Nabokov and Mimicry^[1]

 

For Nabokov, mimicry in nature was a source of constant wonderment. The fascination with observable detail as well as with disguise and deception was also one of the tangible links between his fiction and his entomological work. As late as 1952, four years after he had given up his Research Fellowship at the Harvard Museum of Comparative Zoology and with it his laboratory work, Véra Nabokov wrote to a publisher:

The question of mimicry is one that has passionately interested him all his life and one of his pet projects has always been the compilation of a work that would comprise all known examples of mimicry in the animal kingdom.^[2]

Indeed, in one of his earliest poems, written 1919, he has a zoologist "defended a big dissertation on mimicry". We are perhaps fortunate that he himself resisted the temptation. There is mimicry not just in butterflies and moths but in many other insects, in reptiles, in fish, even in birds; there is visual, auditory, chemical, tactile and behavioral mimicry. In fact, it is such a ubiquitous phenomenon in animals which have no other defenses that Nabokov could well have devoted the rest of his life to it without ever coming to an end, leaving his literary work  unwritten.

Considering how much he cared about mimicry, it is surprising how little he wrote about it and how few specific cases he commented upon. It is true that early in 1942 he composed an essay enticingly titled "Mimicry in Theory and Practice". It impressed Edmund Wilson who suggested journals to send it to and seems to have delighted several audiences, among them the Cambridge Entomological Club where he read it on April 12, 1943 – "… a reading the entertaining informativeness and clarity of which these prosaic minutes could hardly attempt to capture", says the secretary in his minutes of the evening.^[3] Unfortunately, the paper was never published and the typescript seems to be lost. Given the fact that in a letter to Mark Aldanov^[4] Nabokov mentioned that the piece was to be "a furious refutation of 'Natural Selection' and the 'struggle for life'", one may assume that it mirrored the argument Nabokov had put forth in his second addendum to The Gift, written in 1939 ("Father's Butterflies", first published in that cornucopia, Nabokov's Butterflies, 2000). So we are left without a systematic treatment of the matter and have to put up with two largely overlapping passages in The Gift and Speak, Memory (fully compatible with the reasoning of "Father's Butterflies") and a few casual mentions and remarks.

Most of the cases Nabokov mentioned may go back to a book by Arnold Jacobi that focused on mimicry in butterflies and moths and at the time was surely available in Berlin libraries.^[5] It adhered to a strictly Darwinian point of view. Nabokov's few additional cases come from diverse sources or were purely imaginary; some were misunderstandings.

There would be no point in collecting examples of disguise and deception from Nabokov's fiction and pretending they owe their existence to the author's involvement with mimicry in butterflies. It would be all too easy to argue that we are faced with a case of mimicry when, in the full version of the Lolita screenplay, Quilty puts on the mask of a bearded local train robber to abduct Lolita from Humbert's motel room. Butterflies mimic some object or some other butterfly to avoid predators. In the Lolita screenplay, it is the predator (Quilty) who is the mimic, the model (the train robber) does not frighten people any more and is a popular source of merriment, and the prey (Lolita) is not deceived but colluding and wants to be eaten. It would be absurd to term this mimicry even in a loose metaphorical sense.

So let me rather come to the heart of the matter right away, and that is mimicry as a link between nature and art. These are the two central passages.

From The Gift:

... the incredible artistic wit of mimetic disguise ... was not explainable by the struggle for existence (the rough haste of evolution's unskilled forces), was too refined for the mere deceiving of accidental predators, feathered, scaled and otherwise (not very fastidious, but then not too fond of butterflies), and seemed to have been invented by some waggish artist precisely for the intelligent eyes of man.^[6] 

From Speak, Memory:

'Natural selection,' in the Darwinian sense, could not explain the miraculous coincidence of imitative aspect and imitative behaviour, nor could one appeal to the theory of 'struggle for life' when a protective device was carried to the point of mimetic subtlety, exuberance, and luxury far in excess of a predator's power of appreciation. I discovered in nature the non-utilitarian delights that I sought in art. Both were a form of magic, both were a game of intricate enchantment and deception.^[7]

Less elegantly put, Nabokov is saying that true art delights the mind because it does not serve any worldly purpose, and that this happens in nature too. To his mind, both are profoundly non-utilitarian. Nabokov had very little sympathy for what was called 'art engagé' in his times, and he did not want a 'nature engagée'. The charm of butterflies for him consisted precisely in that they – and their study – were of no practical use. He loathed the strain of Soviet entomology whose only interest in butterflies seemed to spring from the fact that some were agricultural pests that had to be fought. He cherished the thrill of "accumulation of new knowledge, absolutely useless to the layman."^[8] As the most important evidence for the non-utilitarian character of nature he cited mimicry. Mimicry usually is said to serve the purpose of protecting an animal from predators. According to Nabokov, however, it may be so staggeringly subtle and refined that it exceeds the predator's powers of discrimination.

