Popular Science Monthly/Volume 72/April 1908/Accidental Resemblances Among Animals - Chapter in Un-Natural History
|ACCIDENTAL RESEMBLANCES AMONG ANIMALS. A CHAPTER IN UN-NATURAL HISTORY|
By Professor BASHFORD DEAN
THE naturalist of to-day is perhaps unduly saturated with the belief that animals and plants adapt themselves to their surroundings. He has seen so many and such admirable examples of this, and in every field of his work, that he is apt to conclude that the principle of adaptation can be called upon to explain phenomena which when critically considered may prove to be not adaptive at all. In the familiar case of an insect whose colors suggest lichen-covered bark, or a dead leaf, or a flower, we have come to conclude, since we have seen many examples of demonstrated utility, that the resemblance is significant, that it protects the insect against its enemies and that it has been the outcome of a series of evolutional changes which have made the protective coloration more and more complete. We have even reached a point, some of us at least, where we neglect to scrutinize the evidence that the creature in question frequented the kind of bark, leaf or flower which it resembles, or that, if it did, it was thereby protected so completely as to ensure its survival. We have reached the point, to make this attitude clear, when we hold up before our students a butterfly mounted on a twig and point out the marvelous "protective" resemblance between the butterfly and the neighboring pressed leaves, without suspecting that the leaves belonged to a beech tree "made in Germany," and that the butterfly came from the East Indies!
So also is our attitude a lax one in the case of animals which resemble other animals and are thereby protected, like moths which resemble wasps, flies which can be mistaken for bees, butterflies which are similar to butterflies known to be rejected by birds, etc. For we have seen so many instances of undoubted mimicry that we are apt to accept resemblances as of this type, even if they have not been experimentally demonstrated. That such accurate resemblances, on the other hand, could occur even in animals which live side by side and yet mean nothing, would be something of a heresy to many evolutionists. Yet I am inclined to believe that this is a fact—although to prove this in concrete instances would be at the moment difficult. However, it can, I think, be established indirectly and by striking analogies. For if there occur among animals numerous resemblances which mean nothing, we may justly be skeptical of other resemblances—unless their value can be experimentally proven. In point of fact, if we sift out the cases in which mimicry and protective coloration have been demonstrated beyond question, we find that their number is by no means as large as we at first assume. And of the remaining cases, probable, or imperfectly proven, we should, in fairness, leave open the possibility that what seems protectively colored or mimetic resemblance might in the end turn out to be accidental and meaningless. And in the present notice it may be interesting to refer to these meaningless resemblances in order to show both that they are abundant, and that they are excessively complicated—in certain cases, even more complicated than those which are commonly regarded as typical, if not brilliant instances of protective or mimetic adaptation.
As an example of a meaningless resemblance let us first refer to the Taira-crab, a Dorippe, Fig. 1, on whose back a human face appears strikingly portrayed. This crab occurs rather abundantly in a region of the Japanese coast where many centuries ago a great naval battle took place: and it was only after this time, local Buddhistic tradition states, that a face of a Taira warrior appeared on each carapace, as tangible evidence that the souls of the dead migrated into the bodies of these lower animals! Now, the resemblance in this case is developed to an almost uncanny degree; the face, first of all, is clearly oriental—even more Chinese or Corean in type than modern Japanese, but from this very fact the more singular, since at that time but few Ainos had been absorbed into the Japanese race, and its physical features were therefore, on historical evidence, more strongly continental. The face, in the second place, is that of a drowned man: it is horridly infiltrated, the nose swollen and the mouth widely opened. In such a case the complicated nature of the meaningless resemblance can hardly be overestimated. For we have in it, as will be seen, a series of resemblances which are added one to the other, from the general to the specific, in somewhat the following way: human face (in itself, of course, a very complicated structure): male: young: oriental: primitive Japanese: drowned.
A second meaningless resemblance is shown, Fig. 2, in a whale's "earbone" which was found on a beach in Norway: it portrays in half relief a Scandinavian face of low caste, and with almost absurd accuracy—with rounded cheek-bones, flattened nose-bridge, small upper lip and receding jaw.
In both of these cases there is an extraordinary meaningless correspondence between the resembling objects and the especial locality in which they occur. And this condition occurs with amusing frequency.
A case in point occurs in the skull of a goat, Fig. 3, picked up in Agra, which shows on its supra-occiput the face of the common monkey of the locality, the Hanuman (Presbytes entellus), for it shows (with a slight tax on the imagination) the front view of this monkey's forwardly directed beard, cheek-tufts and brow-hair, and these, too, in light tone against the dark-colored face.
Another possible case is that of the squash seeds, Fig. 4, which in drying acquire irregular depressions on their surface, and thus produce
the effect of idiographs. They are said to have come originally from Japan, but in any event so perfect are the "characters" that I have known a Japanese scholar to puzzle over them for several minutes in his effort to read them!
