Darwin as Ichthyologist: Lessons for Our Future
Early studies of fish exhibit hallmarks of future theory

By Daniel Pauly

The image conjured by the name Charles Darwin is usually that of an old man with a long beard who spent his life developing and refining his world-shaking theoretical insights on evolution. But before he was 'Darwin,' this son of a wealthy country doctor was a young man with a passion for field biology, both terrestrial and aquatic.  As an 18-year-old student in Edinburgh, Scotland, he penned an excellent account of the lumpfish, Cyclopterus lumpus.

As a fresh graduate of Cambridge University, this hands-on experience was the ideal preparation for the fieldwork that awaited him.  He became the unofficial naturalist on the H.M.S. Beagle when he accepted an invitation by Captain Robert Fitzroy in late 1831.    Darwin put his observation skills to wonderful use during the nearly 5-year voyage of the Beagle. This is well illustrated by his collection of fish, which interested him far more than his later work would suggest.

Darwin was aware that the best fish collections in the world, particularly those from the tropical Indo-Pacific region, were held by French ichthyologists (scientists who study fish).  His letters indicate he planned to collect fish from areas of southern South America that had not been well characterized. As soon as he began his field sampling on Cape Verde and in Brazil, Darwin began to observe, hypothesize and perform simple manipulations.  Characteristic of his seminal work, these strong fundamentals would later serve him well when questioning far-flung experts and undertaking more sophisticated experiments.

In Brazil he sampled Chilomycterus antennatus, a bridled burrfish which is a 'globefish' that can pump itself full of air.  He wisely packed his specimens with others in a barrel full of "spirit of wine" to be sent back for later description by an expert taxonomist (as most field naturalists of the time did).  He also recorded its live colors according to the paint samples in his field copy of Patrick Syme's booklet on "Werner's Nomenclature of Colours," and reported on its behavior, which he attempted to link with its anatomy.  Darwin noted the mechanism that enables this fish to inflate itself, and suggested that it may function to help blow water toward predators as one of its "several means of defense."  It turns out this is not the case.  Burrfish, like many other fish, 'blow' the worms and other small animals they feed on out of their sandy hiding places.  The idea of relating behavior to anatomy was still new at the time, but Darwin's famous thought process was already starting to define itself.

Darwin also suggested—erroneously—that parrotfish produced the white cliffs of Dover.  Although incorrect, these hypotheses illustrate that young Darwin had already absorbed the main message of Lyell's Principle of Geology, which he read on the Beagle: Small causes, acting over large areas and through deep time, can move mountains.  This theme was a key element of natural selection, which Darwin published in 1859. Darwin's last book on the subterranean work of earthworms, published in 1871, reconnected with the basic theme underlying his parrotfish work 35 years earlier: Billions of earthworm bites over millions of years created and maintain the soils that much of terrestrial life, including our own, depend on. The greatness of Darwin is that he could see, in all his works, how little things acting over immense expanses of space and time, become Earth-shaping forces. We ignore this simple principle—which is also behind global warming—at our own peril.

Daniel Pauly is a French-born professor of ichthyology at the Fisheries Centre at the University of British Columbia, Vancouver, Canada, where he was the director for five years from November 2003 to October 2008.  He is the author or co-author of more than 500 scientific articles, book chapters and shorter contributions.  He is the author, editor or co-editor of nearly 30 books and reports.  He teaches courses and supervises students in four languages on five continents.  In 2004, he published "Darwin's Fishes: An Encyclopedia of Ichthyology, Ecology and Evolution," Cambridge University Press.

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Rethinking the Birdtree of Life:
Modern genetic studies reveal Darwin's finches are not finches at all
By Sushma Reddy and Shannon Hackett

Charles Darwin referred to birds often when making his case in "On the Origin of Species."  Well before Darwin's time and beyond, birds were among the most loved and well-studied organisms.  Studies of these conspicuous and often beautiful animals have shaped biological thought—from natural history to behavior, ecology, reproduction, speciation, vocalization, cognition, evolution and more.  Given all this attention, it is surprising that avian evolutionary relationships—the bird tree of life—have remained so unresolved.

The high-species diversity of birds, compared to some other vertebrate groups, has long inspired speculation about their origin.  Since Darwin's time, theories have been put forward to explain this diversity, but research demonstrates there is no simple explanation.  For instance, there are few common features shared by major groups of birds to suggest their relationships—for example, parrots look like other parrots, yet have little in common, morphologically, with other birds; the same is true for owls or pelicans and so forth.  Researchers used what little evidence was available from observation of morphology, behavior and ecology, to assess how birds were interrelated.  More recently, genetic data began to piece together parts of the puzzle, but results from early studies were varied, often inconclusive, and even inconsistent.

Scientists now believe the problem stems from the shape of the bird evolutionary tree.  From fossil and genetic evidence, researchers think modern groups of birds diverged into their different forms within a few million years of one another, about 65-100 million years ago.  This makes the matter of deciphering the evolutionary history of birds a complex problem requiring far more data than has ever been collected to address the problem.

