The big Darwin year of 2009 made me realize just how many ways there are to approach Darwin's life, his ideas, and his theory. I've read only a smattering of the books that have appeared on these subjects in the past few years, but even they range widely. Some authors, like David Quammen (2006), look at Darwin's life, while others, such as Jerry Coyne (2009), examine the theory. I consider both these books above average in their respective niches. Quammen's is succinct and gives the story some drama by focusing on Darwin's reluctance to publish about his theory. Coyne does just about the best job I've encountered of laying out the argument for evolution both clearly and with a broad range of evidence.
Then there are books that focus more narrowly on particular aspects of the man or his work. Here, as with the theory itself, there are endless possible avenues, and it seems that authors have trod a great many of them. I happen to be interested in visual representations in science, so I've read Jonathan Smith's Darwin and Victorian Visual Culture (2006), which is a broad review of Darwin's use of images in his books. Also, there's Julia Voss's recent Darwin's Pictures (2010), which is more focused, dealing with four images in depth. Even more specific is Constance Clark's God – or Gorilla: Images of Evolution in the Jazz Age (2008), which is less about Darwin's theory and more about how it was viewed in American popular culture. And these books are just on the subject of images.
Sticking to more theory-related topics, there's Sean Carroll's Endless Forms Most Beautiful (2005) on the relationship between evolution and development – or evo-devo, as it is more concisely called. Marc Kirschner and John Gerhart (2005) write about why evolution is a plausible explanation for the diversity of life on earth, and David Mindell (2006) looks at evolutionary change occurring today. This list could go on and on, so I'll stop, but only after mentioning two books with great titles. First there's Bozo Sapiens by the husband and wife team of Michael and Ellen Kaplan (2009). It provides an evolutionary explanation for why humans make mistakes and is an example of the use of a clever way into evolutionary theory. The other title champion is Neil Shubin's Your Inner Fish (2008), employing the earliest vertebrate as a path into exploring the history of life on earth. It's a well-written and understandable explanation of evolution and another example of how focusing on one area of evolution can help to tame the information available on the subject.
This brings me to a book on evolution that I've just read, Dennis McCarthy's Here Be Dragons (2009). It's the story of how studying the geographic distributions of plants and animals around the world fueled the development of evolutionary theory. Its title comes from an old expression found on an early 16th-century map implying that the area marked with this phrase – in Southeast Asia – would be a dangerous place to visit. In other words, different parts of the world are home to different creatures, some of which may be better left alone. McCarthy begins with the observation that it seems more than coincidence that so many of the major figures in the history of biology were interested in the subject of biogeography. He names Carl Linnaeus, Charles Darwin, and Alfred Russel Wallace, along with two present-day biologists, Edward O. Wilson and Jared Diamond. He adds Alfred Wegener, not a biologist but a geologist, who is responsible for the idea of continental drift, which draws heavily on biogeography for its substantiation. I would add to McCarthy's list, but I'll get to that later.
I bought Here Be Dragons for two reasons. First, my Scientific Inquiry course this semester is part of a learning community along with a Discover New York course, and we are using the subject of maps as a unifying theme. Biogeography is obviously relevant, and in addition, I had read an enthusiastic review of the book by Devorah Bennu (2010). She ends with the statement: “The book delivers on its promise that we will never look at the world the same way again” (p. 1637). Well, I had to get a book that memorable.
After I had finished reading Here Be Dragons, I went back to the review, and found that I wasn't quite ready to agree with that last sentence. Maybe I came to the book as too much of a biologist. Not that I'm an expert on biogeography, but it's not news to me that Darwin's trip to the Galápagos Islands was pivotal to the development of his theory, that island biogeography holds clues to evolutionary change, and that plate tectonics, which McCarthy covers in some detail, explains the movement of continents. However, as often happens to me, I eventually revised my first impressions. The more I thought about the book, the more I realized that while it didn't change the way I looked at the world, it did alter the way I thought about evolution. I became much more aware of evolution as a matter of geography. It suddenly seemed terribly obvious that geography provides a powerful way to view evolution.
