| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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reviews Leaps of Evolution At the Water's Edge: Macroevolution and the Transformation of Life, by Carl Zimmer. The Free Press, New York, 1998, 304 pp., $25.00 cloth. While scuba diving off Grand Bahama, Carl Zimmer simultaneously comes to grips with his aquatic inadequacy, compared with the snapper and dolphins swimming around him, and comes to appreciate his place in evolution. This dive, he realizes, is a family reunion for three disparate kinds of vertebrates whose pedigree extends back more than half a billion years. So begins this engaging exploration of "the twin stories of how vertebrates came ashore and returned to the sea." Rather than the minutiae of how natural selection operates from one generation to the next, Zimmer, an award-winning science writer and an editor of Discover magazine, is more concerned here with the "longer, grander scale" of macroevolution. He focuses on two major transitions in vertebrate history: how fish became four-footed landlubbers called tetrapods, and how some wolf-like mammals evolved into whales and dolphins. Until recently, each of these stories could only be told with plenty of long, awkward pauses, but the last decade alone has seen a number of critical new fossil finds, and a remarkable convergence of evidence from paleontology, embryology, and genetics that now make for a fuller, more compelling account. The tale of tetrapods, a group that includes amphibians and amniotes, begins around 370 million years ago. It remains unclear exactly what prompted some successful marine species to try their hand--well, lobefin foot--in such an alien place as dry land, but Zimmer questions the traditional scenarios and presents some evidence for other possibilities. Much of this portion of the book portrays the various fossil characters that played a role in making the switch. There's Elginerpeton, the oldest and most primitive known tetrapod, which was recently rescued from more than a century of obscurity collecting dust on an Oxford museum shelf. With a pointy snout and oars for legs, Elginerpeton may have rowed around in water but may not have been quite up to walking. From Greenland, there's Acanthostega, another intermediary, with a broad, flat head and four limbs but which breathed through gills and retained the lateral line sensory system of fish. Its legs may have aided ambushing prey in shallow water. Both these creatures show that some of the basic tetrapod body parts, including limbs, evolved first in water, and must have had another use well before anyone rowed or pulled itself ashore. A host of other extant and extinct critters--Eusthenopteron, Ichthyostega, lungfish, coelacanths, Basilosaurus, Ambulocetus--fill out the tetrapod and whale sagas. Zimmer relates the background of each discovery, from Pennsylvania to Pakistan. Pen-and-ink illustrations flesh out many of the players and display their relationship to living species. He excels at portraying the scientists who helped write these particular chapters in evolutionary theory. Readers meet British anatomist Richard Owen, Darwin's arch-rival, with "the kind of brown-eyed glare on which old failed prophets usually have a monopoly." And French paleontologist Baron Georges Cuvier, who by age 30, and despite a disbelief in evolution, had invented the modern study of paleontology. Balzac wrote that Cuvier could evoke "worlds from a whitened bone" and "cities from a tooth." Besides these historical figures, Zimmer characterizes the contemporary researchers who are refining our understanding of vertebrate evolution. Interspersed with these accounts are concise, though occasionally complicated, lessons on such topics as dolphin echolocation, Hox genes (which guide the development and placement of body parts in animal embryos), and cladistics, a novel technique for ascertaining evolutionary relationships that has eclipsed traditional approaches to taxonomy. "In the reconstruction of life's history, taxonomy might seem as crucial as taxidermy," writes Zimmer. "In fact, it is the skeleton on which the body of evolutionary biology hangs. Ultimately, Zimmer cannot conclude whether macroevolution--such dramatic shifts as hands replacing fins or flukes subsuming feet--proceeds in a similar fashion to microevolution due to natural selection. Were these changes slow, sudden, or both? Despite this shortcoming, At the Water's Edge is a richly rendered look at how knowledge in the natural sciences builds and how scenarios spun from such knowledge get revised. It reveals that there are many evolutionary stories worth knowing, and retelling, besides our own. Recomended Reading The Passionate Observer: Writings from the World of Nature, by Jean-Henri Fabre, watercolors by Marlene McLoughlin. Chronicle Books, San Francisco. 