Such, then, are the colours of butterflies, and, as may be imagined, comparatively few of these gorgeous liveries have been acquired through the principle of protective resemblance—using the term in its widest sense, to include those cases where one species becomes, as it were, the double or wraith of another. Mimicry is the word which, by a ludicrous process of false reasoning, naturalists have convinced themselves it is right to apply to this particular kind of resemblance, and no other one; though why a butterfly should mimic another butterfly and only resemble a leaf, “quien sabe?” as the Spaniards say. The principal reason adduced for this misuse of language, viz. that the wrong word is more convenient than any right one, providing us with the useful series, mimic, mimicry, mimetic, mimicker, mimicked, mimicking, obviously applies to the one case as well as the other, and if it is an advantage to be absurd in one way, surely it is a double one to be absurd in two. On these grounds I would suggest to naturalists that, having broken down the proper and natural confinements of the word in question, they should rather extend its use than limit it, to the extent even of calling their children “mimetic forms,” should they happen to resemble them, and thinking twice before punishing a son for merely “mimicking” his father.
But, leaving this, how—to take the jargon as one finds it—are the glorious colours of butterflies to be explained when they are due neither to protective resemblance, which is not mimicry, though it very much resembles it, nor to mimicry, which is distinct from protective resemblance, though mimicking it exactly? Certainly neither of these will do to account for uncopied hues and patterns, which are like nothing in the world but their own loveliness, unless, indeed, it be the rival glories of the most resplendent birds. Still less will aggressive resemblance—though, as we see, it can make spiders look like flowers—explain them. The great governing cause which produces such effects as these, as well as most others in nature, is natural selection; but we must look beyond natural selection even, if we wish to understand all the beauty that we see in the animal world, and especially the higher developments of it.
Darwin, as we know, was the great demonstrator—though not the first conceiver—of the law of natural selection,[[118]] and on this he might have cried “Nunc dimittis” and retired, so to speak, leaving someone else to find out the other law; but instead of that he went on and demonstrated that too. This other law, the evidence for which is really overwhelming, and has never been met by anything better than a conceited over-estimation of human superiority, wrapped up in a cloud of wrong reasoning, is that of sexual selection, which implies that, in the choice of their mates, animals, like ourselves, are guided by some sort of preference; and as this with them—again like ourselves—is usually determined by the element of beauty, the most beautiful partners are being constantly selected, and species in consequence become more and more beautiful. This process, however, is usually confined to the males, they being the eager wooers, whilst the females only wait to be courted, and then shyly and modestly choose—such, at least, is the supposition. This masculine beauty is often inherited by that sex only to which it is so useful, but in other cases it is transmitted to the female also. Thus, to take birds, where the results of the law of sexual selection are on the whole most pronounced, we have, on the one hand, the pheasants and birds of paradise, where the male alone is resplendent, whilst in the trogons, parrots, and many other species the beauty is common to both the sexes. As is well known, the males of various highly ornate birds are accustomed to make the most extraordinary display of their beauty before the females, making the most of the parts most richly decorated, assuming just such attitudes as are required in order to give these their full advantage, and, in fact, taking pains and trouble in a high degree and of a very special and peculiar kind, which must either be directed to an end which seems perfectly plain and apparent, or else so much waste of time—due to no special cause and without any particular meaning—an alternative which the opponents of sexual selection do not in the least mind accepting.
