March 22, 2010 12:48:00 PM
Rob Hardy - [email protected]
Some animals like to sport bright colors, as if they want to be seen. Others favor drab colors, as if they want to blend in and avoid recognition. There must be advantages to both strategies. Soldiers used to sport bright red clothing in the field, and now tend to go with grey and olive blotches, if they are in forest, and beige spotty patterns if they are on sand.
The invisible hand of evolution is at work in the natural world and the visible one of tacticians is at work in the military one, both hands working on the vital competition of appearances. There aren''t so many soldiers who are still trying to stand out, but the animals who do so, and plenty of soldiers and sailors and animals who try to blend in, all come under the attention of "Dazzled and Deceived: Mimicry and Camouflage" (Yale University Press) by Peter Forbes.
The effort toward understanding military and natural camouflage has been not just separate efforts by naturalists and soldiers, but combined work in the field, joined also by artists and even a magician. Just as you would suspect, there are plenty of surprises in this book, along with a fine introduction to the evolution of mimicry down to the current biochemical understandings.
Forbes spends much of the book on butterflies. Before Darwin had published "The Origin of Species," he had published the much-admired and popular "The Voyage of the Beagle." Two young men, fans of the book and aspiring biologists, set out to travel up the Amazon to make their own discoveries. They were Henry Bates and Alfred Russel Wallace, poor men who had taught themselves some biology through the Mechanics'' Institutes.
Wallace would go on to make discoveries in South America and Indonesia that would lead him to theorize the principles of evolution, already worked out by Darwin but only published by after long reluctance when Wallace himself was about to publish; they did so jointly. Among Bates''s discoveries were the cabbage white butterflies Leptalis, which used camouflage in a way not previously understood. They mimicked the bright colors and patterns of another butterfly, the Heliconidae. What was the advantage of looking like another butterfly? Bates showed that the imitated Heliconidae sported bright colors as a sort of warning; it wanted to be seen and recognized, because it tasted bad and was unpalatable. The more recognizable it was, the more often bird predators would leave it alone.
But Leptalis, on the other hand, was tasty. It displayed the warning colors and markings of Heliconidae, but in the case of Leptalis, the warnings were false. False or true, the warnings helped give each butterfly a better chance of surviving and passing on its genes. The false imitation warnings were complicated enough (and occur in other species like snakes, not just insects), but there were true imitation warnings as well. A German naturalist, Fritz Müller, was also collecting in the jungles of South America, and noticed that unrelated species of bad-tasting butterflies (and even moths) shared colors and markings. He went on to show in a mathematical way that it was to the advantage of unpalatable species to look the same; their true warnings reinforced each other every time a bird tried to eat one and learned how bad a creature with such appearance tasted. Müller, Bates, and Wallace all came to see that this sort of mimicry, along with the more familiar sort of bugs looking like sticks or leaves (or, in other cases shown here, flower parts or even bird droppings) were part of the continuum of change driven by evolution.
In the 1890s, a cranky New England painter burst into the realm of naturalists who were concerned with camouflage and mimicry. Abbott H. Thayer thought that only an artist could rightly appreciate the profundity of the deceptive pictures made by birds and animals. He insisted that even the brightest displays were for the purpose of hiding the animal; he painted a peacock, for instance, to show how its spectacular tail might blend in with a mosaic of greenery, and its blue neck with the sky. He also said flamingos sported their pink to blend in at sunrise and sunset. He obsessively insisted that coloration was for no other purpose than to obscure the animal; he didn''t accept that colors might be bright for the purpose of warning.
He might have gone too far, but he had a scientific law named after him: Thayer''s Law of Concealing Coloration says that animals are countershaded, with dark tones on their backs blending to pale ones on the belly so that light and shade might even each other out and the animal might remain obscure. He was dogmatic and pugnacious about his discoveries of coloration, and took it upon himself to advise the US Navy about how to disguise its ships during the Spanish-American War. His ideas were ignored, but he did patent the idea of countershading ships, and went on to design disruptive coloration for them. He teamed with the Scots zoologist John Graham Kerr to have British ships painted in "dazzle" patterns, bold darks and lights that obscured the form of the ship and even made it look as if it were on a different heading from its true one.
An artist from the Vorticist school, Edward Wadsworth, was recruited to help execute the schemes. No one really knows if the paint schemes saved any ships, but they did prove to be distinctive and they helped sailors'' morale. Trying to hide as big an object as a ship was probably impractical, and anyway, radar eventually came along and paid no attention to such superficialities as paint. The interplay, however, between military tacticians, naturalists, and artists (which, given the personalities involved, was often angry) gives Forbes a background to tell a broad story about camouflage, including how tanks were hidden in the African campaign of World War Two, and how the flamboyant magician Jasper Maskelyne helped troops and equipment disappear (or was it all hocus-pocus?).
Much of Forbes''s book describes the science and scientists working out how chromosomes have activated the chemistry that, for instance, turns inheritance into particular wing colors. There are good profiles of artists and scientists. It is a pleasure, for instance, to read about Miriam Rothschild, who was a member of the famous banking family, and used some of her fortune to equip a laboratory in her home where she investigated how inedible monarch butterflies got their toxins.
She worked out how caterpillars evolved an invulnerability to toxins of particular milkweed plants, and not only did this make the plants their particular field of forage, they absorbed the toxins into their own systems to make them toxic in turn. She tested the toxins on starlings -- the birds vomited. Forbes also reviews the case of the peppered moth, which famously darkened in color during the decades when soot was covering the landscape, only to lighten when the environment became cleaner. Creationists have attempted to show that the original research was deliberately slanted to make a case for evolution, but Forbes shows that whatever flaws the original research did have, recent research has confirmed the case that this example of evolution should be part of biology teaching.
He explains how the animal most famous for blending in, the chameleon, actually is more likely to change its colors for the purpose of standing out, like for signaling aggressiveness between males. He writes admiringly of the best trickster in nature, the octopus, that "compendium of every camouflage and mimicry technique known." Ranging into art, military tactics, field biology, evolution, and biochemistry, Forbes has given a unique look into the hidden techniques of natural and artificial camouflage. Natural and artistic and military techniques, he shows, don''t follow any particular advancement or grand design; they all in their fashion take their chances, make choices, and do experiments.
Rob Hardy is a local psychiatrist who reviews books for a hobby. His e-mail address is [email protected]