Mimicry (biology)

“ On the theory of mimicry all the members of both of these groups must be regarded as specially protected owing to their conspicuous coloration and distasteful properties. What advantage then can an Ithomiine be supposed to gain by mimicking a Heliconine, or vice versâ? Why should a species exchange its own bright and conspicuous warning pattern for one which is neither brighter nor more conspicuous? ”

“ Briefly defined, the phenomenon of mimicry is that relation which obtains when “a certain species of plants or animal possesses some special means of defense from its enemies and some other species inhabiting the same district or a part of it, and not itself provided with the same special means of defense, closely resembles the first species in all external points of form and color, though often very different in structure and unrelated in the biological order.” ”

“ The former process would be a true instance of "active mimicry," as defined by Mr. Distant, but the latter cannot be included under that term; indeed, in such cases, experience in the individual is the equivalent of natural selection in the species.
In the preliminary portion of his paper, Mr. Distant has given us many excellent examples and arguments to show that mimicry and protective resemblance probably existed in very remote antiquity; (n10) and he has done well in drawing attention to the matter, which is apt to be overlooked. ”

“ The truth will not penetrate a preoccupied mind." (To Sir J. Hooker, July 28, 1868, "More Letters", I. page 305. See also the letter to A.R. Wallace, April 30, 1868, in "More Letters" II. page 77, lines 6-8 from top.)
There are many naturalists, especially students of insects, who appear to entertain an inveterate hostility to any theory of mimicry. Some of them are eager investigators in the fascinating field of geographical distribution, so essential for the study of Mimicry itself. ”

“ Having reviewed briefly some of the most striking phenomena of what has been termed mimicry, we may now inquire whether there are good grounds for supposing that these resemblances have been brought about through the operation of natural selection or whether they are due to some other cause. If we propose to offer an explanation in terms of natural selection we are thereby committed to the view that these resemblances are of the nature of adaptation. For unless we grant this we cannot suppose that natural selection has had anything to do either with their origin or with their survival. ”

“ But, what is more important, mimicry and resemblance are only particular aspects of the principle of natural selection, and therefore if the factors of mimicry do not exist to-day, then, a posteriori, neither do those of natural selection. A single glance at nature is sufficient to justify the rejection of such a conclusion, and we must, therefore, admit that the factors of mimicry are in actual operation now ”

“ What is important from the standpoint of mimicry is that these divisions, made solely on anatomical structure, correspond closely with the separation of models from mimics. Of the eight sub-families into which the Nymphalidae are divided four, viz. the Danainae, Acraeinae, Heliconinae, and Ithomiinae, provide models and some, but far fewer, mimics; two, the Satyrinae and Nymphalinae, provide many mimics and but few models, while two groups, the Morphinae and Brassolinae, practically do not enter into the mimicry story. ”

“ It must, of course, be understood that the mimicry is unconscious, the result, as in the cases of cryptic resemblance, having been brought about by natural selection—the less perfect the mimicry the more liable are the individuals to be attacked, and the less chance have they of reproducing their kind. ”

“ And it must be added that while this fact of mimicry is of extraordinarily frequent occurrence, there can be no possibility of our mistaking its purpose. For the fact is never observable except in the case of species which occupy the same area or district.
Fig. 114.—Two further cases of mimicry; flies resembling a wasp in the one and a bee in the other. Drawn from nature: nat. ”

“ Although, like protective resemblance, quite independent of affinity between the organisms concerned in the likeness, mimicry occurs most commonly between animals structurally similar, and therefore related, to one another, the relationship may be close or remote. For instance, the commonest and best-known cases are found in insects where both mimic and model may belong to the same genus, sub-family, family or order, or to different orders. More rarely it occurs between members of distinct classes of the same sub-kingdom, i.e. between spiders and ants or spiders and beetles ”

“ It does not bring about the likeness, neither does it accentuate it: it brings about the survival of those forms which happen to shew the likeness. Why variations on the part of one species should bear a strong resemblance to other, and often distantly related, species is another question altogether.
Even a superficial survey of the facts makes it evident that cases of mimicry tend to run in series—that a closely related series of mimics, though often of very different pattern and colour, tends to resemble a closely related series of models. ”

“ Newton maintains that mimicry must have the prefix "unconscious," "which in every department of Zoology should be always expressed or understood"; and, again, wherever mimicry is not only possible, but even probable, "we must always remember that however produced it is unconscious." ”

“ When we further realize that in this and other examples of mimicry “the likeness is almost always detailed and remarkable, however it is attained, while the methods differ absolutely,” we recognize that natural selection is the only possible explanation hitherto suggested. In the cases of aggressive mimicry an animal resembles some object which is attractive to its prey. Examples are found in the flower-like species of Mantis, which attract the insects on which they feed. ”

“ Recent botanical and entomological researches have made Science familiar with what is termed Mimicry. Certain organisms in one Kingdom assume, for purposes of their own, the outward form of organisms belonging to another. This curious hypocrisy is practiced both by plants and animals, the object being to secure some personal advantage, usually safety, which would be denied were the organism always to play its part in Nature in propria persona. ”