A somewhat analogous instance, Japanese (noted by my friend, Dr. Yatsu), is that of the "Tokugawa fish," a small species of Salanx, which is said to have appeared in Yedo (Tokyo) shortly after the last dynasty of regents made their seat there. This fish is curious in that its head bears the badge of the Tokugawa family, the three Asarum leaves conjoined. This effect is produced by the lobes of the brain, which can be clearly seen through the transparent headroof.
An example which pictures a human face almost as strikingly as in the Taira crab is seen in the chrysalis of the butterfly, Feniseca tarquinius, Fig. 5. For here the resemblance is developed in remarkable
Fig. 5. Pupa of the Butterfly, Feniseca tarquineus. (Cut loaned from Entomological News, through the kindness of its editor, Dr. Skinner.)
detail, with forehead wrinkles, eyebrows and lids, aquiline nose, thin determined lips and straight mouth—all in this case as palpably Caucasian as the Taira face was proto-Japanese. If the present photograph had been taken from a larial mask of Tarquin himself, it could hardly appear more human!
A second pupa-portrait is given in Fig. 6, in the case of Spalgis S-signata Hol. In this instance not only are the characters of Feniseca paralleled, but there appear hair (frankly not a vast chevalure) on the "head," pupil in the "eyes," and the general appearance in grotesque of the head of a chimpanzee. Not remarkable, therefore, that the habitat of the "mimicking" insect is West Africa!
A third pupa portrait, Fig. 7, again a Feniseca, but I do not know of what species, is taken from a photograph of a dried specimen. It has the face-like appearance, and suggests amusingly the restoration of the Brontosaurus, in the American Museum.
Still another meaningless resemblance is in the death's head moth, Acherontia atropos, which shows a "remarkably faithful delineation of a skull and bones upon the back of the thorax." And in allied species the skull is even more sharply pictured—in A. lachesis, for example, where it appears insize.
A less familiar case, and as obviously meaningless, is the resemblance to a cuttle fish, which one finds in the end view of the larva of the crane-fly, Tipula abdominalis, Fig. 8. This appearance might conceivably inspire a wholesome dread among some marine creatures—but the fact remains that the present larva lives in wet rotten wood (or under ground) where an octopus-like resemblance could not benefit it. Indeed among insects one may find numerous instances of accidental resemblances. Some pupæ we have already referred to. Others, bombycids, for example, suggest mummy cases, the region of wings, antennæ and tongue, picturing both in form and proportions the Egyptian head-gear and beard. It is improbable, to say the least, that the Egyptians arrayed their dead after the fashion of a pupa to encourage a teleological analogy, for one reason, since the headdress and beard were displayed in a similar fashion during the lifetime of the individual. Striking, too, are pictures which one sometimes finds on the wings of butterflies—among these, as Mr. Beutenmüller showed me, are the heads of French poodles, which appear en silhouette on the wings of the orange colored butterfly, Colias (cæsonia and eurydice). And on the hind wings of the ragged butterflies (Grapta), as every one knows, appear commas and semicolons printed in silver upon an otherwise dull colored wing. In the group of bugs (Hemiptera) one recalls the initial W, which occurs in certain cicadas, and there is the interesting case of the tree-hopper, Membracis binolata. to which Professor Wheeler drew my attention. This tree-hopper and its young represent amazingly "a family of tiny birds with long necks and swelling breasts and dropping tails, verily like an autumn brood of bob-whites" (W. H. Gibson), Fig. 9. Had they been twenty times their present size they might have run the risk of being described as mimics!
Among other resemblances of this nature one recalls the spectacles which appear on the neck of the cobra. Then there are the insect,
Fig. 8. "Octopus" shown in hindmost abdominal Segments of the larval Tipula.
monkey and human figures in orchids and in various other plants, pictured in flowers, parts of flowers and in fruit. The last sometimes give striking and grotesque forms, as in the case of our common garden snap-dragon, Antirrhinum. Here, Fig. 10, the seed pods look like diminutive human heads which are arranged on the stalk in a way which suggests the poles-of-skulls, or "medicine" ornaments of certain savages. Peculiarly perfect is this resemblance, for there are pictured not merely the cranium and face, but the dried and weathered portions of scalp, eyelids, lips, as well also as temporal sutures. The color of these seed pods, furthermore, is strikingly like that of mummied heads. Meaningless resemblances occur also in various bones, as in the case of the goat skull or the "ear-bone" noted above. Thus, as Hugh Miller long ago discovered, there is a curious human figure in the cranium of a Devonian fish, and the rabbit, even when "dead and turned to dust" is not free from its arch-enemy, for its sphenoid (Fig. 6) pictures the head of a fox so cunningly indeed that this bone has long been used as a scarf ornament for the English hunter.
