Civilization and the Limpet

Natural History, Nov, 1998 by Steven Austad

CIVILIZATION AND THE LIMPET, by Martin Wells. Perseus Books (Helix Books), $22; 224 pp.

Review

One of the challenges and satisfactions of scuba diving is mastering that state of grace known as neutral buoyancy, in which one floats effortlessly upside down or sideways, neither ascending nor descending--the way astronauts float in space capsules. Maintaining neutral buoyancy is nearly impossible for humans. Even tiny errors in adjustment get exaggerated. A bit too much air intake in your balloonlike buoyancy-control device, and you slowly begin to ascend. Ascending reduces the water pressure, causing the air providing your buoyancy to expand, so you rise ever faster. Another error could start you descending instead, and you would soon be hurtling downward into the abyss.

So when we dive, most of us remain at our chosen depth by actively, inelegantly flapping our arms and legs. Like human divers, most marine creatures prefer to spend their lives suspended somewhere between the surface and the seafloor; in other words, they are also well served by a mastery of neutral buoyancy. As Martin Wells reveals in one essay in his new book, the various ways they do so not only are fascinating but also help explain why fish from the depths are usually D.O.A. on a trawler's deck, and why deepwater squid are never found on your sushi plate.

Wells is a zoologist, diver, yachtsman, and keen observer of generally underappreciated sea creatures, particularly those--such as jellyfish, lugworms, and limpets--that lack joints, jaws, backbones, and teeth large enough to terrorize teenage moviegoers. Like all good zoologists, he values animals for more than their inherent charm: he understands how they are constructed, can decipher their evolved solutions to special environmental problems, and tries to imagine what their sensory world might be like. Unlike most zoologists, however, he has a flair for connecting his professional insights, in interesting ways and then relating them to aspects of life beyond science. He also enjoys communicating these insights and connections to more casual observers of the natural world.

In his title essay, Wells begins by asking a straightforward question: How do limpets find their way back from their favorite algal dining spots to their home niche among the intertidal rocks? He then proceeds to consider why snails, worms, and even octopuses, with all their formidable intelligence, cannot learn, as arthropods and vertebrates do, to navigate mazes or distinguish the three-dimensional shapes of objects by feeling their outline. The answer turns out to be that creatures need movable joints to measure distances accurately and to be able to repeat movements precisely. He finishes the essay with an appreciation of how animals' ability to measure distances is a necessary condition for navigating by the stars (and by compass) or for building computers or civilizations. The pleasant thing about such essays is that as you learn a bit about the animals, the provocative connections invoked also stimulate novel thoughts.

Wells is a zoologist of the physiological variety, and his most successful essays have a physiological theme. He discusses warm-blooded fishes, the hows and whys of animal luminescence, the costs and advantages of jet propulsion, and how diving mammals avoid the bends. But he also weighs in on nonphysiological issues, such as life on islands, the politics of over-fishing, animal rights, and why there are two sexes rather than one or ten.

Wells has a spare, informal writing style and a good sense of metaphor (he describes the hard-shelled mollusks' defense when they "pull back into the castle and slam the door" as a "medieval tactic"). For those who may have forgotten that the British and Americans are indeed two peoples separated by a common language, this book will remind them. For Americans, the Anglicisms provide as much off-center charm as does the subject matter. Wells loves those marvelous Anglo-Saxon terms such as "knackered" or "scuppered," which, alas, have never become popular on this side of the Atlantic. He also enjoys dispensing practical advice on everything, including how to avoid venomous sea creatures, how to cheat on a Breathalyzer test (hint: try hyperventilating), and the best way to pick up an octopus or cook a mackerel.

I admit that his talent for concise summaries of physiological principles makes me envious. My guess, however, is that this talent may occasionally leave the physiologically unsophisticated reader behind. For instance, he disposes of the fallacy c)f comparative strength--the idea that because an ant can hoist a leaf twenty times its body weight, one the size of a person could walk off with your sport utility vehicle--in a mere handful of words: "The force a muscle can exert depends on its cross section, not its volume. Volume is a cubic measurement, so the ratio of cross section to mass rises as you shrink." That's a concise and accurate description, but there's a lot in it to unpack.