It was this simple insight that got me thinking about all the books that deal with evolution, and that explore various aspects of it. I was amazed anew at the richness of the theory – hardly a revolutionary thought, but one that's good for a biologist to ponder every so often. Of course, biogeography is a particularly rich topic because, to put it simplistically, natural selection is driven by environmental change. The environment does the selecting, and geography is the sum total of that environment, so it's not surprising that it took someone who had experienced a lot of geography to come up with the theory of evolution. Darwin, after all, went around the world before the idea dawned on him, and Alfred Russel Wallace, the co-discoverer of natural selection, had spent a few years in South America and then headed for New Guinea, where the concept came to him.
The Galápagos & Beyond
McCarthy begins, not surprisingly, with the Galápagos and Darwin's experiences there – and afterward. The islands had a delayed effect on Darwin. While visiting them, he was impressed by the differences in the traits of birds found on the islands, but at that point he really didn't know the questions to ask. It was only when he returned to England that Darwin began to think more seriously about the relationship between place and species characteristics. One prod came from the ornithologist John Gould, who examined the bird skins Darwin had collected and asked questions about them, such as which Galápagos birds came from which islands. Darwin's earlier experiences in South America, examining fossils and noting the similarity, but not identity, between the fossil organisms and present-day species, also triggered more thoughts on species change and its relationship to geography. This points up the fact that the effects of travel aren't all felt in the first few weeks after returning home. Yes, that's when people tend to talk about their trips, but later events may make them think about their experiences again and again – and in new ways.
Among the other topics McCarthy covers is how the sometime link between North and South America explains that fossil record as well as the present distribution of animals. He also discusses why islands are such catalysts for evolution. Obviously, they were important to both Darwin and Wallace, but they continue to be significant to today's evolutionary biologists, as Jonathan Losos and Robert Ricklefs (2009) discuss in a review article written to commemorate Darwin's birth. They argue that much of the research on island evolutionary diversification today is a direct result of Darwin's insights. He established the basic principles that are still the source of rich research questions today. And though he was born on an island, it took travel to some distant ones to provide the fuel for his insights.
McCarthy also covers New Guinea and Wallace, whose desire to explore was sparked by his reading of Darwin's voyage journal. McCarthy describes how Wallace's investigation of the flora and fauna on various islands in the area prompted him to develop the hypothesis that there was a significant difference between organisms over a narrow geographic range, and to mark a line on the map denoting the boundary between two very distinct biogeographic regions. This became known as Wallace's Line, and though it has been slightly redrawn, it remains a potent biogeographic observation. As with many interesting observations in biology, the explanation for this curious distinction didn't become clear for a long time – almost a century. The geological theory of plate tectonics made plausible the suggestion that regions that are near each other today had once been distant and, therefore, home to different evolutionary histories.
But I'm getting ahead of McCarthy's story; he does arrive at plate tectonics, but via Wegener's idea of continental drift and the posited supercontinent of Pangaea, which plate tectonics made plausible. Once this explanation was developed, it was much easier to find supporting evidence for it because geologists then had a better idea of what they were looking for. McCarthy also presents a number of other case studies in biogeography, such as the coincidence in the shape of the east coast of South America and the west coast of Africa, which makes them look like they would fit together. What makes this particularly remarkable is that the flora and fauna of these regions are also similar, even though they are now thousands of miles apart.
Another intriguing biogeographic issue is one I remember reading about years ago in a biography of Asa Gray, an American botanist and frequent correspondent with Darwin but not a big traveler, though he did get to England once to meet Darwin (Dupree, 1959). Gray was fascinated by the fact that there were notable similarities between the flora of the east coast of the United States and that of Japan. Japan! Now that made me sit up and take notice. I may have come across this information earlier, but it hadn't stuck with me as it did after reading this passage. This is a question that still intrigues biogeographers, and their explanation is an outgrowth of the ideas that Gray posited in the 19th century (Wen, 1999). He explained the parallel as due to similar climate and geography as glaciers receded after ice ages of the tertiary period; this would lead to selection for similar characteristics.
To explain all these biogeographic observations, maps are essential. There are even short videos available on the Web that show how the land masses came together and then separated. I find these useful, especially when I stop them at various points to get a better sense of where different land masses abutted each other. Pangaea is fun, and maybe that's one of the reasons I found McCarthy's book so enjoyable. I didn't learn a great deal new from it, but I developed an increased appreciation for the significance of geography to evolutionary theory.