Nabokov did not quite say that mimicry is downright useless to the mimic, though he once spoke of "the illusory theory of protective mimicry."^[9] What he said was that there is an aesthetic surplus in mimicry that the mimic has no use for and that for this reason there is more to mimicry than can be explained by its purposes. Hence it cannot have originated because of its usefulness. To say it plainly: the aesthetic surplus of mimicry falsifies the theory of evolution through natural selection.

According to the Darwinian theory evolution proceeds by the random invention of characteristics and the elimination of the useless or harmful ones. Nabokov did not reject the idea of evolution itself but the Darwinian explanation of it, and as proof of its misguidedness he used the phenomena of mimicry. In "Father's Butterflies", he came very close to postulating a creator whose intention was to amuse men by the subtlety of mimicry. This creator would on the one hand have created luxuriously mimetic animals and on the other hand the human mind for which "the unravelling of a riddle is the purest and most basic art."^[10] Thus the mind is singularly endowed to detect and appreciate the perfection of mimicry which is lost on predators. The creator would be a master artist who has not only created his work of art which is nature but also the public to enjoy it – the perceptive and discerning human mind.

Nabokov's private metaphysics obviously is in stark contrast to the prevailing opinion in contemporary science which has accepted and elaborated the Darwinian theory of evolution through natural selection as one of the most powerful theories ever devised by man and has set out to elucidate its genetic underpinnings.

Given the importance Nabokov attached to mimicry, it is surprising how few specific cases he mentions in his writings and how weak they are – weak not for the Darwinian theory of mimicry but for his dissident one. In his 1939(?) paper "Father's Butterflies" (not intended for publication and contained in Nabokov's Butterflies, 2000, p.198-234) the main purpose of which seems to be to advocate a non-utilitarian aesthetic theory of mimicry, the main brunt of the argument rests on this case:

Among the numerous illustrations of these blatant excesses of nature let us select the following example: the caterpillar of the quite local Siberian Owlet moth (»Pseudodemas tschumarae) is found exclusively on the chumara plant (Tschumara vitimensis). Its outline, its dorsal pattern, and the coloring of its fetlocks make it resemble precisely the downy, yellow, rusty-hued inflorescence of that shrub. The curious thing is that, in conformity to the rules of its family, the caterpillar appears only at summer's end, while chumara blooms only in May, so that, against the dark green of the leaves, the caterpillar, uncircled by flowers, stands out in sharp contrast ... the Siberian Owlet should by all rights have perished, having become visible to its enemy as soon as the décor changed. Instead that Owlet thrives to this day, and its caterpillar has no particular enemies.  (Father's Butterflies 222)

The first thing to note is that this case is an entirely imaginary  one. Neither the moth nor the shrub seem to exist (unless the names under which they appear here are so old that they have perished). There are just two things one can say about them: "Tschumara", otherwise spelt "Chumara", is the German spelling of a village in the Republic of Bashkortostan, Russia, about 140 km from Ufa. Vitim too is a locality in Siberia 500 km NE of Lake Baikal. So  perhaps this is where that feat of nature is happening. Demas is a real genus of holarctic noctuid moths, so "Pseudodemas" is a moth that may somehow resemble it.

Secondly, this is a case not of mimicry proper but of camouflage or crypsis: the caterpillar must be yellow, so it can hide among yellow flowers, according to the Darwinian theory of mimicry. However, as it is said to appear only when the flowers are gone, its protective coloration does not seem to serve any purpose.