For more than five years, we have been part of a collaborative project to study this big mystery regarding birds.  We set out to study the deep evolutionary history of birds using massive amounts of DNA from all the major groups of birds.  Our study benefited from technological advances that allowed us to collect large amounts of sequence data, as well as data from recent genome projects such as those for human and chicken, which have greatly contributed to our knowledge of genomes.  Using 19 different genes, or more than 32,000 DNA base-pairs for each of the 169 bird species, we deciphered a robust "family tree" of birds.  Our study revealed several unexpected yet strongly supported relationships, and showed that much of conventional wisdom on the evolution of birds is wrong.

One important lesson from this study is that appearances can be misleading.  Many different looking bird groups are actually closely related.  Some of these unlikely "cousins" include parrots and songbirds, flamingos and grebes, and hummingbirds and nightjars.  And, many of the groups that do look and act similar turn out not to be closely related.  For example, birds of prey or raptors, such as falcons and hawks, independently evolved similar lifestyles.  Likewise, owls and nightjars, both nocturnal, cryptically colored groups, are unrelated.  Interpretation of many adaptations to different lifestyles, environments and behaviors can now be assessed with this new historical perspective.

Our study, along with other recent genetic studies, demonstrates that much of bird classification is wrong.  Many of the traditional orders, families, genera and even species are not natural groups, indicating that many of the traditional features used to unite these groups do not reflect the evolutionary history of the birds, as previously assumed.

Another example of complicated bird evolution, particularly relevant as we celebrate Darwin and his life and accomplishments, comes from one of the most studied and influential group of birds—Darwin's finches of the Galapagos, which have long been considered a classic case of adaptive radiation.  Some of the most elegant and detailed studies demonstrating evolution by means of natural selection have been done on these finches.  However, genetic studies suggest we have a lot to learn, even about this famous group of birds.  Despite their morphological diversity, birds classified in different species based on distinct bill size have identical or nearly identical DNA.  In addition, the use of DNA sequence data to find the finches' place in the avian tree of life shows that Darwin's finches are not finches at all, but instead, belong to the family of tanagers.  New data and approaches can reinterpret even the most familiar of textbook examples.

As we continue to explore and piece together the puzzle of the bird tree of life, we will undoubtedly discover and reinterpret other fascinating facets of avian evolution.  Birds exhibit incredible diversity and using this "family tree," we can begin to grasp how these varieties originated.  By better understanding how birds evolved, we also better understand the features that have fascinated so many scientists and amateurs for centuries.

Sushma Reddy is currently a postdoctoral fellow at the Field Museum of Natural History in Chicago, Ill., working on the Early Bird project, part of the National Science Foundation-supported Assembling the Tree of Life (AToL), program.  She became an assistant professor of biology at Loyola University Chicago in the fall of 2009.  Her research covers topics in evolution, biogeography and genetics, primarily using birds but also other vertebrates. Shannon Hackett is the associate curator and head of the Bird Division at the Field Museum of Natural History in Chicago, Ill., and co-chair of the Committee on Evolutionary Biology at the University of Chicago.  She is also a fellow of the American Ornithologist' Union.  She is researching the evolution of birds as part of the Early Bird project, part of the National Science Foundation-supported Assembling the Tree of Life (AToL), program.

Please see the Resources section for the Bibliography/Additional Reading list for this essay.

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What If Darwin Hadn't Written "On the Origin of Species?"
Darwin's methodology may equal his ideas in scientific importance
By Marsha Richmond

Evolution is so interwoven into the fabric of modern life that it is almost impossible to imagine the world without it.  This was not the case for Charles Darwin (1809-1882).  European cultures, influenced by Aristotle as well as the Bible, viewed the world as stable and orderly, with living organisms linked in a great "chain of being."  British natural theologian William Paley explained adaptation by teaching that each creature was designed for a purpose by the Creator.  While a few natural philosophers, most notably Jean-Baptiste Lamarck and Darwin's grandfather Erasmus Darwin, speculated about organisms changing over time, such views were considered unorthodox, if not heretical.

Darwin began to doubt the "fixity of species" soon after his five year voyage on the HMS Beagle (1831-1836).  As he noted in the opening passage of "On the Origin of Species":

When on board H.M.S. "Beagle," as naturalist, I was much struck with certain facts in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to me to throw some light on the origin of species—that mystery of mysteries, as it has been called by one of our greatest philosophers. (Origin, p. 1)

In 1838, Darwin began to sketch out his idea of "natural selection."  For two decades he collected a myriad of facts bearing on his theory.  Finally, he began writing his "big species book" when in June 1858, he received a letter from Alfred Russel Wallace, a British naturalist collecting specimens in the Malay archipelago, enclosing a manuscript for Darwin to read.  He was thunderstruck by the manuscript's similarities to his own ideas.  This forced Darwin into action, and, with the help of his friends Charles Lyell and Joseph Dalton Hooker, his 1844 essay was published along with Wallace's paper in the Journal of the Proceedings of the Linnean Society of London in August 1858.  Darwin then rushed an "abstract" of his views into print: On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life appeared on 24 November 1859.

