autumn books forced him to become a eugenist. Experience preference to settle on backgrounds that equally seemed to suggest what should be matched its colour. done. Sterilization was, he thought, a suspect Criticisms of this story have circulated in option — after all, civil liberties were central samizdat for several years, but Majerus sum- to American values. The way forward must marizes them for the first time in print in an lie in the institutional segregation of the absorbing two-chapter critique (coinciden- unfit. Not only would that prevent defectives tally, a similar analysis [Sargent et al., Evol. from breeding and create a supportive and Biol. 30, 299–322; 1998] has just appeared). humane environment for them, but it would Majerus notes that the most serious problem provide a superb “human laboratory” (God- is that B. betularia probably does not rest 8on dard’s standard phrase) for researching their tree trunks — exactly two moths have been mentalities and laying bare the pathology of seen in such a position in more than 40 years the human psyche. of intensive search. The natural resting spots It would, as Zenderland persuasively are, in fact, a mystery. This alone invalidates argues, be misleading to cast Goddard sim- Kettlewell’s release–recapture experiments, ply as some sort of stock bigot. Doubtless he Cautionary tale: the classic account of industrial as moths were released by placing them believed there was some kind of underclass, melanism in the peppered moth now looks flawed. directly onto tree trunks, where they are but he was remarkably free of racial and highly visible to bird predators. (Kettlewell colour prejudice — what he mainly feared Michael Majerus’s book, Melanism: Evolu- also released his moths during the day, while were poor whites. He is best seen primarily as tion in Action. Depressingly, Majerus shows they normally choose resting places at a representative of an emergent cadre of that this classic example is in bad shape, and, night.) The story is further eroded by noting experts, scientists and professional adminis- while not yet ready for the glue factory, needs that the resurgence of typica occurred well trators, anxious to establish a place in the sun serious attention. before lichens recolonized the polluted trees, for themselves as the new priesthood serving According to the standard textbook and that a parallel increase and decrease of a secularizing society, preaching the gospel litany, before the mid-nineteenth century, all the melanic form also occurred in industrial not of laissez-faire capitalism but of B. betularia in England were white moths areas of the United States, where there was no informed social responsibility. peppered with black spots, a form called typ- change in the abundance of the lichens that Zenderland does not pretend that her ica. Between 1850 and 1920, typica was large- supposedly play such an important role. protagonist was a very profound or original ly replaced by a pure black form (carbonaria) Finally, the results of Kettlewell’s behav- thinker. Although a passionate champion of produced by a single dominant allele, the fre- ioural experiments were not replicated in ubiquitous intelligence testing, Goddard quency of which rose to nearly 100% in some later studies: moths have no tendency to never seems to have thought deeply about areas. After 1950, this trend reversed, making choose matching backgrounds. Majerus what precisely it was that was being mea- carbonaria rare and typica again common. finds many other flaws in the work, but they sured. He was a doer, a technician, lucky These persistent and directional changes are too numerous to list here. I unearthed enough to hold in his hands, in the Binet test, implied natural selection. In a series of stud- additional problems when, embarrassed that device utterly appropriate to the needs of ies, this conclusion was verified by several at having taught the standard Biston story classification and control in a mass society. investigators, most prominently Bernard for years, I read Kettlewell’s papers for the Roy Porter is at the Wellcome Institute for the Kettlewell of Oxford. first time. History of Medicine, 183 Euston Road, London According to these workers, the evolution Majerus concludes, reasonably, that all NW1 2BE, UK. of colour was caused by birds eating the moths we can deduce from this story is that it is a most conspicuous on their normal resting site case of rapid evolution, probably involving — tree trunks. The increase in black moths pollution and bird predation. I would, how- was attributed to pollution accompanying the ever, replace “probably” with “perhaps”. B. Not black and white rise of heavy industry. A combination of soot betularia shows the footprint of natural Melanism: Evolution in Action and acid rain darkened trees by first killing the selection, but we have not yet seen the feet. by Michael E. N. Majerus lichens that festooned them and then blacken- Majerus finds some solace in his analysis, Oxford University Press: 1998. 