by Grant Allen
Fruits rank second in beauty among vegetal organs. First in the list of creatures which feed upon fruits may be mentioned the whole tribe of parrots, macaws, and cockatoos, the brightest in hue of all birds, except the flower-feeders. Next we may place the toucans, with their gaudy beaks, and with them the hornbills. Then come the fruit-pigeons, whose gorgeous tints contrast strongly with those of their seed-eating congeners. After these succeeds a whole host of orioles, blue-birds, birds-of-paradise, plantain-eaters, and less conspicuous fruit-feeders, every one of whom has some beauty of colouring which recalls its habitual food. Again, the frugivorous bats, and the fruit-eating quadrumana, including the gorgeous mandrill, are the most highly-coloured of the Mammalia. Finally, the frugivorous lizards must not be forgotten among the list. Of these, the parrots, toucans, and fruit-pigeons have been specially modified to suit their peculiar food.
Third in point of colouring we may place the insects themselves, which have based their own beauty upon that of the flowers. The creatures which prey upon these may be divided into two classes, the partly frugivorous, and the wholly insectivorous. Among the former we may specially note as brilliantly-coloured the rollers, todies, motmots, many trogons, hoopoes, some birds-of-paradise, and jays. Among the latter we may note the dragon-flies and tiger-beetles, in the insect world itself; the jacamars, bee-eaters, fly-catchers, and many other bright small kinds of birds; and the Draco, with many less brilliant lizards. On the whole, these various animals are inferior in beauty of colour to the flower-feeders or fruit-eaters, but are still very bright in their hues. It should be further noted that most of them are closely allied with frugivorous or flower-haunting species, from which they may in some cases be descended, and that many live habitually in the midst of an environment distinguished for the general brilliancy of its colours.
Next, we may descend to these same creatures themselves, looked upon as tertiary causes of colouring in others. Among the bright objects which feed upon these birds or reptiles may be noticed many brilliant snakes and some lizard-eating birds. These, too, live amid an environment of considerable beauty.
Last on the list we may place the marine creatures, fishes or crustaceans, which pass their time among the gorgeous productions of tropical seas, and whose own colouring may possibly reflect that of their varied and exquisite surroundings.
Now let us look at the reverse picture of those classes which are specially deficient in pure and conspicuous colouring.
First in order of ugliness must be placed the carrion-feeders, who live upon decaying bodies or animal excrements. Among insects, we may notice the flies which swarm about carcasses or dung, several dingy beetles, and all the other ugly creatures which we always surprise in such situations. Among birds, the vultures, condors, turkey-buzzards, and other like obscenæ volucres, show correspondingly dull colours. Among mammals, the hyenas and jackals may fall nearly under the same category. It is worth notice that all these creatures have for naturally frugivorous man a certain weird and uncanny appearance, which seems not entirely dependent upon association with their hideous mode of life. It may also be observed that those races of mankind which have most fully adopted the habit of feeding upon carrion or filthy prey, such as worms, insects, &c., are often the blackest, most squalid, and least æsthetic of the whole human species.
Second in dinginess rank the nocturnal animals. Among insects, we have the moths, and many such tribes as earwigs and cockroaches. Among birds, we get the owls which exactly reproduce the moths in colour; besides the goat-suckers, the apteryx, and numerous other aberrant types. Among mammals, we have the mass of bats, and several quadrumanous animals. All these are remarkable for a certain general murkiness of hue, which cannot otherwise be described, but which can be felt as differing from the hideousness of the carrion-feeders on the one hand, and the cinereous tone of the carnivorous birds on the other. It should further be noted that the owls and bats have eyes specially modified for darkness, by the absence of the cones, which we have seen reason to conclude are the special organs of colour-perception; while I have already pointed out a corresponding structural peculiarity in the eyes of nocturnal insects. The subterranean mole may perhaps be grouped in the same class.