To give one instance of what is called nuptial display in birds—for it will serve to illustrate what Darwin supposes to take place with some insects also, as well as forming a basis of comparison with what has been more carefully observed in the case of spiders—Belt in his often quoted work gives us the following pretty picture of humming-bird courtship. Speaking of a beautiful blue, green, and white species (Florisuga mellivora), he says: “I have seen the female sitting quietly on a branch, and two males displaying their charms in front of her. One would shoot up like a rocket, then suddenly expanding the snow-white tail like an inverted parachute, slowly descend in front of her, turning round gradually to show off both back and front. The effect was heightened by the wings being invisible from a distance of a few yards, both from their great velocity of movement and from not having the metallic lustre of the rest of the body. The expanded white tail covered more space than all the rest of the bird, and was evidently the grand feature in the performance. Whilst one was descending, the other would shoot up and come slowly down expanded. The entertainment would end in a fight between the two performers; but whether the most beautiful or the most pugnacious was the accepted suitor I know not.”[[119]]
Here the display, as well as the intention, seems evident enough, and it is not a whit more so than in hundreds of other cases collected by Darwin during his lifetime, and which have been largely added to since his death. As the hen is constantly present during these performances, and as she has been known on various occasions to show a strong partiality, or the reverse, to this or that male bird, we have here a solid basis of observed fact on which to raise an hypothesis. On what facts the counter one rests, as propounded by Dr. Wallace, viz. that colour and antics are produced by superior vigour resident in the male, it is less easy to see, unless, indeed, such as point in a quite opposite direction may, on a sort of lucus a non lucendo principle, be held to support it. If this be conceded, then, indeed, we have a plentiful crop, nor need we any longer feel sceptical because the eagle, say—that bird of fierce energy—does not flash out like all the crown jewels together as it descends on its prey, or because the swift, whose vital force is, perhaps, even greater, leaves no train of jewelled light to die all day, behind it, on the air. Nor need we wonder that the trogons, though as resplendent as the swifts, swallows[[120]] and eagles are dull-coloured, should be as lazy and sluggish as these are energetic: nor that, whereas the females of some humming-birds are sober-suited, those of others, though their vigour would seem to be in no way superior, are as gem-like as their mates: or that the males as well as the females of some wholly dull-coloured ones, and of many other plain birds, seem bursting with vigour, and indulge in all sorts of strange antics and dances: that a cock partridge, for instance, seems as vigorous as a cock pheasant, and that bright colours and pugnacity are dissociated in such tremendous fighters as the ruff, the coot, and the blackcock. Multiply such instances by the score or the hundred—as can easily be done—and if only the above-stated principle be granted, we get more and more proof of the correctness of a theory to which facts, if dealt with in the more usual way, would be almost instantly fatal. After all, this would be a more satisfactory mode of procedure than that of tolerating a travesty on the strength of a high reputation. There is such a principle in nature as the lucus a non lucendo one, so, as we admit the word mimicry in a false sense—because it is convenient—why not admit that? It would be not one whit less convenient—for the theory.
But, handling facts in another way, can we explain the beautiful colours of butterflies as we explain the brilliant plumage of birds—by sexual selection, that is to say? Of this there is not so much direct evidence as could be wished, for butterfly courtship is a long affair, and, for various reasons, is not so easy to watch under natural conditions, as in the case of birds, though this, too, is often beset with difficulties. We know, however, that the male is often much more beautiful than the female, that he pirouettes around her, and that she remains often “icy insensible”—in fact refuses him—which certainly implies a power of choice. Rival males, too, will “whirl round each other with the greatest rapidity, and appear to be incited by the greatest ferocity.”[[121]] That butterflies, like bees, perceive and are attracted by colours is well known, and it would be strange, indeed, if they were not alive to the many very beautiful and complex patterns on their own wings, when these cannot have been evolved through any principle of protection—since they resemble or suggest nothing—when, in fact, if not beauty, it is difficult to see the object aimed at. Yet the strange suggestion has been made that, though butterflies see colours, they cannot see form, that their sight is defective in some peculiar kind of way. But if form is outline—and if not, what is it?—where is the distinction, seeing that the beginning and leaving off of a colour or of two or more colours must make an outline, and therefore a form? If we see the colours of a pattern where the one ends and the other begins, we see that pattern, and on the other hand, if we could not distinguish one colour from another, or colour from something uncoloured—as, say, the air—we should be blind to colour, as well as to form. Form can hardly be called a thing of itself. It is rather the line of demarcation between two or more things, so that, if each of these is clearly perceived, the form or outline which their juxtaposition makes must be also perceived. Assuming that butterflies see the beautiful arrangements of colour—eyes, spots, bands, lines, etc.—in such a way as can alone account for their being there to see—as well as we do, that is to say—then it is absurd to imagine that they have no perception of form.