If Nabokov, in the guise of Fyodor Godunov-Cherdyntsev, wanted to imagine a powerful example of mimicry disproving the Darwinian point of view, why didn't he think up something more convincing than a local yellow Siberian caterpillar whose color, if it existed in reality, could have been due to quite other reasons than the advantage of being less conspicuous? Of course, imaginary examples do not prove anything. If Nabokov resorted to an imaginary disproof of Darwinism, and such a weak one, does this imply that at the time of writing he had no forceful example for what he meant at hand? (»List of cases of mimicry in Nabokov's writings)

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It has been suggested^[11] that Nabokov's thinking on mimicry may have been influenced by the esoteric Russian philosopher Pyotr Demianovich Uspensky. There is no evidence that Nabokov ever read Uspensky. If he did, he will not have liked what he read. Still there are some obvious concurrences. In his flatly anti-Darwinian and anti-scientific treatise "Esotericism and Modern Thought" (1912–1929)^[12], Uspensky completely rejected the idea of evolution in nature, reserving the term 'evolution' for the striving of the individual spirit towards superhuman states of consciousness, something utterly alien to Nabokov. One of the reasons Uspensky gives for the falsity of Darwin's theory is the Creationist staple argument that the evolution of a new species has "never been observed anywhere." As additional disproof, Uspensky cites mimicry. The term "protective resemblance", he says, "is entirely unscientific" because it pretends to explain what so far has never been explained satisfactorily. As there are changes in color or form that make an animal similar to something else but at the same time more conspicuous to its enemies, all utilitarian theories of mimicry, says Uspensky, have to be abandoned.

Uspensky reasoned that as Darwin's theory does not allow for a (divine) plan but explains all change in nature by "accident", the accidental evolution of mimetic forms is just too improbable. For a leaf-like insect to evolve, "every green leg, the red neck, the green head with the feelers, all these, every minutest detail, every tiniest feature, must have been formed independently of all the others. In order to form an insect exactly like a leaf of the plant on which it lives, not one, but thousands, perhaps even tens of thousands, of repeated accidents would have been necessary. Those who invented 'scientific' explanations of mimicry did not take into consideration the mathematical impossibility of this kind of 'accidental' series of combinations and repetitions." In "Father's Butterflies" (which is not a scientific article but an addendum to a piece of fiction), Nabokov cautiously advanced a somewhat similar argument when he wrote that there just was not enough time for all the details of mimicry to evolve. But this is as far as the concurrence goes. Uspensky never even mentioned Nabokov's main argument against all utilitarian theories of mimicry, the subtlety that exceeds the predators' powers of discrimination. Nabokov did not need any coaching on the subject, and less still from a man whose thinking must on the whole have held little appeal for him.

Before discussing the disagreement between Nabokov and modern science, two points have to be made.

One is that at the time when Nabokov developed his refutation of natural selection, Darwinian theory was far more open to doubt and discussion than it is today. Witness Stephen Jay Gould: "… when Nabokov wrote his technical papers in the 1940s, the modern Darwinian orthodoxy had not yet congealed, and a Nabokovian style of doubt remained quite common among evolutionary biologists, particularly among taxonomists immersed in the study of anatomic detail and geographic variation …"^[13]

The other is that Nabokov's rejection of Darwinism does not vitiate neither his art nor his science. Nabokov's art has profited from an unobtrusive background of metaphysical speculation. As for science, Nabokov's job was to classify a group of small blue butterflies by close scrutiny of anatomic detail, not to philosophize on the origin of species and the world. During his years as a research fellow at the MCZ, the biological concept of the species as an interbreeding population was only slowly gaining recognition.^[14] So while Nabokov cannot be said to have been an innovator of biological theory, his dislike of Darwin's explanation of evolution did not make him a heretic or an oddball either.

Moreover, his concern with mimicry was not a poet's whim and his basic objection to the evolutionary explanation of mimicry – that it sometimes seems to exceed the predators' power of appreciation – was a scientifically sound one. Uspensky's idea that conspicuousness cannot be useful to an animal was utterly unsound and downright silly. It ignored the fact that aposematic (or warning) coloring is a widespread strategy not only in butterflies but in many animals. It serves to announce that you are noxious before the predator proceeds to sample you. By contrast, Nabokov's idea that an excess of imitative refinement would jeopardize the theory of natural selection was not at all unreasonable.