Obviously, there were inklings of these links long before Humboldt and Wallace, who is considered the father of biogeography, described them. A number of maps created during the age of discovery hint at them. The zoologist Wilma George (1969) has written on the animals depicted in old maps. In some cases, the representations are of beasts that we now know don't (and didn't) exist, but there are also realistic images of the rhinoceros, elephant, and lion on maps dating to the 16th century. And these beasts are situated where they are native species: Africa for all of them, and Asia as well for the first two. Even mapmakers of this time knew that place and creature were tied together.
A great resource on the subject of organisms and maps is The Natures of Maps, written by two geographers, Denis Wood and John Fels (2008). The title may seem a bit odd, but it accurately describes the subject of the book: the way in which nature is depicted on maps and how this reflects on the basic function of maps. Some of the maps the authors analyze appear to be, essentially, updated versions of those produced in the 16th century, with animals native to particular locales pictured on a map of that region. We so take this convention for granted that we don't think twice about it, and consequently accept the information displayed. However, Wood and Fels go deeper and also note what information is not presented. For example, in a National Geographic map of Australia, there are a large number of animals pictured, but mammals and birds predominate, even though there are many more species of reptiles, amphibians, and fish, to say nothing of invertebrates. Although the map is titled “Land of Living Fossils,” there isn't much here about plants either, except for a eucalyptus tree in which some koalas perch.
The authors argue that the map says as much about the map's viewers as it does about the biology of Australia: we are interested in large and showy animals. In any map, choices have to be made on what to present and what to eliminate, and those choices are often driven by factors other than scientific accuracy. The “Living Fossils” map and some of the others in the book, including other National Geographic maps, “The World of Flowers” and “Bird Migration in the Americas,” are wonderful studies in just such selection. Meanwhile, my learning-community colleague is dealing with the New York City subway map, where routes are presented accurately but aboveground landmarks are cited only sparsely. So students are getting great lessons in visual literacy in both classes.
Maps on the Web
I also plan to use one of my favorite Web “toys” in my course, WorldMapper (http://www.worldmapper.org), which has a variety of different maps drawn to specific statistical scales. For example, a map of native plant species shows a disproportionately large South America, Africa, and Southeast Asia and a squished Canada and Russia. On the other hand, a map of biocapacity displays a much larger South America as opposed to Africa. The only problem with this site is that it's so fascinating that you will have a difficult time tearing yourself away from it. The same is true of Google Earth (http://earth.google.com). Another site that's interesting to visit is the Natural History Museum of Barcelona Database (http://mapa.bioexplora.cat/). It contains 150 years of biological data collected around the world by the museum. The homepage displays a map indicating where collections have been made, and, not surprisingly, the greatest number of records is from Europe, and especially Spain. However, it's not just the data but the way they are displayed that's fascinating. It seems to be a format that could be emulated by other sites, since it cleverly combines information on organisms with geographic data.
And before I leave the subject of maps on the Web, I want to mention one more I've discovered; it's a map of the southern tip of South America that was hand colored by none other than Charles Darwin (http://www.lib.cam.ac.uk/exhibitions/Darwin/bigpics/Geological_map.jpg). It's a printed map with the various political areas clearly marked. What Darwin added was color as well as a hand-written legend in the lower left-hand corner. It presents a key to the colors; for example, gray denotes “basaltic lava,” tan is “clay-slate,” and rose is “granite mica slate.” The map represents not only a place but a mind working to make sense of the geological history of the place and what it means in relation to the fossils Darwin found there. Obviously, this area was much more real to Darwin after he had spent time exploring it, and this is documented in his notations. It's also worth noting that Darwin spent more time there than he had expected, because the Beagle's first attempt to round Cape Horn was unsuccessful and so they had to remain several more months along the southeastern coast of South America (Browne, 1995).
From the work of Darwin and Wallace it would seem that world travel fuels the biological imagination, and the reason why is obvious: there are so many different organisms and different ecosystems. Staying at home means exposure to only a tiny slice of this diversity. This was the fate of John Henslow, Darwin's mentor and the person who recommended him for the Beagle voyage (Walters & Stow, 2001). Henslow had dreams of foreign voyages, but his involvement with family and church prevented him from traveling. Perhaps it was this disappointment that led him to encourage his student to explore. Henslow knew that reading books and looking at pictures can somewhat draw aside the curtain to this broader world, but there are no substitutes for on-site experience. When he was asked to suggest someone to travel with Captain FitzRoy on The Beagle, he urged Darwin to take advantage of this opportunity. Henslow also worked to overcome Darwin's father's objections, by urging a Darwin uncle to intercede for the young university graduate.