On what is this assertion based? Mr. Scudder relies on the following facts: “Christy,” he tells us, “observed in Manitoba one of the swallow-tails fluttering over the bushes, evidently in search of flowers. As he watched it, it settled momentarily, and exactly as if it had mistaken it for a yellow flower, on a twig of Betula glandulosa, bearing withered leaves of a bright yellow colour.”[[122]] But might not the association of ideas raised by a familiar colour in an insect’s mind overpower for a moment its judgment? Might it not do so in the case of a man also? And should we think a person very stupid who, for a moment, mistaking a yellow leaf for a yellow flower, stretched out his hand to pick it? Pooh! once again,[[123]] let us think of people who do foolish things—kings, generals, cabinet ministers, servant-maids, etc.—not of infallible persons. We should not be too severe—not “break a butterfly on a wheel.”
Again—this is Mr. Scudder’s second instance: “Albert Müller records seeing the blue Alexis of Europe fly towards a very small bit of pale blue paper lying upon the grass, and stop within an inch or two of it, as if to settle, doubtless mistaking it for another of its own kind.”[[124]] Surely this is rather in favour of the butterfly’s sight than otherwise, since it discovered its mistake and did not settle. Who, too, can tell the precise moment at which the mistake was discovered, since the piece of blue paper might have puzzled the butterfly—piqued its curiosity to know what it was—even after it knew what it was not? Thirdly, “Plateau has observed the small tortoise-shell butterfly fly rapidly towards a cluster of artificial flowers.”[[124]] And who cannot be taken in by artificial flowers? “Such examples as these,” says Mr. Scudder, “seem to indicate that butterflies may perceive colour in mass, but in no case indicate any further visual powers.”[[124]] To me they indicate that butterflies can make mistakes. Mistakes rarely show one’s perfections, but other indications of further visual powers are not wanting. For instance, Mr. Scudder himself says: “One of my favourite modes of showing this characteristic (inquisitiveness) to unbelieving friends has been to toss my cap high in the air, when these butterflies will often dart, dash at, and play around it as it begins again to descend.”[[124]] How do they play around this moving object in the air if it represents to them only “colour in mass,” and not a defined shape and outline? Were it otherwise, they would fly right into it, and be carried down with it sometimes on top of them. But if they see all parts of the colour so that they can nicely avoid it, and sport about its periphery, then they see the shape of the cap. Then, again, Mr. Scudder tells us: “Many kinds are of a lively and even pugnacious disposition, and perch themselves upon the tip of a twig, or on a stone, or some such outlook, and dash at the first butterfly that passes, especially if it be one of their own species;[[125]] then the two advance and retreat, forwards and backwards, time and again, circle round each other with amazing celerity, all the while, perchance, mounting skywards, until suddenly they part, dash to the ground, and the now quiet pursuer again stations himself on the very spot he quitted for the fray.”[[126]] How does he do that without accurate eyesight, with good defining power?—to which, indeed, the whole performance bears witness. Elsewhere, too, this pronounced characteristic of returning to the exact spot, left some little time ago, is dwelt upon. To me it seems a complete upsettal of the defective eyesight theory, or, since good eyesight could do no more, what does such defectiveness matter?
The following description also, which Bates gives us, of butterfly-life by the Amazons, does not suggest that any of these bright-day-lovers, these children of the sun, need write an “Apologia pro oculis suis.” “The fine showy Heliconii,” he says, “often assemble in small parties, or by twos and threes, apparently to sport together or perform a kind of dance” (my “dancing in the chequered shade,” therefore, was no inapt quotation). “I believe the parties are composed chiefly of males. The sport begins generally between a single pair. They advance, retire, glide right and left in face of each other, wheel round to a considerable distance, again approach, and so on; a third joins in, then a fourth, or more. They never touch;[[127]] when too many are congregated a general flutter takes place, and they all fly off, to fall in again by pairs shortly afterwards.”[[128]] Lastly, Belt tells us this: “Here a large spider built strong, yellow, silken webs joined one on to the other, so as to make a complete curtain of web, in which were entangled many large butterflies, generally forest species, caught when flying across the clearing. I was at first surprised to find that the kinds that frequent open places were not caught, although they abounded on low white-flowered shrubs close to the webs; but on getting behind them and trying to frighten them within the silken curtain, their instinct taught them to avoid it, for, although startled, they threaded their way through open spaces and between the webs with the greatest ease.”[[129]] If a butterfly with defective eyesight can thread its way between spiders’ webs, so as never to be caught, “with the greatest ease,” “why, then, say an old man can do somewhat”—but it must be without spectacles.