Third in this connection we may place the rapacious animals generally. Fishes supply us with the shark and pike. Reptiles include the crocodiles and many snakes. Birds yield instances in the Raptores as a whole, — eagles, hawks, falcons, — and in isolated cases such as the shrike. Mammals add the wolves, bears, and insectivores. The larger cats, however, together with the green snakes, must be specially excepted, their colouring, as we shall see hereafter, being protective in its arrangement. So, of course, must be the animals already enumerated among the brilliant class, which feed upon unusually bright-coloured prey.
Other cases must be roughly enumerated in a single paragraph. The larger marine creatures are usually dull: as witness whales, porpoises, walruses, seals, and turtles. Fresh-water animals are less bright than the smaller marine and terrestrial fauna: take for examples river-fish, fresh-water molluscs, water-beetles, otters, voles, coots, and most water-fowl. The mass of herbivores are quiet in colouring, though often pretty according to our developed Aryan taste. Omnivorous animals, like crows, pigs, and men, are not usually bright in their tints. Seed-eating birds have mostly grey or neutral plumage. Marine birds are, as a rule, whitish or grey. In short, the immense majority of animals which do not feed on bright-coloured food are of plain hues, in which black or white predominates, in certain muddy mixtures, with very little tinge of red, yellow, green, or blue, and with no spots, bands, or markings of pure analytic colours.
Lastly, intermediate between the two classes of brilliant and dull-coloured animals, we get what may be called the transitional stage. This stage shows a general tendency to pure colours, more or less subdued by plainer intermixtures; but it does not often exhibit perfectly unmixed shades of crimson or azure. It is represented in many insects, especially among the Lepidoptera and Coleoptera; in the remaining Insessores and gallinaceous birds; in squirrels, monkeys, and many frugivorous mammals; and in numbers of snakes, lizards, and amphibia. Most of these may be said to hover on the border between bright and dingy food-stuffs, varying from flies, grubs, slugs, brownish seeds, and small grey birds or mammals, to gay fruits, butterflies, birds’ eggs, banded snails, bright little reptiles, and birds of handsome plumage. As a whole, an approximate correspondence can be traced between the average brilliancy of their food and the average brilliancy of their own colouring.
If all these be mere coincidences, they seem to me without exception the most extraordinary coincidences ever observed in nature. But even a list such as this cannot at all adequately represent the real state of the case. I may therefore be pardoned if I mention that the generalisation here so insufficiently enforced has been thrust upon me by three separate sets of observations. First came my own constant observation, that within the sphere of my daily experience, in walks and excursions, in Europe, North America, and the West Indies, I found such a correspondence between bright food and bright colouring, or dull food and dull colouring, to obtain in a vast majority of cases. Secondly, visits paid for the purpose to the Zoological Gardens, the British and other Museums, and the various aquariums, in order to satisfy myself as to such correspondence, greatly increased my belief in its truth. After examining the several brilliant species, I made inquiry into trustworthy books as to the nature of their food, and I almost always found that the rough generalisation I had provisionally framed was thus greatly supported. I may add, too, that the mass of specimens, as seen in a garden or a cabinet, produces a far more vivid impression on the mind than is possible from the mere mention of isolated names. Thus a single instance, like that of the peacock or the flamingo, has great weight under ordinary circumstances, when thought of in isolation; but when one turns from a case full of the gallinaceous birds or the waders, to a case full of flower-haunting humming-birds or fruit-eating parrots, the difference
in the whole average of instances is seen to be simply infinite. Accordingly, I would strongly urge those who wish to judge of my theory for themselves, to make such careful comparisons in person, at some one of our great zoological collections. Thirdly and lastly, during the whole course of my reading in the works of traveller-naturalists, I have been invariably struck by the same connection of food and hue. Especially has this connection been thrust upon me once more by Mr. Wallace’s admirable work on “Tropical Nature,” which has appeared since the present volume was wholly planned, and in great part written. And since this theory is the part of my work to which I myself attach the greatest importance, and for which I expect the greatest amount of hostile criticism, I venture to add a few typical passages from my notes, gathered from those works which have so often stood us in good stead already, and jotted down in passing, while the theory was still vaguely evolving itself in my mind. They may help to show the reader the style of suggestion which comes upon one from every side with reference to this subject.
