big on veritable magic, speaking of how metamorphosis arose or emerged with little more causation than casual sex and hormones.

As noted earlier here at ENV, many organisms exhibit metamorphosis. Butterflies and moths put on the most spectacular show, but other flying insects, echinoderms, amphibians, fungi, mosses, and 15 phyla of marine organisms have their versions of shape-shifting "magic" acts. Even a human embryo in the blastula stage is a far cry from what it will look like at birth, but essentially, metamorphosis refers to the transformation from one body plan to another. Ryan focused his attention on marine metamorphic processes rather than try to take on the Darwin-eating butterflies all at once. Did he succeed? Only if one allows virtual miracles and some pretty cranky science.

Frank Ryan should know; he wrote a book called Metamorphosis: Unmasking the Mystery of How Life Transforms. To see what Ryan proposes, the reader of his abbreviated article must sweep away dust bunnies of irrelevant verbiage (some of it the stuff of an interesting historical anecdote about early Darwinian ideas about metamorphosis, now debunked and defunct). In a sidebar he attributes butterfly metamorphosis to hormones, particularly ecdysone. What a molecule; it must be the world's greatest magician. Watch this trick: "Then, when all the larva-to-larva molts have occurred, the breaks [sic] are lifted and ecdysone alone orchestrates the spectacular final transformation to the adult." Stop clapping and sit down.

His centerpiece is a tribute to Donald Williamson, a planktonologist from the University of Liverpool, who worked in the 1950s on a so-called "larval transfer" hypothesis -- an idea so radical it "provoked frank disbelief among many biologists" (e.g., see the uncharitable remarks posted by Scientific American in 2009). If a better theory existed, the author of a book on metamorphosis would certainly have focused on it instead. Williamson's "controversial theory" proposed that "widely separated evolutionary lineages had occasionally come together to form hybrid species." You may now tell your favorite joke from the "what do you get when you cross a gorilla with a banana?" genre.

Ryan's magician marched right past the disbelief of his peers. "Undaunted, Williamson set out to confirm it in an extraordinary series of experiments involving improbable sexual crosses between animals from different marine invertebrate phyla." Unfortunately for science, Williamson, "working alone," claimed amazing crosses between unrelated larvae that others could not replicate.

But wait, there's more! Ryan gives his hero an even greater labor of Hercules -- explaining the Cambrian explosion! "No convincing explanation has ever been proposed for such major and rapid evolutionary change," Ryan admits. But that doesn't stop him from giving Williamson a chance at a knockout blow: "In 2006 Williamson extended his ideas to propose that hybridization, with its potential for very rapid evolutionary change, might help to explain the origins of the animal kingdom itself," he said. Now that's biology; it's also magic!

If this were a circus act, it would be time to fold the tent. "While many biologists still dismiss Williamson's ideas as overly speculative, research published last year indicates that they may not be as wild as some have suggested." Readers are comforted to know that the ideas are wild, but not as wild as you might think. This softens the blow a little as Ryan tracks a red herring about phylogenetic trees (you know, those mental constructs built on Darwinian reasoning). But then, Ryan ends with a masterful spin on his magic show masquerading as an explanation for metamorphosis. Ready?

"It is fascinating to think that the same processes might underpin metamorphosis in marine invertebrates and be an overlooked source of creativity in evolution." Fascinating to think, yes. Source of creativity? Hmm, not so sure about that. "Of course, Williamson's theory remains on the fringes," he admits. (Stop right there and imagine a Darwin skeptic announcing something like that at the AAAS.) No matter; Darwinians get applause just for effort expended: "but whether it is eventually accepted or refuted, he has done biology a service in highlighting the importance of metamorphosis as a clue to some of the deepest mysteries in biology."

To Darwinians, it's not whether you win or lose, but how you fool the audience.