The Zoologist/4th series, vol 2 (1898)/Issue 689/Biological Suggestions. Assimilative Colouration

by William Lucas Distant

 

THE ZOOLOGIST

 

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No. 689.—November, 1898.

 

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BIOLOGICAL SUGGESTIONS.
ASSIMILATIVE COLOURATION.

By W.L. Distant.

(Continued from p. 409.)

Part II.

 

Fish appear to vary in colour and in an assimilative manner to the hue of the water in which they are confined.^[1] According to Frank Buckland, "this is the case particularly with Minnows, Sticklebats, and Trout. Mr. Grove, the fishmonger at Charing Cross, will tell you where a Trout comes from by its colour. The Trout which live in peat-coloured water are sometimes nearly black; those from fine running streams, such as the clear chalk streams about Winchester, are of a beautiful silvery colour. Gudgeons placed in a glass bowl will become very white, and lose the beautiful brown colour on their backs." "A fishmonger at Billingsgate Market told me he generally knew from what part of the coast fish came by the colour of them. This observation was à propos to a quantity of Dutch Jack that were displayed on his slab; and which looked very dingy and dark-coloured, as though they had lived in stagnant and dirty water; very different from a clean and bright-coloured Thames Jack." "Sticklebacks are wonderful fish to change their colour. I have seen Sticklebacks at the tail of a mill pond at I slip of the most beautiful iridescent colour; the bottom was composed of clean white gravel stones. Again, there is a ditch running round Christchurch meadow at Oxford; here the water is black and dirty, and the Sticklebacks are of a brown and almost black colour."^[2] The same author considers that "the Black-backed Salmon" of the Galway river "are fish which have spent most of their lives in dark bog-coloured water, and hence they have assumed the peculiar dark appearance they present, for, as we all know, the colour of the fish is wonderfully influenced by the colour of the water in which it lives."^[3] There is a well-known rock on the coast of Cornwall, about five leagues from the land, and standing up from the plain ground which spreads to a large distance round it. The top of the rock is full of gullies shaded with weeds, and Congers which are caught on it are always black, while close to its base these fish are always white.^[4] From Great Yarmouth it is reported that Flounders (Pleuronectes flesus) when sea-caught are lighter hued than those taken on a muddy bottom.^[5] "The Sunfish (Labrus auritus, Linn.) caught in the deep waters of Green River in Kentucky exhibit a depth of olive brown quite different from the general tint of those caught in the colourless waters of the Ohio or Schuylkill; those of the reddish-coloured waters of the bayous of the Louisiana swamps look as if covered with a coppery tarnish; and, lastly, those met with in streams that glide beneath cedars or other firs have a pale and sallow complexion."^[6] A no less authority than Dr. Günther states: "Trout with intense ocellated spots are generally found in clear rapid rivers, and in small open alpine pools; in the large lakes with pebbly bottom the fish are bright silvery, and the ocellated spots are mixed with or replaced by X-shaped black spots; in pools or parts of lakes with muddy or peaty bottom the Trout are of a darker colour generally, and when enclosed in caves or holes they may assume an almost uniform blackish colouration."^[7] "Minnows have the power common to most fishes of rapidly assimilating to the varying colour of the stream. They change from brown to gold, from gold to brown."^[8] The Paradise-fish (Polyacanthus sp.), a pet kept in confinement throughout China, has a colour in dark or muddy waters of a "dull uniform brown; and it is only when living in clear water, exposed to the sunlight, that the golden hue and red transverse bands make their appearance." "Cod from the British seas and German Ocean are usually greenish or brownish olive in colour, with a number of yellowish or brown spots; but more to the north darker, and often uniformly coloured specimens are more common; while in the race from Greenland, Scandinavia, and northern Norway, there is frequently a large irregular black patch on each side of the body."^[9] In the South Atlantic Mr. Cunningham secured by the aid of the towing-net a bright blue Isopodous crustacean (Idotea annulata), and states that, according to Spence Bate, "the blue colour appears to be a peculiarity of pelagic species."^[10]