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The concept of mimicry was introduced into science by Henry Walter »Bates, faunistic explorer of the Amazon jungle. Striking superficial similarities between unrelated animals had been noted as early as the beginning of the nineteenth century, but it was Bates who systematically studied the phenomenon in longwing butterflies and put forth an explanation of how it had come about. "… some active principle must be here at work", he said in his seminal 1862 paper. "This principle can be no other than Natural Selection, the selecting agents being insectivorous animals, which gradually destroy those sports or varieties that are not sufficiently like [the mimic's model] to deceive them. ... the less perfect degrees of resemblance being, generation after generation, eliminated..."^[15] So Bates was one of the first field researchers who used Darwin's brand-new theory and came up with evidence that it was indeed correct. He sent his paper to Darwin who was enchanted. "In my opinion it is one of the most remarkable and admirable papers I ever read in my life", he wrote Bates. "The mimetic cases are truly marvellous, and you connect excellently a host of analogous facts ... You have most clearly stated and solved a wonderful problem."^[16]

Ever since mimicry has been regarded as one of the successful tests of the theory of natural selection. As the British geneticist R.A. Fisher put it in 1929, the theory of mimicry, demonstrating "the adaptive significance of the characteristics of species," is "the greatest post-Darwinian application of Natural Selection." So Nabokov was not concerned with some freakish accident of nature that was of no importance to evolutionary theory. He was aiming right at the heart of Darwinism.

Mimicry in the narrow sense, true mimicry, is the imitation of one species by another. Nabokov, just like Uspensky and many others, used the word in a wider sense, including what today is usually called crypsis or camouflage: chrysalides looking like birds' droppings, pupae looking like buds or little twigs, butterflies looking like leaves or feathers or pieces of bark and thus blending with the background. Another kind of imitation which is not true mimicry is warning in character and serves to make the animal more conspicuous to its enemies: wings with round spots that seem to imitate eyes, caterpillars looking and writhing like little snakes.

True Batesian mimicry is a subcase of aposematic (warning) patterning and coloring where one species imitates another. The model is a toxic species whose look, taste or sound the predator has learned to avoid. The mimic is an edible species that resembles the noxious one and thus enjoys the same protection. The toxic insect usually evolves a strong warning signal in order to be conspicuous and unmistakable and thus reduces the risk of dying by not being recognized. In butterflies, the warning coloration often is bright bands or spots of red, yellow, orange or black. For mimicry to evolve, the populations of the model and of the mimic must be sympatric, that is, they must inhabit the same range. Also, the Batesian mimics may not become too numerous in relation to the model, for if they did, predators would come across too many same-looking prey that are perfectly edible. In this case they would not learn to avoid them, and the protective value of the scheme would decrease. Batesian mimicry is a sort of parasitism. Only the mimic profits from it, the model has to pay for the fellow-traveler.

There is another main kind of mimicry, called Muellerian mimicry after German naturalist Fritz »Müller.^[17] Here several noxious species share the same warning pattern. They all must suffer some losses when a predator pecks at one of them for the first time, but they all profit from it, for after his first sampling he will spare them all. Muellerian mimicry is a sort of joint advertising venture by a group of animal species.

Thus the core of the theory of mimicry is that mimicry exists because it affords protection. When Nabokov voiced his disbelief, this was still nothing but a contested speculation. Beginning with a series of experiments by Jane and Lincoln Brower in the late 1950s, plenty of experimental evidence has accrued proving all assumptions of Darwinian mimicry theory right.^[18]  Yes, the noxious insects really are poisonous, mostly from feeding on poisonous plants during their caterpillar stage. For instance, the caterpillars of the Monarch (Danaus plexippus L.) feed on milkweed several kinds of which contain glycosides that in small dose make a bird vomit violently for about half an hour and in double dose would make it die of heart failure. Yes, if a bird has tasted a noxious butterfly once, it will remember the experience for a long time, probably considering its taste and its look equally disgusting. And, yes, tasty mimics are indeed protected just as well as their distasteful models. In his essay on Nabokov's lepidoptery, Stephen Jay Gould sums up the matter in just one sentence: "Nabokov's convictions on [the subject of mimicry] have not withstood the standard scientific test of time."^[19]

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Yet biology has not addressed the reason for Nabokov's rejection of mimicry theory. The reason was the aesthetic surplus that seems to be inherent in at least some cases of mimicry when resembling the model less perfectly would afford mimics just the same protection. I have not seen the subject of inferior predator discrimination discussed in the literature, but I have heard it mentioned as a potential challenge in a conference of biologists. If it were true, it would not topple evolutionary theory but it would clearly need explanation.

