The Deceptional Life
DAZZLED AND DECEIVED: Mimicry and Camouflage. Peter Forbes. xvi + 283 pp. Yale University Press, 2009. $27.50.
With few exceptions (the blue sky being one), the physical world is pretty drab—earth tones predominate. By contrast, living nature is profligate with color, and those colors often appear in patterns that catch the eye. How is it, then, that colorful creatures have survived, given that it presumably is not an advantage for predators and prey to advertise their presence to one another?
Charles Darwin had little to say about this paradox in On the Origin of Species. But he believed that natural selection, if correct, would be universally applicable, and he sought explanations for any apparent exceptions. So he was receptive when Henry Walter Bates initiated a correspondence shortly after the Origin appeared. Bates, who had spent much more time than Darwin in the Amazon, had noticed that butterflies of different lineages often exhibit almost indistinguishable color patterns. He theorized that defenseless species gained protection from potential predators by taking on the pattern and coloration of another species that has some sort of defense—a quality that makes it inedible, perhaps—for which its appearance serves as a warning. This process, now known as Batesian mimicry, confers a selective advantage as long as the mimicking species remains scarcer than its model.
Peter Forbes’s Dazzled and Deceived, which is both a natural history and a cultural history of mimicry and camouflage, opens with a description of Bates’s travels in the Amazon with Alfred Russel Wallace in 1848. Forbes then retells the story of the discovery of natural selection by Darwin and Wallace, giving an account of communications among the three naturalists and explicating their views on mimicry as they developed.
Bates noticed that it wasn’t just the defenseless species that mimicked the unpalatable ones—unpalatable species mimicked each other. Another of Darwin’s correspondents, zoologist Fritz Müller, recognized the principle operating in this situation—that there is an advantage to be gained if different species pool their mimetic resources. If several unpalatable species look alike, that will reduce the chance that any one of those species will lose many individuals to young predators who haven’t learned yet to connect the warning coloration to bad-tasting prey. So to Batesian mimicry we add Müllerian mimicry and the general concept of mimetic complexes.
By the end of the 19th century, numerous examples of animals mimicking both plants and each other had come to light, and the notion was no longer novel. At the end of a long paragraph in The Butterfly Book (1898), the author, W. J. Holland, refers the curious reader to “the writings of Mr. Alfred Russel Wallace and Mr. Darwin, who have written at length upon mimicry among butterflies,” making no mention of Bates or Müller. In his 1890 book The Colours of Animals, Edward Bagnall Poulton produced a general categorization of the biological roles of coloration, and the subject gained the attention of various anti-Darwinians—a sign then, as now, that it had attained main-scene status.
In the early part of the 20th century, geneticists’ worries about how natural selection for mimesis might get under way made the picture muddier. In 1915, Reginald Punnett wrote a prescient book, Mimicry in Butterflies, in which he observed that many butterfly genera are not mimetic, because their developmental mechanisms do not facilitate the necessary pattern formation.
At this point the purview of Forbes’s book expands beyond biology as he begins to discuss the ideas and work of the eccentric and opinionated New England painter, Abbot Thayer. Artists had begun to recognize that there must be some underlying reason that organisms have the colors and patterns that they do, and in 1909, Thayer wrote a fairly intemperate book on coloration in nature. He dismissed mimicry but made a central biological principle of disruptive color patterns and concealment. He tried, unsuccessfully, to sell the military on what we would now call biomimetic camouflage, and he earned the enmity of Theodore Roosevelt.
By the time of the First World War, at least three communities cared about nature’s visual patterns: biologists, artists and the military. These were groups whose mindsets were far from compatible. The biologists still found the perfection of mimicry hard to reconcile with genetics and evolution. The artists saw evolution in distinctly metaphysical terms. And the military, traditionally conservative, distrusted civilians’ offers of quick fixes as well as the decidedly evangelical individuals in the other two groups.
Nonetheless, by the war’s end both the Americans and the British were making military use of concealing patterns and what the British called “dazzle” patterns (this was probably Thayer’s term originally). Dazzle, used primarily on ships, employed the supposed (and still uncertain) trick of the zebra—breaking up dark areas with patches of white to generate either no recognizable pattern or a deceptive one. Ideally, an observer, perhaps looking through a periscope, would not know whether a ship was coming or going. But in the end, dazzle camouflage had only minimal success. Camouflage on land, both more significant and more successful, drew not on natural history but on traditional garb for stalking animals and on the new cubist art.
Between the wars, biologists continued searching for the mechanisms that create patterns. There were squabbles between neo-Darwinian incremental geneticist R. A. Fisher and the zoologist Richard Goldschmidt, who believed that large evolutionary leaps could occur. Meanwhile, some biologists began to suspect that great changes in appearance could be based on much less radical genetic alteration, providing what has become the basis for reconciliation between the views of Fisher and Goldschmidt. At the same time, some surrealists saw nature as the source of their style, and both the antigeneticist Trofim Lysenko and the anti-Darwinian lepidopterist and novelist Vladimir Nabokov weighed in.
The zoologist Hugh Cott had the final word in Adaptive Coloration in Animals (1940), a definitive synthesis of everything known about camouflage and mimicry in nature. Cott ruffled fewer feathers, and his well-organized and unfanatic ideas proved militarily effective, even under the scrutiny of improved techniques for target detection. Thayer’s principles reemerged in more temperate and rational terms, and camouflage schemes based on them survived both photometric analyses and enemy encounters. Biomimetic camouflage took its place as yet another technique in a sophisticated armamentarium of visual deceptions.
But did visual deception really influence the evolution of living forms? The famous postwar experiments of Bernard Kettlewell on industrial melanism in peppered moths made a strongly positive case. Moths of that species took on a dark form in areas of Britain where the trees were darkened by industrial pollution, and birds were less successful in detecting the melanic forms there than in unpolluted areas. Kettlewell’s methodology later came in for criticism, but the basic idea now seems fairly secure.
With many more eccentric players than I’ve mentioned, Dazzled and Deceived tells a fine story. It is a delight; only when briefly tackling the molecular genetics of mimicry does Forbes have difficulty holding the reader. I am, though, a little uncomfortable with his repeated assertion that biology is the science of special cases. What the field has, instead, is a mind-numbing multidimensionality that exceeds that of other sciences. Oversimplified analysis is a worse hazard for the biological baby than for the physical bathwater.
Dazzled and Deceived does not tell the whole story. Largely or entirely omitted are the problems of animals in the open sea, on which considerable work has been done. Also missing are the important things that mimicry tells us about the sensory savvy of predators. Nor does Forbes note that some forms of display (including, perhaps, the peacock’s tail feathers) may be explained by Amotz Zahavi’s “handicap principle”—that surviving with some functional disability indicates superior fitness to potential mates. And almost no mention is made of deception that is auditory, olfactory or tactile, rather than visual.
Such caveats aside, I unhesitatingly recommend the book to both scientists and nonscientists.
Steven Vogel, emeritus faculty member in biology at Duke University, is the author of several books, including Cats’ Paws and Catapults: Mechanical Worlds of Nature and People (W. W. Norton, 1998) and Glimpses of Creatures in Their Physical Worlds (Princeton University Press, 2009).
» Post Comment