Entomologists have long noticed the effects of assimilative colouration, even in our own country. Mr. Dale, of Glanvilles Wootton, has truly remarked: "Where do we find whitish or brilliant-coloured species of Lepidoptera, such as Melanargia galatea, Lyccena corydon, L. adonis, Eubolia bipunctaria, Melanippe procellata, and the light variety of Gnophos obscuraria, &c.? Why, on the white and light-coloured soils of the south of England, i.e. chalk and limestone. On the other hand, we find the dark variety of G. obscuraria, and various dark-coloured species, on black peaty soils."^[11] A noctuid moth, Agrotis lucernea, not uncommon in Britain, when found on the chalk downs in the Isle of Wight has been thus described: " It rests in chinks on the ground, and is of a soft silky grey colour, and covered with such thick and long scales as to give it a furry appearance. Although abundant enough by night, it requires a long search to find a single specimen by day, so difficult is it to distinguish in its native haunts, the long pale silky hairs resembling exactly the rough surface of the chalk dusted with the darker atoms of the soil above." This moth has also been caught by the same entomologist on the east coast of Scotland, and then thus differently described: "On black rocks, sometimes reeking with moisture, and which were as black as the rocks on which they rested." Mr. Tutt, to whom we are indebted for these notes and observations, ascribes the colouration in each case as due to the action of natural selection. We may at least say in respect to other instances he has adduced that this explanation is not so apparent. Noctua glareosa "is of a pale dove-coloured grey, sometimes tinged with rosy," and with three dark spots. "The Sligo specimens are very white,—Scotch specimens more slaty; the Shetland specimens are of a rich blackish brown colour."

Epunda lichenea "is a mottled greenish grey or greenish ochreous species, which is confined to a few coast districts. The Portland specimens are greenish white; the Teignmouth specimens dark greenish ochreous, mottled with red. The moths from these two localities have quite a different appearance, owing to the different kind of rocks on which they rest at these places." Amphidasys betularia, a Geometrid moth, "as it rests on a trunk in our southern woods, is not at all conspicuous, and looks like a natural splash or scar, or a piece of lichen "; but near our large towns, where there are factories, and where vast quantities of soot are day by day poured out from countless chimneys, this moth "has during the last fifty years undergone a remarkable change. The white has entirely disappeared, and the wings have become totally black, so black that it has obtained the cognomen 'negro' from naturalists."^[12] The dipterous insect Cœlopa frigida undergoes its transformations in the black sea-weed cast up by the spring tides. The flies and also the pupæ are black.^[13] In a revision of the American orthopterous genus Spharageomon, Mr. Morse states: "Variation in colour in this genus, in common with other Œdipodinæ, counts for very little; the same species or race may be of all shades from a general dark fuscous to a pale buff or even a bright reddish brown, even in specimens from the same spot, yet it is probable that the general tint of a large series will be found to agree with the colour of the soil of the locality, or other peculiarity of environment. Specimens of different species from different localities in Colorado show a striking reddish almost rosaceous colouration due to some such cause."^[14] Of course this can only apply to the insects when at rest, otherwise their more gaily-coloured under wings would contradict the view advocated. A. previous American writer, Mr. Brunner, had proposed that climatic differences had accounted for the varied colouration of the wings of some North American Locusts.^[15] Eimer has some excellent observations on this point, and with these insects:—"The Grasshopper with red hinder wings banded with black, which is so common with us (in Germany) in summer, Acridium germanicum (Œdipodea germanica), when it occurs on the reddish brown Triassic clay of Tubingen, resembles this ground so closely with its wings folded that it cannot be distinguished from it. A little above the clay on the hills of this neighbourhood there occurs a whitish sandstone, sometimes only for the breadth of a path or in somewhat larger surfaces, frequently surrounded by the former. On these small patches of lighter ground I find regularly only Grasshoppers with quite light upper wings, so that they can scarcely be distinguished from the soil. And I have elsewhere observed the same remarkable adaptation. One of my friends who is not usually accustomed to pay special attention to such animals, told me that he had been much surprised to notice that on the two banks of a brook on which the soil was of different colours, the Grasshoppers were in each case exceedingly like the ground in colour. Without doubt these were Acridium germanicum or A. cærulescens,—the latter species appears to show the same adaptation."^[16] Canon Tristram in his North African travels met with an area of the limestone conglomerate with earlier pebbles, in which a fine white flint, not previously observed, predominated. Here, to use his own words, "we found only two living things through the whole day—a curious white Scorpion, and a Desert Lark (Annomanes regulus, Bp.)."^[17] In Kamschatka, where the ground is so long covered with snow, Mr. Guillemard, in comparing the Great and Lesser Spotted Woodpeckers, the Capercailzie, and the Marsh Tit, with the forms found in Europe, remarks: "In all these the differences consist for the most part in the greater predominance of white in the plumage, and this tendency to albidism is noticeable, as I have already mentioned, in other animals besides the birds; the Dogs and Horses likewise showing it in a marked degree."^[18] Sometimes the effect may be very sudden and of an artificial character. It is difficult to explain the process as described by C.J. Andersson in South Africa:—"In the course of the first day's journey, we traversed an immense hollow, called Etosha, covered with saline incrustations, and having wooded and well-defined borders. Such places are in Africa designated 'salt-pans.' The surface consisted of a soft greenish yellow clay soil, strewed with fragments of small sandstone, of a purple tint. Strange to relate, we had scarcely been ten minutes on this ground when the lower extremities of ourselves and cattle became of the same purple colour."^[19]