Does mimicry sometimes exceed the predator's power of discrimination? Nabokov did not cite any example. Indeed, it is not an established fact but a mere assumption, one that would have to be proven empirically case by case. On the face of it, it seems most unlikely when the mimic is an insect and the predator a bird. Nabokov doubted that birds are "amateurs of butterflies," but they really are. Birds also have excellent color vision, often greatly superior to that of man. Their acuity of vision may make them sensitive to very fine detail in the mimic. Nabokov wondered why a butterfly should be endowed "with the exact appearance of a certain variety of leaf with the artistic bonus of a realistic flaw: a mall hole eaten through it by somebody's larva".^[20] However, that flaw may not overtax the bird at all. If a butterfly resting with folded wings looks like a withering oakleaf as »Kallima species do, adding a few boreholes may very well add to the protection it enjoys – an improbably immaculate leaf would not blend as well with the background and be bound to raise a bird's suspicions.

Yet we simply do not know what birds or lizards or spiders see and what meaning they attach to what they see. What looks like an eye or a drop of liquid to us may look like something completely different to them. In pigeons it has been established that they do have roughly the same ideas as humans as to the mimetic perfection of hoverflies imitating wasps. The more the hoverfly looks (and buzzes) like a wasp to the human eye (and ear), the more the pigeon tends to avoid it. However, there were two exceptions in the experiment. Two hoverflies that seemed quite imperfect mimics to the human fly watcher must have seemed the most perfect ones to the pigeons for they enjoyed the greatest protection.^[21] It has been hypothesized that the reason was not the humans' but the pigeons' superiority of vision, perhaps their ability to see in the ultraviolet where man cannot see anything and where those two hoverflies may have been the most perfect of wasp mimics.^[22] 

It has also been shown experimentally that contrary to Nabokov's belief birds really are fastidious. When very hungry and confronted with nothing but a Monarch, a species they had had a nauseating experience with before, the Browers' blue-jays eyed it very closely and started to peck at it very suspiciously, first sampling those parts that usually are least offensive and to them probably tasted least vile.^[23] In short, they were behaving just as humans would. 

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Thus, while many birds would probably be able to perceive the perfection of a mimic, perfection is not a prerequisite. Actually most butterfly mimicry is far from perfect. Yet it affords protection, for usually there is no time for the bird to settle down and study its prey closely. Predation happens in real life, and in real life there is so little time and circumstances are so muddled that decisions must be taken on the basis of a quick guess and not of a thorough appreciation of the situation. The predator must act rapidly and will fare better if it generally exercises caution. If the bird sees a butterfly fluttering by in the distance that could perhaps be a Monarch, it will be better off if it flies on to look for another food item or if at least it hesitates for a moment. A predator's hesitation gives the prey a chance; the fraction of a second gained may be enough to be up and away. Any butterfly collector – that is, a person not only with with a discerning but with a knowing human mind – will admit that he too has been fooled by the tails of a resting kite swallowtail. They very poorly resemble antennae. If the collector stops to reflect that the front end of the insect is on the other side, the butterfly may be gone before he brings down his net. If he does not pause to reflect, he will be surprised to see the butterfly dart away "backwards", away from the swoosh of the net.

Richard Dawkins argues that there are many situations in which the high perceptive powers of a bird are of no avail. "No matter how good any one predator's vision may be under some conditions, it can be exceedingly poor under other conditions. […] it doesn't matter how remote, how poor is the resemblance of an insect to a stick, there must be some level of twilight, or some degree of distance away from the eye, or some degree of distraction of the predator's attention, such that even a very good eye will be fooled. [...] The point is that many an insect was saved by an exceedingly slight resemblance to a twig or a leaf or a fallen dung, on occasions when it was far away from a predator, or on occasions when the predator was looking at it at dusk, or looking at it through a fog, or looking at it while distracted by a receptive female. And many an insect was saved, perhaps from the very same predator, by an uncannily close resemblance to a twig, on occasions when the predator happened to be seeing it at relatively close range and in good light. The important thing about light intensity, distance of insect from predator, distance of image from centre of retina, and similar variables, is that they are all continuous variables. They vary by insensible degrees all the way from the extreme of invisibility to the extreme of visibility. Such continuous variables foster continuous and gradual evolution."^[24]

Evolution by natural selection is a very gradual accumulation of minimal improvements. It does not demand the protective value of some resemblance to be a hundred per cent right at the outset of the process. As long as an added feature affords some small amount of protection, it will be selected for; and if small fractions of resemblance have a chance to accumulate, they will increase the amount of protection. On the other hand, even once mimicry is perfect, there might always be predators around who are very hard to fool.