338 pp. £55, ing the naked trunks. The typica form, previ- claiming that the true story is likely to be $105 (hbk), £23.95, $45 (pbk) ously camouflaged on lichens, thus became more complex and therefore more interest- Jerry A. Coyne conspicuous and heavily predated, while the ing, but one senses that he is making a virtue less visible carbonaria enjoyed protection and of necessity. My own reaction resembles the From time to time, evolutionists re-examine increased in frequency. After the passage of dismay attending my discovery, at the age of a classic experimental study and find, to their the Clean Air Acts in the 1950s, trees regained six, that it was my father and not Santa who horror, that it is flawed or downright wrong. their former appearance, reversing the selec- brought the presents on Christmas Eve. We no longer use chromosomal polymor- tive advantage of the morphs. This conclusion Occupying a quarter of the book, the Bis- phism in Drosophila pseudoobscura to was bolstered by a geographical correlation ton analysis is necessary reading for all evolu- demonstrate heterozygous advantage, between pollution levels and morph frequen- tionists, as are the introductory chapters on flower-colour variation in Linanthus parryae cies (carbonaria was most common in indus- the nature of melanism, its distribution to illustrate random genetic drift, or the trial areas), and most prominently by Ket- among animals, and its proposed causes. viceroy and monarch butterflies to exemplify tlewell’s famous experiments which showed Majerus, however, designed his book for Batesian mimicry. Until now, however, the that, after releasing typica and carbonaria in both professional and lay readers, and this prize horse in our stable of examples has both polluted and unpolluted woods, causes some unevenness in the material. The been the evolution of ‘industrial melanism’ researchers recaptured many more of the Bistonstory is sandwiched between less com- in the peppered moth, Biston betularia, pre- cryptic than of the conspicuous form. The dif- pelling chapters, including long sections on sented by most teachers and textbooks as the ferential predation was supported by direct the basic principles of genetics and evolu- paradigm of natural selection and evolution observation of birds eating moths placed on tion, which can be skipped by evolutionists. occurring within a human lifetime. The re- trees. Finally, Kettlewell demonstrated in the Other discussions, involving melanism in examination of this tale is the centrepiece of laboratory that each form had a behavioural ladybirds and other Lepidoptera, as well as NATURE | VOL 396 | 5 NOVEMBER 1998 | www.nature.com 35 Nature © Macmillan Publishers Ltd 1998 autumn books the author’s unpublished work on habitat strategy operates. The issue tackled is a fun- selection, are full of technical details that will damental puzzle in depth perception: “The overwhelm the lay reader. Unfortunately, image at the eye has two dimensions; there- most of the work described is inconclusive; fore it has countless interpretations in three despite the widespread occurrence of dimensions.” Hoffman then solves (most of) melanism, its evolutionary significance is the problem of how the visual system comes nearly always unknown. to the correct interpretation (most of the What can one make of all this? Majerus time) by conjecturing an ordered sequence concludes with the usual call for more of visual rules. These range from the simple research, but several lessons are already at “Always interpret a straight line in an image8 hand. First, for the time being we must dis- as a straight line in 3D” to the considerably card Biston as a well-understood example of less obvious “Interpret each concave point natural selection in action, although it is on a bound as a saddle point on a rim”. clearly a case of evolution. There are many Hoffman leads the reader through the studies more appropriate for use in the class- justification for these maxims by showing room, including the classic work of Peter and The “subjective” Necker cube: the black discs can with line drawings and other two-dimen- Rosemary Grant on beak-size evolution in be seen as behind the cube or as holes in front of it. sional patterns exactly how each rule serves Galapagos finches. It is also worth pondering to constrain the percept that we actually why there has been general and unques- that Donald Hoffman’s riveting introduc- derive from the image. In other chapters, tioned acceptance of Kettlewell’s work. Per- tion to Visual Intelligence contains very little Hoffman deploys essentially the same strat- haps such powerful stories discourage close about brains. Even when he describes how egy to show how the visual system recovers scrutiny. Moreover, in evolutionary biology brain damage can cause loss of colour per- surfaces, shapes and their parts, colour, and there is little payoff in repeating other peo- ception or of motion perception, Hoffman the path of moving objects by “an intelligent ple’s experiments, and, unlike molecular has his eye more on the functional ramifica- process of active construction”.