One of the most explicit observations bearing on this phase of animal colouration has been contributed by the late Mr. J.J. Monteiro. In Angola he found that in the districts where indications of copper were found, "the 'Plantain-eaters' are also most abundant, more so than in any other part of Angola I have been in";... "the most singular circumstance connected with this bird is the fact that the gorgeous blood-red colour of its wing feathers is soluble, especially in weak solution of ammonia, and that this soluble colouring matter contains a considerable quantity of copper, to which its colour may very probably be due. My attention was first called to this extremely curious and unexpected fact by Prof. Church's paper in the 'Phil. Trans.' for 1869; and on my last voyage home from the coast, I purchased a large bunch of the red wing feathers in the market at Sierra Leone, with which my brother-in-law, Mr. Hy. Bassett, F.C.S., has verified Prof. Church's results conclusively, and has found even a larger proportion of copper in the colouring matter extracted from these feathers."^[20] This colour, however, as we might surmise, was sufficiently independent of the copper to have become constant, for Mr. Monteiro kept two birds in confinement in England, during which time they moulted regularly every year, "and reproduced the splendidly coloured feathers, of the same brightness, without the possibility of getting any copper, except what might have entered into the composition of their food, which was most varied, consisting of every ripe fruit in season, cooked vegetables and roots, rice, bread, biscuits, dried fruit, &c." On the other hand, Dr. Bowdler Sharpe was informed by the late African traveller, Jules Verreaux, "that the bird often gets caught in violent showers during the rainy season, when the whole of this brilliant red colour in the wing feathers gets washed out, and the quills become pinky white, and after two or three days the colour is renewed, and the wing resumes its former beauty."^[21] This cannot be taken as an instance of pure but only partial assimilative colouration, but is sufficient to prove that colour may be largely derived from the mineral constituents of the earth's surface, and in this way can scarcely be altogether ascribed to the action of "natural selection." These bright wing feathers may have subsequently served the purpose of "recognition markings"?, but seem certainly not derived directly for that purpose.