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The other objection to the evolution of mimicry by natural selection Nabokov voiced in "Father's Butterflies" perhaps unwittingly echoes Uspensky: "The impossibility of achieving false similarities via a gradual accumulation of corresponding traits, whether by chance or as a consequence of 'natural selection', is proven by a simple lack of time. […] a trillion light years would hardly be sufficient, even thanks to a series of happy coincidences, to disguise a multitude of disparate species by one and the same process."^[25]

The gradualism implicit in his theory had already worried Darwin. If evolution occurs by mutation and selection, it cannot proceed by leaps and bounds but has to very gradually add one slight change to the other. There is no big fortuitous mutation that would produce something like the eye. A complex organ must be the result of hundreds of thousands of mutations over millions of years of geological time, and each small step towards its perfection must in some way have been of advantage or else it would not have been preserved. Incredible? Darwin was able to allay his doubts. "To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree. When it was first said that the sun stood still and the world turned round, the common sense of mankind declared the doctrine false; but the old saying of Vox populi, vox Dei, as every philosopher knows, cannot be trusted in science. Reason tells me, that if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist, each grade being useful to its possessor, as is certainly the case; if further, the eye ever varies and the variations be inherited, as is likewise certainly the case and if such variations should be useful to any animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, should not be considered as subversive of the theory."^[26] 

But has there been time enough? Evolution is slow, so slow it does not usually lend itself to human observation, but it is completely  wrong to say as the Creationists do that "nobody ever saw it happen". If the selection pressure is strong and the succession of generations rapid, evolution by natural selection may be so fast than it can be watched. If you take a single Escherichia coli bacterium from the intestine, put it in a Petri dish and let it divide and multiply, there will be many millions a few hours later, forming a little pile. If you then put an antibiotic in the dish, it will kill the bacteria, and the pile will quickly dwindle and vanish. But probably not quite all the bacteria will perish. There will be two or three that will happen to have a mutation making them insensitive to the drug. They will survive, and within a few hours they will have multiplied, again forming a little pile. They are still E. coli, but with a genetic difference: they now are resistant to that very antibiotic. The deadly poison had acted as a powerful selection pressure. The altered E. coli will all be able to cope with it. And you have watched evolution happen under your eyes.

For organisms much bigger than bacteria, evolution by natural selection has been studied in the wild. Foremost are the studies of "classical" Darwin finches in the Galápagos Archipelago by Peter and Rosemary Grant. For a quarter of a century they observed and measured the morphological, behavioral and genetic changes brought about by various selection pressures – droughts, floods, the appearance of new enemies, the decline of rival species. The main lesson from the Grants' patient and exacting observations was that very small changes – less than a millimeter of beak length, for example – may indeed make all of the difference if the selection pressure is strong enough. The finches with the slightly longer beak will be able to open a certain seed and feed on it. The others will starve and die, not passing on the genes for the somewhat shorter beak. A few generations are enough to start what would develop into a new species if the selection pressures do not relax or are not reversed. It is not an exaggeration to assert that no generation is quite like the preceding one, genetically. Evolution happens all the time, and if you look close enough, you can watch it happen.

One of the best publicized instances of rapid evolution has been observed in the Lepidoptera. It has become a textbook case supporting Darwinian theory and as such a constant nuisance to Creationists. The case is that of the Peppered Moth (»Biston betularius), a Palearctic geometer moth. Its delicate pepper-and-salt pattern is subtly tuned to the bark of birch trees on which it spends the day-time. When it rests pressed flat against the tree trunk it is all but invisible. In 1848, a lepidopterist in Manchester sighted a new form (carbonarius) that was black as coal except for one white dot at the base of the forewing. Up to then, this black variant had been extremely rare, less than one per cent. Now it quickly spread from the Midlands to other parts of England and to the Continent, and within fifty years it made up 98 percent of local European populations.

Why that? Its pepper-and-salt pattern had afforded it protection from birds only as long as the birches were patterned similarly. Wherever the birches turned all black from industrial smoke, white Peppered Moths began to live conspicuously and dangerously. This was the moment of the black mutant. The Peppered Moth was not the only species in which what is called industrial melanism has been observed. Since the air has become clean and the birches white again, carbonaria is on the decline. Its incidence is down from over ninety per cent to between ten and thirty. And it does not take a great genetic change to make a white moth black. In fact, the change of color is brought about by a single mutation in just one gene.^[27]

There is no reason why it should have taken "a trillion light years" to produce a spot looking like an eye or a bore-hole on the wing of a butterfly. If the first butterfly that due to a chance mutation in its genes had a blotch on its wings – a still very botched blotch – was not eaten quite as readily as its fellows in the population, this spot was selected for, and every further incremental improvement until the eye-spot was as perfect as nature was able to make it. Evolution did not need "a trillion light years" to produce all the butterflies. Disguising them wherever useful with some semblance of an unedible object or of an unpalatable species should have taken much less time.

