The Mystery of Metamorphosis: A Scientific Detective Story

  • By Frank Ryan
  • Chelsea Green Publishing
  • 320 pp.

This look at a fascinating subject takes a wrong path.

My organization advocates for federal funding of scientific research, and we keep a book called They All Laughed by Ira Flatow around to remind us that important and valuable science sometimes sounds useless, silly, even downright crazy. Like policymakers or the general public, members of the scientific community are not immune from dismissing good ideas when they sound crazy or conflict with existing theories. The ubiquity of Thomas Kuhn’s The Structure of Scientific Revolutions on the shelves of graduate students everywhere is testimony that paradigm-shifting scientific theories are likely to encounter significant resistance, and, at the same time, that many scientists desire to be part of such a revolution.

Yet the scientific community’s natural skepticism is reasonable. Many ideas sound crazy because they are; the difference between crazy and revolutionary comes down to testable predictions and supporting evidence. The failure of Frank Ryan’s book The Mystery of Metamorphosis, which tackles a fascinating subject, is that its central thesis is framed around a hypothesis that has already been roundly rejected by the scientific community — not that a layperson would know it by reading the book, which falsely equates romantic iconoclasm with scientific validity.

The transformation of caterpillars to butterflies and tadpoles to frogs are the best-known examples, but metamorphosis occurs in many groups of animals, especially marine invertebrates. This book focuses on two main threads of metamorphosis research, which Ryan connects in only the most tenuous fashion. The first is physiological studies, many done earlier in the 20th century, elucidating the critical role of hormones in insect metamorphosis. Though the litany of experiments is both grisly (much severing of insect heads and transplantation of brains) and occasionally tedious, there’s little to object to. The problems occur with the book’s second thread, the evolution of metamorphosis.

In advocating a prominent role for hybridization in the evolution of metamorphosis, Ryan champions the views of Donald Williamson, a retired British zoologist who hypothesizes that distinct larval and adult forms arose through chance interbreeding between groups of distantly related organisms. The hybrids express the forms of the parental organisms sequentially, with an intervening metamorphic stage as the result. Understanding why this idea is so controversial requires consideration of some core concepts in evolutionary biology.

Species — such as humans, shrimp or starfish — are, as a general rule, reproductively isolated from one another. That means they cannot produce viable interspecies offspring. As a result, species have distinct evolutionary trajectories. Evolutionary biologists accept that hybridization between very closely related species sometimes occurs, but the more distantly related species are, the less likely such interbreeding becomes.

Williamson essentially postulates that interbreeding occurs between not just different species but different phyla; for example, between ascidians (sea squirts) and echinoderms (sea urchins). He postulates that this has happened repeatedly between different groups of widely divergent organisms. Moreover, he postulates that the hybrids look like one parental species as larvae and like the other as adults, rather than simply exhibiting a mix of characteristics, as most hybrids do. Not only is this hypothesis not supported by evidence, but plenty of evidence, including powerful molecular evidence, directly contradicts it.

Ryan provides a blow-by-blow account of Williamson’s struggles to get his views published in peer-reviewed journals, but it is hard to be sympathetic when Williamson continually fails to provide any new evidence. Most tellingly, while Ryan discusses Williamson’s attempt to publish in the prestigious Proceedings of the National Academy of Sciences (PNAS) in the late 1980s, he omits to mention Williamson’s infamous interaction with that journal two decades later.

It turns out that Williamson did publish a paper in PNAS in 2009. Ryan cites this paper without comment in the book’s epilogue, and does not mention that the paper stirred up significant controversy in the scientific community, ultimately contributing to a change in PNAS peer-review policies. Nor does he mention that the paper was thoroughly rebutted by a later submission to the same journal. Not discussing this is unconscionable, and solidifies my impression of Ryan as an unreliable narrator.

It is not clear whether this book is primarily geared to scientists or to the general public. The bibliography, even including sources in chapter references, is too thin to be of much use to researchers, but the prose is often dense enough to be daunting for anyone not versed in invertebrate taxonomy and anatomy.

An even bigger problem is that small sketches on the title page of each chapter are the book’s only illustrations. Most people are not familiar with the adults, much less the larvae, of groups like echinoderms, onychophorans or ascidians. The book would have benefitted from clear diagrams showing things like the evolutionary relationships of these groups and the symmetries and developmental patterns discussed. It also should have included color photos of larval and adult forms of some of these organisms, as well as of metamorphosis in action.

A book that unites physiological studies, the fossil record and new findings in evolutionary developmental biology — synthesizing what we know and illuminating what we do not  — would be a fascinating and useful addition to our understanding of the mystery of metamorphosis. This, however, is not that book.

Contrary to the book’s message, Williamson’s ideas have not been stifled by the scientific community; he has published numerous books and papers, including the PNAS paper, elucidating his theory over the last 20 years. So where is the army of hungry graduate students and postdocs throwing their Kuhn volumes back on the shelf and leaping to the lab bench in their haste to make a scientific revolution, and their own careers, with Williamson’s ideas? Their absence says much; it certainly says more about the validity of these ideas than Ryan’s book.

Josh Trapani, the Independent’s senior managing editor, has a doctorate in paleontology and spent two years as a postdoctoral researcher in ecology and evolutionary biology. Now he works at the interface of science and policy.

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