A better example may be found in the Red Hartebeest (Alcelaphus cokei). Sir H.H. Johnston narrates of this species: "Being a deep red-brown in colour, and standing one by one stock-still at the approach of the caravan, it was really most difficult and puzzling sometimes to know which was Hartebeest and which was ant-hill; for the long grass hiding the Antelope's legs left merely a red-humped mass, which, until it moved, might well be the mound of red earth constructed by the white termites. The unconscious mimicry was rendered the more ludicrously exact sometimes by the sharply-pointed flag-like leaves of a kind of squill—a liliaceous plant—which frequently crowned the summit of the ant-hill or grew at its base, thus suggesting the horns of an Antelope, rather with the head erect, or browsing low down. The assimilation cannot have been fancied on my part, for it deceived even the sharp eyes of my men; and again and again a Hartebeest would start into motion at twenty yards distance, and gallop off, while I was patiently stalking an ant-hill, and crawling on my stomach through thorns and aloes, only to find the supposed Antelope an irregular mass of red clay."^[22] This would seem to be almost an instance of acquired or active mimicry on the part of this animal. Here the whole question to be considered is what was the original home of this Red Hartebeest? Is it a creature of these red-earthed plains, the character of which is so prominently shown in these gigantic ant-hills? Dr. Hans Meyer remarks that "every observer must be struck with the general similarity in colour and partly also in form of the larger African mammals to the prevailing colours and features of the regions they frequent. At a distance it is scarcely possible to tell a Hartebeest at rest from one of the reddish ant-heaps which everywhere abound; the long-legged, long-necked Giraffe might easily pass for a dead mimosa, the Khinoceros for a fallen trunk, the grey-brown Zebra for a clump of grass or thorn scrub. It is only their movements that betray their real character."^[23] The Lichtenstein Hartebeest (Bubalis lichtensteini) is also of a more or less uniform colour, "saffron, with a golden tinge throughout"; while the more common Hartebeest (Bubalis caama), which has a wider distribution, is also in general colour of a "reddish brown, with violet tinge throughout"; and Messrs. Nicolls and Eglington, who have been quoted as to the colour of both these animals, describing the habits of the last, write:—"The Hartebeest is never met with in very thick bush, or hilly country, but frequents either the bare open flats or plains sparsely covered with camel-thorn trees (Acacia giraffæ), and where there are treeless glades to be met with."^[24]

It may have possibly struck the reader by this time that the surmise of the writer is that, in the first instance, and in the long past, animals were uniformly and assimilatively coloured in connection with their principal surroundings, and that as they migrated through scarcity of food owing to excessive multiplication or other causes, or through the alteration of climatic condition, their changed environment placed them under altogether different conditions, and the modifying influence of natural selection then became a magician's wand in the evolution of diverse colours and markings, but it was not the sole agency. The tendency to explain all problems by the theory of natural selection is to-day greatly retarding the study of bionomics. It is not one whit removed from the proferred explanation of the old teleologists, and represents as little thinking. This has naturally not escaped the thoughtful consideration of Mr. Wallace, though he seems inclined to ascribe the early uniform colouration to a protective origin,^[25] whereas it is difficult to see that the same hue was equally protective to friend and foe, to the devourer and devoured.

A fact, however, which very strongly stands against the view of original assimilative colouration here assumed is found in the markings of the young of all the unicolorous cats,—Lion, Puma, &c,—which are more or less indistinctly spotted or striped, and as many allied species, both young and old, are similarly marked, Darwin has observed that " no believer in evolution will doubt that the progenitor of the Lion and Puma was a striped animal, and that the young have retained vestiges of the stripes, like the kittens of black Cats, which are not in the least striped when grown up. Many species of Deer, which when mature are not spotted, are whilst young covered with white spots, as are likewise some few species in the adult state."^[26] If this was a concrete fact, it would be fatal to the suggestion here made, but the evidence is not all one way, for, according to the late Prof. Kitchen Parker, in the Hunting Leopard (Cynœlurus jubatus) the young "are covered with soft brown hair, without spots, quite reversing the usual order of things"^[27]; and Col. Pollok states the same thing.^[28] However, per contra, Mr. Lydekker observes:

"It is stated that if a cub in this state be clipped, the under fur will exhibit distinct spotting."^[29] In the Lion the markings are also fœtal, for Steedman, quoting the particulars of a Lion hunt from the pages of the 'United Service Journal' (August, 1834), relates of a Lioness that was killed, "she had four unborn whelps, with downy skins, striped like the Tiger."^[30] It still appears that the young of many unicolorous animals are spotted. "Pigs and Tapirs are banded and spotted when young; an imported young specimen of Tapirus bairdi was covered with white spots in longitudinal rows, here and there forming short stripes. Even the Horse, which Darwin supposes to be descended from a striped animal, is often spotted, as in dappled Horses; and great numbers show a tendency to spottiness, especially on the haunches."^[31]

Similar markings are to be found in the young of many fishes. Larval Cod have black transverse bars, "the stellate black chromatophores arranged in bands are clearly indicated."^[32] Young Ling (Molua molva), when grown to a length of seven inches, pass through a very distinct barred stage.^[33] The young of all the Salmonidse are barred; "and this is so constantly the case that it may be used as a generic, or even as a family character, not being peculiar to Salmo alone, but also common to Thymallus, and probably to Coregonus."^[34] When the fry have attained a length of some four inches, they are known by the name of " parr," and "bear conspicuously on their bodies transverse marks or bars, which are common to the young of every member of the Salmon family."^[35] Even as regards the colouring of British land and freshwater Mollusca, the view has been held that Helix cantiana, H. cartusiana, &c, were once banded species.^[36]

Taking the cases of the Lion, Puma, and Cheetah, we see that the two first, unicolorous in their adult stage, apparently show by their spotted young a derivation from a similarly coloured ancestor, whilst the spotted Cheetah, from the apparent evidence of its unicolorous young, would point to a totally different conclusion. But the cumulative opinion of evolutionists is that all spots, stripes, and other prominent markings, have been intensified, preserved, or made permanent by a selective process, and have become, and are, of the greatest utility to the animals which possess them. Eimer, on the contrary, from the evidence of the markings on Cats and Dogs, is inclined to ascribe such markings as "due to external conditions and an internal direction of evolution, and can be acquired and inherited in spite of all pammixes"^[37]—cessation of selection, or the present non-importance of such characters in the struggle for existence. Mr. A. Tylor's views ('Colouration of Animals and Plants'), as summarized by Mr. Wallace, were that the primitive form of ornamentation consisted of spots, the confluence of these in certain directions forming lines or bands; and these again sometimes coalescing into blotches, or into more or less uniform tints covering a large portion of the surface of the body.^[38] It seems, however, more in consonance with present knowledge and opinion to consider that spots, though primitive, were not original, and succeeded, not preceded, unicolorous ornamentation, which has survived only where it has been more or less in unison with the creature's environment, and so afforded "aggressive protection," as in the case of the Lion. Some of the best observations on this point are often made by travellers who know little of the subject, are not zoologists, have no preconceived ideas, but possess a clear mind with which to observe common facts. Such an observation on the colour of the Lion is to be found in a recent book written by two ladies recounting their experiences in Mashonaland:—"His coat was soft and bright, and of a tawny colour—not unlike that of a mastiff—with black points. This colour is so like that of the sun-dried grass, that it can with difficulty be distinguished from it."^[39] If, however, it may be considered as rash to speculate on an original unicolorous or assimilative colouration, it seems even more opposed to evolu- tionary ideas to predicate that because a mammal, as we know it at the present time, has a striped coat, it had also the same appearance in past geological epochs. Yet this seems to have been the method of Prof. Heilprin, who has written so excellently on the distribution of animals, considered geologically as well as geographically. Thus we read:—"The striped Hyena may be traced back to the older (Pliocene) H. arvennensis of Central France, and the brown form not improbably to the Miocene (or Pliocene) H. exima of Pikermi, Greece."^[40] At the present day we have brown, spotted, and striped Hyenas (H. brunnea, H. crocuta, and H. striata) all found in, though not confined to, the continent of Africa, and however they may differ osteologically, and however distinctly these differences may be detected in fossil forms, yet surely we are not warranted in concluding that identity of colouration has survived from the geological past. But speculating on the generally accepted conclusion that spots and stripes succeeded a uniform or concolorous decoration, and re- membering that the three forms of markings referred to can almost be found at the present time, it seems we ought to be very cautious, as evolutionists, in concluding that the Hyena had developed either spots, or stripes, in Miocene or Pliocene times. Remembering the numerous remains of the genus found in the Pleistocene deposits of Europe, and that, as Prof. Heilprin remarks, it was from these north temperate regions "the Ethio- pian realm has drawn much of its existing distinctive fauna," and that the widely distributed Cave Hyena (H. spelæa), if not identical with the present spotted form (H. crocuta), was "without doubt its direct ancestor," it remains a suggestion as to what the original colouration was, altogether apart from structural specific distinction. Among the fossils of Pikermi, Gaudry found the successive stages by which the ancient Civets passed into the more modern Hyenas.^[41]