Darwin, then, was not the first to conceive of evolution, nor the only one to develop a theory of natural selection.  This is not to say, however, that had he not published "On the Origin of Species"that natural science would have fared the same.  Darwin's book contributed more to posterity than simply the idea of evolution or the theory of natural selection.

Darwin's methodology revolutionized the life sciences, setting the stage for major advances in twentieth-century biology.  Prior to Origin, natural historians primarily engaged in describing and naming organisms, along with studying their anatomy and physiology.  To establish his claim that organisms evolved over time by means of natural selection, Darwin had to lay out a vast array of empirical evidence drawn from many different areas of natural history and then formulate "one long argument" to explain these observations (Origin, p. 459).  Darwin relied on the use of analogy and inductive reasoning to support his theory of natural selection. Invoking the philosopher William Whewell's notion of "consilience of inductions," Darwin argued that any theory that was able to explain so many different classes of facts was not likely to be false.  After 1859, Darwin's hypothesis-driven research program, now called the "hypothetico-deductive" method, in addition to his particular theory of evolution, became the foundation for future work in biology.

Thus, Darwin's legacy to posterity lies as much in revolutionizing the methodology of the life sciences as in offering particular views about evolution.  Wallace and others likely would have introduced evolutionary views describing lawful change in organic life.  Yet it is hard to envision any work that would have been able to match the persuasive power of "On the Origin of Species," not simply in explaining the diversity of life but also in instructing naturalists about how to investigate complex relationships. Indeed, "On the Origin of Species" continues to serve as a striking exemplar of how to do good science.  Historians generally shy away from engaging in "what if" stories, but most would agree that had "On the Origin of Species" not been published, we would still believe in evolution, but the development of modern biology would have unfolded much differently, and with less striking success.

Marsha Richmond is an associate professor of history at Wayne State University in Detroit, Mich. A historian of late nineteenth- and early twentieth-century biology, her research focuses on Darwin's views of heredity, the history of evolution theory, the rise of modern genetics, and the entry of women into biology.  She is a U.S. Advisor to the Correspondence of Charles Darwin Project, based in Cambridge, England. The National Science Foundation supports her work on Women in the Early History of Genetics.ence Red in Tooth and Claw. 2nd ed. Chicago: University of Chicago Press.

Please see the Resources section for the Bibliography/Additional Reading list for this essay.

The Mythology of Natural Selection
Darwin's ideas were crafted and refined within communities in London, not in isolation on the Galapagos
By Jim Secord

Where did Charles Darwin become convinced of the truth of evolution? Certainly not in the Galapagos Islands, with its extraordinary animals and plants, but rather in the smoky, noisy world of early Victorian London.

The story goes that Darwin was so struck by the unique fauna of the Galapagos during his five year voyage aboard the HMS Beagle that he immediately abandoned his belief in the stability of species. More than that, it is often claimed that his observations of finches, the beaks of which vary from island to island, immediately led him to believe in natural selection. But these accounts of instant conversion are myths. During the long, boring months of Beagle's return to England, Darwin's doubts about species began to crystallize.

It was only after moving to London in 1837, that he became a convinced evolutionist. The significance of Darwin's finds started to take shape when experts such as the bird man, John Gould, began to identify his Galapagos specimens. ;The different varieties of tortoises and mockingbirds provided powerful evidence of the relations between the Galapagos fauna and that of nearby South America. In geographical space, as in geologic time, closely allied species emerged successively and in order, just as they did in the fossil record. These relations, which impressed Darwin throughout the voyage, suggested that species were not specially created.

As for the Galapagos finches, during his brief stay, Darwin failed to notice the significance of the variations of birds found on different islands. In a brilliant piece of detective work, historian Frank Sulloway examined Darwin's specimens now held in the Natural History Museum in London. It turns out that Darwin had been skeptical of local reports that the finches varied, so back in London his labels had to be corrected as much as possible using the collections of his shipmates. So despite popular claims, evidence suggests the Galapagos finches were not the reason for Darwin developing his theory of natural selection.

Instead, the inspiration came when Darwin combined insights from his post-voyage inquiries into breeding-related reproduction and generation, with an understanding of economics-based population increase. At that time, London was a hotbed of discussion about new theories in the sciences, so it is entirely appropriate that the central theory of modern biology was elaborated in a dingy bachelor's flat in a crowded city—the largest the world had ever known.

To imagine that natural selection emerged fully when the Beagle landed on the Galapagos not only minimizes the challenges Darwin faced, but also fails to recognize that even the greatest innovations in science depend upon others. Today the Galapagos are a marvellous laboratory for understanding evolution, but only because Darwin made them so.

Jim Secord is director of the Darwin Correspondence Project, professor of history and philosophy of science at the University of Cambridge and a fellow of Christ's College. He recently edited Darwin's Evolutionary Writings for Oxford University Press, including the full text of his autobiography.

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