Instances of this kind need hardly be multiplied. They extend on every side in the inorganic as well as the organic—from the simple cloud figures conjured by Aristophanes or the various forms of weathered rocks (like the "camel of Brignogan"), to the most curious and complicated. In short, therefore, it is clear that if meaningless resemblances are numerous and striking, one can accept protective resemblance and mimicry only in instances which have been fully demonstrated. And we may in the meanwhile mark as doubtful numerous cases which now pass current in zoological literature. Among these would, I believe, fall the famous leaf-like butterfly, Kallima, which Weismann has adopted as the ne plus ultra of protective resemblance, for in the lack of adequate experimental evidence even this form may prove to be a meaningless resemblance, and not the product of selection. That it may be, and probably is, of protective value at the present time can as readily follow from an accidental resemblance which happens to turn out to be valuable as from one which has been the product of
Fig. 9. Tree-hoppers whose appearance suggests birds. After Gibson in Century.
(Cut kindly loaned by Dr. Skinner.)
numberless selected variations. In fact, it is quite credible, it seems to me, that accidental favorable variation may have furnished the basis of many a useful resemblance—as some mutationists believe. And there are no peculiar "adaptive characters" in Kallima which can safely be construed as more complicated than the meaningless characters of the Taira crab. For in what way is the resemblance of a butterfly with folded wings to a leaf more remarkable than the appearance of a human face on the back of a crab? For the contrast, when dissected, would give us in the one case the characters—leaf-shape, color, midrib, reversed markings (veins) on one side of midrib, concealed legs and antennæ, "petiole," and fungus-like patches, as opposed, in the case of the crab, to the equally complicated characters—human face, color, young, oriental, primitive Japanese, drowned. It is only fair to conclude, therefore, that if a meaningless variation can produce the Taira crab, it might equally well have produced Kallima. The conclusion, indeed, that Kallima formed the apex of a series of selected changes, is, on our present evidence as to the habits of this insect, hardly different in kind from the assumption that the present perfection of the skull on the death's head moth is the result of selective
changes, through whose agency this form came gradually to be avoided and thus secured immunity from, by superstitious man, an important enemy! In fact, in this case, there is actually a stronger body of evidence that the moth is avoided by man than that Kallima is overlooked by birds.
In a word, it is a fair conclusion that our notions of protective resemblance and mimicry are carried in numerous instances farther than the law allows. And one does not have to go far afield for cases in point. Thus-the snake's head which is pictured on the wing tip of an East Indian moth, Attacus atlas, does not strike one as a convincing ease of mimicry, in spite of Weismann's arguments. It is true that the snake is strikingly portrayed, both in color, poise and expression, and we will readily admit that it might give a wholesome jolt to some enemy of the moth which happened to see it just at the right angle. But the picture in this instance is not more striking than many of the meaningless resemblances we have quoted (e. g., the French poodle pictured on the wing of Colias), and I think we may reasonably demand definite experimental proof before accepting the "mimicry." In certain other instances one can not feel assured that the resemblance is of actual value to the "protected" form. As an instance of this, I recall the living Icthyophis, the curious burrowing salamander, which I once had the opportunity of observing in Ceylon. This is surprisingly like a worm in many regards, yet a mimic it can not be, since it could derive no profit from the resemblance, the worm being infinitely less protected than itself. If any mimicry could exist in this case it is clearly in the opposite direction, the worm mimicking the salamander, but this possibility is precluded since the mimicking form is infinitely more plentiful than the mimicked, and, most significant, neither form is apt to expose itself in a light where the resemblance would have any value. None the less the mutual resemblance is quite striking—in shape, proportions, size, color, annulation, movements, position of vent, etc. Yet we can only interpret it as due to parallelism. And if this is the case, may not parallelism, i. e., similarity in structures due to similarity in habits, not mere accidental resemblance, be taken as a further danger in interpretation.
For the rest we may query, as others have done, whether the importance of protective coloration and mimicry may not be still further diminished when we eliminate our anthropomorphic conception of the senses of the lower animals. For we may reasonably harbor the suspicion that colors and patterns, which to man seem protective, are by no means as valuable as protection against the keener and more specialized visual impressions of the lower animals. For just as "scent" perception in certain invertebrates, as in various moths, is immeasurably refined, far more so than we are in the habit of conceiving the scent-sense, so also there may have been developed a special sense for detecting the most subtle differences in color, texture, form in those animals which prey upon mimetic and protectively colored forms. Indeed, such a view is the less unreasonable when one considers the condition of the optic centers and end organs in those vertebrates, teleosts, reptiles, amphibia, birds, which have most to do with creatures in which protective coloration and mimicry is supposed to occur most abundantly. And it is not beyond the pale of possibility that the predatory forms have evolved habits in connection with sense-organs which would cause them to distinguish more promptly the protected forms than those having bright and obvious colors. It is in this direction that we have need of close observation and critical experiment.
- A.D. 1184, at Dan-no-ura, the Taira clan was exterminated by the rival Minamoto headed by Prince Yoshitsuné.
- For the permission to use this figure, and the loan of the cut itself, we are greatly indebted to Dr. Skinner, the editor of the Entomological News.
- For this I am indebted to Professor Wheeler.
- In this connection, cf. a note in Science, Vol. XVI., p. 832, in which the present writer comments upon the scantiness of evidence as to the protective value of the characters of Kallima, and notes the appearance of this insect on and near leaves which it in no way resembled.