If the view of original assimilative colouration is reasonable and probable, then it should receive support from the generally understood derivation of spots and stripes by a process of "natural selection," though, as we suggest, and as will be explained later on, natural selection must be regarded as a permitting and perpetuating force, rather than as a creative agency.^[42] Two instances will here suffice for a consideration of this point in colouration, and are both based on the observations of two competent and excellent observers. The first relates to that prominently striped animal the Zebra, and was made by Mr. F. Galton:—"No more conspicuous animal can well be conceived, according to common idea, than a Zebra; but on a bright starlight night the breathing of one may be heard close by you, and yet you will be positively unable to see the animal. If the black stripes were more numerous he would be seen as a black mass; if the white, as a white one; but their proportion is such as exactly to match the pale tint which arid ground possesses when seen by moon-light."^[43] The second observation was made by that renowned sportsman, General Douglas Hamilton, and relates to the Spotted Deer and Tiger in India:—"For example, the Axis, or Spotted Deer as it is generally called, is something like the Fallow Deer in colour, only the white spots and markings are more distinct, and the body is a brighter red; one would imagine such a conspicuous animal could be easily distinguished in the forest, but the spots and colour so amalgamate with the broken lights and shades that I have often taken a shot at which I thought was a solitary Spotted Deer, and have been astonished to see ten or twelve dash away. The Tiger, again, with his bright body, black stripes, and white markings, is most difficult to see in the forest, arid even on the open hill side; at three hundred or four hundred yards distant not a stripe is distinguishable. More than once I have mistaken a Tiger for a light-coloured hind Sambur, until I have brought the telescope to bear and seen my mistake."^[44] General Kinloch, as quoted by Lydekker, referring to the Spotted Deer, says, "unless it moves, few beasts are more difficult to see; the colour of the skin harmonizes with the dead leaves and grass, while the white spots are indistinguishable from the little flecks of light caused by the sunshine passing through the leafy branches."^[45] These observations have the great merit of being neither the result of preconceived opinion, nor the effort to support a theory. Mr. Galton's journey was made during the years 1850–2, before the advent of that epoch-making work the 'Origin of Species,' which at once rivetted attention on all these phenomena. General Douglas Hamilton simply recorded the impressions of a sportsman with thirty-five years' experience in India. Such testimony cannot be gainsaid, and though numerous other illustrations could readily be compiled, and from the pens of capable observers, those here given will suffice as regards the standard of competence and accuracy. On the other hand, I was surprised, in reading the 'Travels and Adventures in South East Africa' of that celebrated and experienced hunter, Mr. P.C. Selous, that he seemed to have no similar observations to record.