Today nobody believes that mimetic similarities arise by chance and at a single step through parallel mutations of the same gene in the model and the mimic as R.C. Punnett^[28] did in 1915. Nor is it likely that they come about through one single big mutation in the mimic, as Richard Goldschmidt^[29] argued in 1945. The prevailing opinion, following R.A. Fisher^[30] and E.B. Ford^[31], seems to hold that first there is a major albeit far from perfect mutant which gives a sufficiently protective resemblance to establish itself in a population and that subsequently this resemblance is incrementally improved upon by many further small step mutations.

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In any case, a butterfly's wings are not like a bitmap where each pixel – each little scale in this case – would have to be coded separately in the DNA to produce a certain pattern. They rather are like a vector image where a pattern is produced by a small number of rules. Wing patterns of butterflies seem to be made up of about a dozen discrete modules, each controlled by one gene or one gene complex. The future mimic would not have to change scale after scale until a sufficient amount of perfection is achieved. Not thousands or tens of thousands little changes would have to accrue. A few mutations in the right direction would be enough to achieve a sufficient resemblance.^[32]

I believe that Nabokov would have adjusted his ideas on the subject if he had seen the evidence coming in after he had quit his work as a research lepidopterist. His conception of evolutionary theory was still guided by nineteenth century slogans like 'struggle for life' and 'survival of the fittest' which imply a creature single-mindedly fighting, sweating and toiling for subsistence. Instead, evolution by natural and sexual selection, far from being a deploy of "unskilled forces," has itself turned out to be refined and subtle and staggeringly complex. Nature is not a Central Committee with a secret police at its service. Its purposes are utterly different from the purposes of politically minded art. The usefulness of an adaptation is not as platitudinous as Nabokov thought it must needs be. Finding, occupying and defending niches where life is possible and bringing about the necessary adaptations to exploit them efficiently takes more ingenuity than the human mind could ever muster. True, the ingenuity is not a mental one. Mutation is a random change at the genetic level, and selection is a quietly brutal elimination of the changes that do not work. Innovation thus comes about by trial and error. The method is much slower than designing a set of desirable adaptations from the start, but much safer and much more inventive. The solutions nature found to daunting survival problems are so intricate that man just barely succeeds in studying and comprehending them.

Art itself may have biological purposes of quite another order than those of littérature engagée. There is something special about the way humankind tries to achieve and to enjoy excellence for its own sake. One can imagine that a wolf hunting in a pack feels some kind of respect for the faster, stronger and more cunning individual and that this respect is not wholly made up of plain fear of the dominant pack member. Yet wolves do not hold any competitions to determine who is the best hunter and to celebrate him riotously and noisily. Because it is ubiquitous and does not have to be taught, there must be some genetic basis to humankind's universal – active and passive – appreciation of excellence. It will be long until the genes involved are sorted out, and until then one can only speculate like human ethologists did in the middle of the twentieth century.

Perhaps the evolutionary raison d'être for the special human relationship to excellence is that Homo sapiens is nature's most variable species. Talents are unequally distributed so there always is a supply of individuals who might be able to meet a new challenge. As a whole, humans are specialized in non-specialization, able to cope with the most diverse environments, from the desert to the jungle, from the pole to the equator, from the sea to the highest mountain peaks. Mankind has undergone a survival training in which the most physically fit and the most intellectually inventive individuals have been at an advantage, and everybody has profited from it. From a strictly utilitarian perspective, climbing Mt. Everest or singing the aria of the Queen of the Night is a pure waste of time and energy. The social success ("fame") that may, or may not, result from such feats is the result and not the cause of the admiration many of us are ready to feel; what we enjoy is that somebody has overcome an immense difficulty. It is useful and even essential to humankind to exercise its multiple and unequally distributed talents, even the most extreme and seemingly useless ones. Excellence and the ensuing social success improve one's sexual chances. That may be what athletics, science and art are for, biologically.