“ Mimicry is a special branch of the study of adaptation. The term has sometimes been used loosely to include cases where an animal, most frequently an insect, bears a strong and often most remarkable resemblance to some feature of its inanimate surroundings. Many butterflies with wings closed are wonderfully like dead leaves ”

“ Such is the first step in the making of a mimicry case—the building up through natural selection of a conspicuous pattern in an unpalatable species by means of which it is enabled to advertise its disagreeable properties effectively and thereby secure immunity from the attacks of enemies which are able to appreciate the advertisement. Such patterns and colours are said to be of a "warning" nature. The existence of an unpalatable model in considerable numbers is the first step in the production of a mimetic resemblance through the agency of natural selection. ”

“ In conclusion, I can only hope that sufficient has been said to show that there are good grounds for opposing the suggestion that active mimicry is of any general occurrence in the animal kingdom; and, further, that the attempt to minimise certain phenomena of ordinary protective resemblance, in order to bring them within the scope of that principle, is not justifiable upon the evidence adduced. ”

“ If, however, the mimetic resemblance is not fully established and the mimic bears only what supporters of the mimicry theory term a "rough" resemblance to the model, it is clear that it will have far less chance of being mistaken for the model. ”

“ If so natural selection may have favoured the new variety, not because of its colour scheme, but owing to the underlying physiological differences of which the pattern is but an outward sign. And if this could happen in one species there seems to be no reason why it should not happen in others. The weak point of the explanation on the mimicry hypothesis is that it offers no explanation of the change in the so-called dominant Ithomiine pattern as we pass from one region to another. ”

“ Palm trees, like human beings, are male and female. The garden plants, the date bearers, were females; the desert plants were males; and the waving of the branches over the females meant the transference of the fertilizing pollen dust from the one to the other." [54]
The time has arrived when the whole theory of "protective resemblance" and (or) "mimicry" [55] requires to be expressed and understood in two senses, viz. Demonstrated, and Suggested or Probable. I propose also to give instances of what may be considered as Disputed or Mistaken Mimicry, and likewise Purposeless Mimicry. ”

“ There is a distinct family resemblance among the bulk of the Dismorphias, including practically all the mimetic forms, and on the whole the resemblances between the imitative and the non-imitative forms are as noteworthy as the differences. Though not exhibited in so striking a fashion, the same is to a large extent true of a large proportion of the cases of mimicry. It is on the whole unusual to find cases where a single species departs widely from the pattern scheme of the other members of the genus and at the same time resembles an unrelated species. ”

“ An important phenomenon connected with insect mimicry is the convergence of several species in the same area towards a common type of coloration and shape, exhibited by one or more than one protected form. The resemblance shows various grades of completeness; and the convergent mimics may be themselves noxious, or edible and innocuous. In other words the insects entering into the combination may furnish instances of Batesian and of Müllerian mimicry. ”

“ The theory of mimicry demands that butterflies should have enemies, and further that those enemies should exercise a certain discrimination in their attacks. They must be sufficiently observant to notice the difference between the mimetic and the non-mimetic form ”

“ 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 ”

“ It is this, that while, among various kinds of animals, it is possible to discover traces of all the other faculties of man, especially the faculty of mimicry, yet that particular form of mimicry which shows itself in the imitation of form, either by modelling or by drawing, is not to be met with. ”

“ The most obvious is, that we have gradations of mimicry and of protective resemblance—a fact which is strongly suggestive of a natural process having been at work. Another very serious objection is, that as mimicry has been shown to be useful only to those species and groups which [109] are rare and probably dying out, and would cease to have any effect should the proportionate abundance of the two species be reversed, it follows that on the special-creation theory the one species must have been created plentiful, the other rare ”

“ We can only report that these insects are mimics one of another as seen in our cabinets, and that as nothing is, or can be, predicated as purposeless in nature, neither can these assimilative forms be meaningless; and, further, arguing from demonstrated knowledge in other cases of mimicry being protective, the presumptive evidence is that the theory of protection affords the clue to the origin of the mimetic guise of these insects. ”

“ Though "mimicry" is but a small corner in this vast field of inquiry it is a peculiarly favourable one owing to the great interest which it has excited for many years and the consequently considerable store of facts that has been accumulated. ”

“ There are writers on these questions of mimicry who adopt a view more or less intermediate between those just discussed. They regard the resemblance as having arisen in the first place as a sport of some magnitude on the part of the mimic, rendering it sufficiently like the model to cause some confusion between the two. A rough-hewn resemblance is first brought about by a process of mutation. Natural selection is in this way given something to work on, and forthwith proceeds to polish up the resemblance until it becomes exceedingly close. ”

“ The larger the mimetic company is the greater will be the protection afforded to its palatable mimics, since they will be the more rarely seized by way of experiment. It is, of course, obvious that in this kind of mimicry—that is, in the imitation of an unpalatable and rejected species for protection—it is presupposed as a general postulate that the edible mimics are considerably in the minority, as Darwin showed; for if it were otherwise their enemies would soon discover that among the apparently unpalatable species there were some which were pleasant to taste. ”