Of the fruit-pigeons, Dr. Jerdon says, “These pigeons are of very large size, with rich and metallic colours;” but of the ground pigeons and doves, which “feed chiefly on grains,” he observes, “they are of more dull and sombre colours.” Mr. Wallace speaks over and over again of similar species, such as the lovely little fruit-eating Ptilinopus pulchellus, which “is of a beautiful green colour above, with a forehead of the richest crimson, while beneath it is ashy white and rich yellow, banded with violet red.” Then we have the exquisite Nicobar pigeon, which eats “fallen fruits,” the “very handsome fruit-pigeon” (Carpophaga concinna), which lives on nutmegs, and the “pretty little flower-pecker” (Prionochilus aureolimbatus), whose name sufficiently declares its golden markings. Once more, Scissirostrum Pagei belongs to a family generally dull, but has yellow bill and feet, and a tail of “vivid crimson;” and on inquiry, we see that it feeds upon fruit. Soon after, we read concerning a flock of the “fine crimson lory (Eos rubra), a parroquet of a vivid crimson colour,” that “they settled down upon some flowering tree, on the nectar of which lories feed.” Then again we have the “large green barbets (Megalæma versicolor), something like small toucans, . . . whose head and neck are variegated with patches of the most vivid blue and crimson.” On another page we meet with a lovely small fruit-pigeon (Ptilinopus roseicollis), “whose entire head and neck are of an exquisite rosy pink colour, contrasting finely with its otherwise green plumage.” So, when we turn to Sir Emerson Tennent, we find the “very beautiful pigeon” Carpophaga Torringtoniæ; the exquisite flowers, haunted by lovely butterflies; and the magnificent bats and flying squirrels, which feed on fruits. Mr. Bates similarly tells us how along the Amazons the butterflies were found in great brilliancy on the flowery parts, while amongst them flitted “fiery red” dragon-flies; how “from the wild fruit-trees we often heard the shrill yelping of the toucans;” how the pretty cigana (Opisthocomus cristatus), a gallinaceous bird, eats various wild fruits, and how at one place on the river, where he “was surprised at the number and variety of brilliantly-coloured butterflies,” he also noticed the “glossy-green beak and rose-coloured breast” of a “beautiful bird” (Trogon melanurus), and the “golden-bronze and steel colours” of a jacamar (Galbula viridis), which fed on these very insects. On the other hand, he notes how, near Santarem, “the pastures are destitute of flowers, and also of animal life, with the exception of a few small plain-coloured birds.” I could multiply these instances by dozens, but I only select the first which I find on my notes, to show the sort of evidence which suggested and supported the theory, and by observing which it may be most easily confirmed. Indeed, whenever I find mention of any brilliant creature, be it Indian Goliath-beetle, South-American longicorn, scarlet-faced monkey, gay-coloured squirrel, handsome bats, or fairy blue-birds, I almost always notice, either coupled with the fact, or on further search, that the animal in question feeds upon bright-coloured food.
It will perhaps seem like pushing the conclusion beyond reasonable limits if I go on to say, that in some cases one may even possibly detect a correspondence in actual tint between the animal and its food. Yet even this appears not wholly impossible. Of course no stress can be laid on some two dozen or so of such instances, some of which may be really protective; but the hint is worth throwing out, for future verification or disproof, as the case may be.
And now that we have completed this part of our inquiry, let us once more return to Mr. Wallace’s objection against sexual selection, from the root upward. When we were considering its applicability to insects, I pointed out that the “theory of typical colours” really suffices to cover the whole difficulty; and the same argument will apply to vertebrates; for if recognisability is a requisite of the typical colouring, it may well happen that those species which feed on brilliant objects, being always on the look-out for patches of colour, will be mutually attracted to one another; and the taste thus set up and strengthened from generation to generation may become an additional cause for differentiating the nascent species from others of different habits. As the taste for brilliancy and the frugivorous mode of life will go hand in hand with one another, it will naturally happen that some variety of colour will become the recognised differentia of the particular species, whereby its members mutually know their own fellows from all other kinds. And at the same time, inasmuch as all species of flower-feeders and fruit-eaters are not coloured alike, and have not the same ornamental adjuncts, I fail to see the force of Mr. Wallace’s argument that all individuals seem to pair off in the long run; for the æsthetically-endowed individuals would pair off with one another, while the æsthetically-deficient would be left for their likes; and the difference thus initiated, correlated as it must necessarily be with other peculiarities of taste and habit, would become in turn the starting-point for a fresh differentiation. Indeed, if I may say so without presumption concerning so great a naturalist, Mr. Wallace seems to me here to have fixed his eyes rather upon the product, the made species, than upon the process, the species-making.