1998, vii+133 pp., $21.95 cloth. Born in France in 1823, Jean-Henri Fabre is the naturalist par excellence. Victor Hugo called him "the insects' Homer," and Charles Darwin "an incomparable observer." But the title of this book, a translation of his Souvenirs Entomologiques, describes him best, though even that does not do justice to his exquisite writing style. What the original must be like it's hard to imagine, because the translation explores the insect world in such a comprehensive, comprehendible, and utterly engaging way, that it is hard to put down. If there was ever a book to read on a lazy day in the garden, this is it. Each plant and, especially, each insect, that surrounds you will emerge like a Shakespearean character to strut its magnificent hour in the sun. Even the unread pages are welcoming, thanks to the elegant watercolors of Marlene McLoughlin. Encyclopedia of Dinosaurs, edited by Philip J. Currie and Kevin Padian. Academic Press, San Diego, 1997, 869 pp., $125.00 cloth. Our fascination with dinosaurs cuts across cultural and geographic boundaries and infects all ages. In his foreword to this exhaustive tome, Michael Crichton recounts how when he first began writing a dinosaur-based novel in 1981, he set it aside to wait until the public's dinomania died down. It never did, and now Crichton as much as anyone has assured that it won't anytime soon. The Encyclopedia of Dinosaurs will surely keep any dinophile occupied for weeks. Academy Fellow Kevin Padian and co-editor Phil Currie assembled an all-star array of paleontologists to write the 275 entries: John Horner, Paul Sereno, Mark Norell, Martin Lockley, and the editors themselves, to name a few. The nine general subject areas include kinds of and groups of dinosaurs, their biology, environments, and geological context, plus famous fossil sites, expeditions, museums or research institutions, and techniques used to study the prehistoric beasts. The entries range in length from one paragraph to several pages. Longer articles tackle broad thematic issues. Each entry ends with a bibliography for anyone wishing to excavate further. To give a taste of the range of subjects, under "B" one finds essays on dinosaur behavior, biogeography, bipedality and bird origins (both written by Padian), and braincase anatomy. Illustrations include black-and-white photos and diagrams, plus four short sections of color plates, which mainly depict fossil sites and painted dinosaur reconstructions. Given the interest in the topic, it's no surprise that this book has its own Internet home page with details on the encyclopedia and links to dinosaur sites of the cyber rather than fossil variety. Saving the Marin-Sonoma Coast: The Battles for Audubon Canyon Ranch, Point Reyes, and California's Russian River, by L. Martin Griffin. Sweetwater Springs Press, Healdsburg, 1998, 294 pp., $45.00 cloth, $29.95 paper. It's easy to take the coastal counties north of San Francisco for granted. But its no accident that minutes after crossing the Golden Gate space opens up and time slows down. It could easily have been otherwise, as Harold Gilliam reminds us in his foreword to Martin Griffin's Saving the Marin-Sonoma Coast. San Fransisco could have gone the way of Los Angeles after WW II, sprawling out in every direction. Indeed, developers nearly realized plans to put malls and freeways on the east shore of Tomales Bay, to fill Bolinas Lagoon, to build a city, Marincello, on the Marin Headlands, and to lop off the top of Ring Mountain and dump it in Richardson Bay to make a surface on which to build a giant subdivision, and so on. Instead, two-thirds of Marin is protected as more or less permanent open space, wildlife preserves, parks, and farmland. Griffin, a physician and public health official by vocation and conservationist by nature, is a central player in nearly all of the land use battles he describes. Along with his friends Caroline Livermore and Stan Picher, Griffin transformed Marin land use politics from gung-ho, no-holds-barred growth, to one of the lowest growth, most conservation-oriented counties in the country. But Griffin's is not only a story of victories; it is also a story of what was lost--the battle against Warm Springs Dam, for instance--and a description of what remains vulnerable. As Griffin points out, conservation victories are always temporary, though conservation defeats are often permanent. The accomplishments detailed here are inspiring and substantial, but we would do well to remember that the story of land use struggles in Marin and Sonoma has only just begun. To quote Gilliam again, the book "affirms a message that should be shouted from the housetops: citizens working together have the power to shape the course of events that affect their lives. In a time of cynicism about the workings of democracy, there is no message more urgent." Sierra Nevada: The Naturalist's Companion, by Verna Johnston. University of California Press, Berkeley, 1998, 207 pp., $29.95 cloth. Lovers of the Sierra will be hard-pressed to find a more informative and engaging traveling companion than Verna Johnston. In her revised Sierra Nevada, an update and expansion of her 1970 edition, she leads us from the mixed forest and chaparral of the foothills, through the mid-mountain conifer region, past glacier-carved canyons lined with red firs and lodgepole pines, stopping in the giant sequoia groves, pressing on to the treeline and the alpine crests, then dropping precipitously to the Great Basin desert. A long-time biology professor as well as an ornithologist, Johnston brings knowledge and impish delight to the plant belts or "life zones" she explores. Also an accomplished photographer, she includes a portfolio of Sierran plants and animals, the captions gracefully weaving the photos into her text. Her notes on Native American land use, pollution, fire ecology, and the consequences of expanding human habitation add somber notes to her story. But the most memorable episodes are her portraits of specific residents of this remarkable and diverse region, of wood-pewees "dart[ing] about, snapping mandibles on deadly moths" and "a fat, grizzled yellow-bellied marmot, stretched out on a boulder, basking in the sun." |
Summer 1998
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