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Still, not all of evolution is utilitarian. There is evolutionary change that does not serve an immediate purpose. A mutation does not have to be advantageous to stay around. It sometimes suffices not to be disadvantageous to escape being eliminated by the perpetual test of life. If a population is split in two, for instance by a new river making its way to the sea, each part of it will accumulate its own chance mutations, and there will be no gene flow to ensure the further identity of the two populations. They will differ more and more even if the selection pressures on both stay the same. Eventually the tie will snap. If one day the river disappeared again, the two populations would not be able to interbreed. Perhaps they would not recognize each other as conspecifics any more. A reproductive barrier would keep them apart even if they became sympatric again. Evolution without a particular direction is called genetic drift.

Finally, there normally will be more than one purpose to serve. Species are shaped by contending forces, by conflicting selection pressures. The most obvious one is the conflict between natural selection, which is about survival, and sexual selection, which is about reproduction. What enhances the attractiveness to potential mates may not enhance the chances of survival. If physical fitness implies the ability to move, to run, to fly and to feed unimpeded, the male peafowl's ocellated tail or the balloon-like red gular sac of a male frigate bird are not useful but a downright nuisance to their bearers. However, they accidentally have developed as signals necessary to attract females, hence in a way they are useful after all. It is in the interest of many butterflies to be inconspicuous to their enemies and conspicuous to their mates. Many have wrought a compromise, being cryptic on the underside they show when resting on a tree trunk and brightly colored on the upperside visible only when they are in flight. It is risky for them to go looking for a chance to mate but it would be as risky to stay on the tree trunk, for if they never mated, they would not reproduce and their line would perish. The very multiplicity of purposes that have to be served demands costly and artful solutions that to the perceiving human mind may well appear artistic.  

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All of this may be useful to shed some light on a few extremely enigmatic sentences in Ada:

 Ada ... pointed out some accursed insect that had settled on an aspen trunk. (Accursed? Accursed? It was the newly described, fantastically rare vanessian, Nymphalis danaus Nab., orange-brown, with black-and-white foretips, mimicking, as its discoverer Professor Nabonidus of Babylon College, Nebraska, realized, not the Monarch butterfly directly, but the Monarch through the Viceroy, one of the Monarch's best known imitators. In Ada's angry hand.)^[33]  

Here we have one of the most famous cases of Batesian mimicry in butterflies, the Viceroy, a North American nymphalid (»Basilarchia archippus), mimicking a famous danaine, the Monarch (»Danaus plexippus), famous also among birds for its unpalatability. There also is an invented second mimic, Nymphalis danaus Nab. It is most appropriately named, Nymphalis being a real genus of nymphalids and danaus the generic name of the ultimate model. It is also appropriately rare, for the mimic must be rarer than the model. But there is something strikingly unorthodox about it. It looks like a Monarch but does not mimic it. Its model is said to be the Viceroy. The implication is that it is sympatric with the Viceroy but not with the Monarch. According to evolutionary theory, no mimicry could come about in such a case. The tasty Viceroy would afford the equally tasty danaus no protection at all. If such a case of mimicry existed, the evolutionary explanation of mimicry would have to be wrong. So Nabonidus' danaus is living proof that mimicry cannot be explained by natural selection. That's probably why Ada protests against Van's calling it accursed. If she shares her author's opinion on the matter, she would rather call it blessed.

Ironically, the history of entomology has written a footnote to this passage. In 1991, the leading authority on the biology of Monarchs, Lincoln P. Brower, discovered that the Viceroy is just as unpalatable to birds.^[34] Its caterpillar feeds on willow which does not make it poisonous but just as bitter as the Monarch. So both are disgusting, and both profit from looking alike and thus advertising their unpalatability more efficiently. The Viceroy is not the Batesian mimic it was always believed to be; both are Muellerian mimics, and perhaps all three of them are. It would be useful for the imaginary danaus to mimic the Viceroy even in the absence of the Monarch. Ada would not have to be angry when Van calls it accursed. Nabonidus' rare vanessian does not refute the evolutionary theory of mimicry at all. Rather, evolutionary theory has triumphed even over its fictional disproof.

On the other hand, Nabokov seems to have sort of pioneered this very outcome. In 1959, he told an interviewer who accompanied him on a collecting outing that he once had resorted to an unconventional experiment, putting himself in the place of a predator:

When I was younger I ate some butterflies in Vermont to see if they were poisonous. I didn't see any difference between a Monarch butterfly and a Viceroy. The taste of both was vile, but I had no ill effects. They tasted like almonds and perhaps a green cheese combination. I ate them raw. I held one in one hot little hand and one in the other. Will you eat some with me tomorrow for breakfast?^[35]