Moreover, it is noteworthy that among these same brilliant creatures, which owe their colours ultimately to their bright-hued food, we find the greatest profusion of other apparently æsthetic and sexual ornaments. The butterflies, besides their colours, are remarkable for their queer tails and other appendages, as well as for those allurements of scent which F. Müller has pointed out. The beautiful fishes are likewise the species in which strange excrescences occur. The lizards have an immense number of ornamental devices, like pouches, knobs, and horns. The humming-birds and sun-birds are distinguished by their ruffs, crests, lappets, and tail-feathers. The parrots and birds-of-paradise affect similar tricks of plumage; which are also found in the hoopoes and many of the semi-brilliant class. The handsome gallinaceous birds have combs and wattles. And while we find few such ornamental modifications among the lower Mammalia, it is a fact pregnant with import that the frugivorous and arboreal rodents or quadrumana repeat the very same peculiarities of crests, tufts, and beards which are so common amongst the similarly-environed forest birds. Any one who will take the trouble to look through the immense collection of instances in Mr. Darwin’s “Descent of Man,” will see at a glance that the most brilliant tribes are also, on the whole, the most ornamented.
On the other hand, one may hazard the rough generalisation, that the animals which appeal to their mates by the sense of hearing are not those which appeal by the sense of colour. The stridulating insects and the singing birds are usually plain in their external appearance. It might seem as though the habits of some races had led them to attach more importance to sounds, while the habits of others led them to attach more to colour. In any case, we may be quite certain that no such taste is fortuitous and isolated. It must bear some definite relation to the general mode of life throughout the race.
One more question remains. Mr. Wallace observes with great truth that colour may be regarded as a normal product of organisation, whose presence in animals doe
s not need to be explained so much as its absence. But the difficulty at once crops up — what colour? I have not space fully to follow up this ultimate problem; but we may find room for a few brief suggestions.
Almost all the ornamental appendages of animals are modifications of the skin or its equivalent. They are found most frequently and strikingly in the male sex: and they are most conspicuous during the breeding season. Whatever we may think of their functions, we must agree that they are, on the whole, products of high vitality. They represent part of the excess of nutriment over expenditure.
But these dermal adjuncts do not probably take away anything from the effective energies of the organism. As Mr. Lowne well puts it, in his able and suggestive work on “The Philosophy of Evolution,” the formation of pigments and like matters is apparently due to the waste-products of the other organs. “The dermal appendages of reptiles and the feathers of birds, rich in pigment and nitrogen, are probably entirely excrementitious to the other tissues, and, without doubt, depend in great part for their origin on the solid nature of the excretion of the kidneys. Birds especially, leading a very active life, excrete material rich in nitrogen; and the feathers, which are shed periodically, enable them to throw off that element without overtaxing their renal organs.” And again, “A given pabulum being supplied, certain essential structures are nourished, and the residue is economised in the production or modification of other parts, often giving rise to ornamental appendages or bright colours; whilst the action of the same principle correlates the modifications of different organs or parts with each other.”
Hence we can understand why the more active and energetic sex should possess a greater number of highly developed dermal adjuncts, and should often display much brighter colours than the females. We can also see why these integumentary modifications should be largest and most expanded in the most active races, such as butterflies, birds, flying-lizards, and arboreal mammals; while conversely, the possession of these very organs, in the case of flying animals at least, is itself a cause of their increased locomotive power. Here we notice a remarkable instance of that close interaction between structure and function which has been pointed out by Mr. Herbert Spencer, — the function first developing the structure, and each increment of structure permitting increased function, which once more becomes in turn the parent of further structural modifications.