The importance of foreign travel to the development of evolutionary theory is one of the major points in yet another recent book on evolution, Darwin's Armada by Iain McCalman (2009). He begins with Darwin's journey and then covers the voyages of Wallace and of two of Darwin's closet friends and confidants, Joseph Dalton Hooker and Thomas Huxley. All four circumnavigated the globe. Like Darwin, Huxley had one big trip. He met his future wife while in Australia, and when he got back to England he set about securing a stable professional position so that he could have her join him. Hooker, on the other hand, made separate voyages to Antarctica, India, and the Middle East (Endersby, 2008), collecting information about plants and visually documenting the species he saw in beautiful drawings (incidentally, Hooker married Henslow's daughter, Frances Harriet Henslow). Wallace, too, made a couple of major trips. He first spent a few years exploring the Amazon region on a very difficult expedition with Henry Bates. They finally made it safely back to England, but many of the plants and other organisms they collected didn't. For Wallace, this wasn't a deterrent to further travel. He went on a collecting expedition to New Guinea, and that's where he thought about species change and sent the famous 1858 letter and article to Darwin outlining natural selection.
All four of these world travelers wrote about their experiences, and they had all been influenced by an earlier voyager, Alexander von Humboldt. Along with Aiméé Bonpland, Humboldt explored South America and went on to write volumes about his travels. These books are full of information and stirring descriptions of the beauty of nature. Like many of the naturalists of his day, Humboldt was interested not just in one part of the natural world but in many, including astronomy, geology, and biology. These last two came to be joined in biogeography, to which Humboldt made a large contribution. In part, his input was visual. He created a large, complex chart called “The Outline of Botanical Geography,” which you can see at (http://www.historyshots.com/Botanical/index.cfm. This is one of my favorite scientific visualizations. It's so rich that it's difficult to describe in words. I'll just say that it includes a map that is color-coded for various ecosystems and marked with symbols of different plant communities, such as grassland or forest. There is also a representation of mountains indicating the different types of vegetation found at different altitudes.
Through his words and images, Humboldt really did change the way those who came after him saw the distribution of plants, and so I would add him to McCarthy's list of major figures in biogeography. One of the things that seem obvious when reading McCarthy's book is the close relationship between geography and biology. But this is not necessarily obvious to those who stick close to home. Yes, the plants in British seashore areas are different from those of the Midlands, but in the 19th century many people never even ventured that far, let alone saw deserts or rainforests. That's why the observations of Humboldt, Darwin, Wallace, and others were so important. A few months ago I wrote about the importance of the comparative method to biological inquiry, and here is comparison writ large: different parts of the world, different climates, different geographies.
It seems to be no coincidence that many of those associated with the theory of evolution had experience on long ocean voyages during which they visited many different types of ecosystems. And this doesn't hold for British biologists alone: the great German champion of evolution, Ernst Haeckel, managed to at least get to the Canary Islands, where he studied his beloved jellyfish (Richards, 2008). Great 20th-century evolutionists were also travelers. George Gaylord Simpson studied South American fossils, Ernst Mayr did his early work on New Guinea birds, and, more recently, E. O. Wilson did research on South American ants. While I am not arguing that the biologists of the future should hit the road, it does seem that travel can be an important element in the education of a biologist.
I work at an institution whose present strategic plan has the development of global education as one of its key goals. Study abroad is encouraged and, I might say, pushed. A related part of the plan is to infuse more international perspectives into on-campus courses. Since this has always been a cornerstone of biology education, I am more than happy to comply. Encouraging study abroad is a different issue, considering that nearly half of our undergraduates come from households with incomes below the poverty level. I just don't feel comfortable doing it. But then I read about Huxley and Wallace and the others who apparently benefited so greatly from their travels. Our institution does try to provide study-abroad scholarships for needy students, so we are at least making an attempt to, as our administration loves to say, “level the playing field.” I guess I can say that writing this column has made me a little less queasy about suggesting world travel. At the very least, I can lead students on a geographic exploration of evolution, much as McCarthy does, and hope that attention to diverse ecosystems will spark their desire to explore the world.
She earned a B.S. in biology from Marymount Manhattan College; an M.S., also in biology, from Boston College; and a Ph.D. in science education from New York University. Her major interests are in communicating science to the nonscientist and in the relationship between biology and art.