In reference to the above instances of spots and stripes affording concealment, the explanation of "active mimicry," as I hope to advocate subsequently, might be applied; but then it must be remembered that the same phenomenon is found in other animals who live under very different conditions. Thus the Zebra Shark (Stegostoma tigrinum) is marked with black or brown transverse bars or round spots. Again, in Australia, according to Prof. Strong, the Rabbit is not only often parti-coloured, but numerous instances occur not only of white and black Rabbits, but of Rabbits "with beautifully striped skins."^[46]

The origin of spots and stripes is shrouded in obscurity. In domesticated animals, such as Dogs, Cats, cattle, and Horses, unsymmetrical markings constantly occur. According to Mr. Wallace, "Such markings never occur in wild races, or if they occur in individual cases they never increase; and I have given reasons for thinking that symmetrical colour and marking is kept up in nature for facility of recognition, a factor essential to preservation and to the formation of new species."^[47] Mr. Bateson combats the view that variability of domestic animals is markedly in excess of that seen in wild forms. He adduces the great variability of the teeth of the large Anthropoids compared with the rarity of variations in the teeth of other Old World Monkeys, and the comparative rarity of great variations even in man:—"If the Seals or Anthropoids had been domesticated animals, it is possible that some persons would have seen in their variability a consequence of domestication."^[48] As regards colour, the same author is more emphatic. To use his own example:—"I go into the fields of the north of Kent in early August, and sweep the Ladybirds off the thistles and nettles of waste places. Hundreds, sometimes thousands, may be taken in a few hours. They are mostly of two species, the small Coccinella decempunctata or variabilis and the larger C. septempunctata. Both are exceedingly common, feeding on Aphides on the same plants in the same places at the same time. The former—C. decempunctata—shows an excessive variation both in colours and in pattern of colours, red-brown, yellow-brown, orange, red, yellowish white, and black in countless shades, mottled or dotted upon each other in various ways. The colours of Pigeons or of cattle are scarcely more variable. Yet the colour of the larger C. septempunctata is almost absolutely constant, having the same black spots on the same red ground. The slightest difference in the size of the black spots is all the variation to be seen. (It has not even that dark form in which the black spreads over the elytra until only two red spots remain, which is to be seen in C. bipunctata.) To be asked to believe that the colour of C. septempunctata is constant because it matters to the species, and that the colour of C. decempunctata is variable because it does not matter, is to be asked to abrogate reason."^[49]

If we consult Mr. Gladstone's 'Impregnable Rock of Holy Scripture,' we shall be induced to believe that such markings may have arisen by a partial or further process of assimilative colouration. According to the Biblical narrative, the astute Jacob in his negotiations with Laban increased the number of "ringstraked, speckled, and spotted" cattle by the following ingenious method. He "took him rods of green poplar, and of the hazel and chestnut tree; and pitted white strakes in them, and made the white appear which was in the rods. And he set the rods which he had pitted before the flocks in the gutters in the watering troughs when the flocks came to drink, that they should conceive when they came to drink. And the flocks conceived before the rods, and brought forth cattle ringstraked, speckled, and spotted."^[50] This narrative might be used as a theological argument for the theory that wild animals may have acquired their spots and stripes in a similar manner, as the Tiger in his bamboo jungle, &c, and it seems strange in these plentiful days of theory that no clerical evolutionist has advanced such a view. Canon Tristram, however, by his observations in the Sahara, does not advocate this suggestion, for in these desert plains he described sheep in which "Jacob's ringstraked and speckled, dappled with white, and especially light brown predominated."^[51]

Another suggestion, to which allusion has already been made, is that of the late Alfred Tylor, who starts with the premiss that it "seems most probable that the fundamental or primitive colouration is arranged in spots,"^[52] and that these are capable of being coalesced into bands, stripes, and blotches, and are structural in affinity. "If we take highly decorated species, that is, animals marked by alternate light and dark bands, or spots, such as the Zebra, some Deer, or the carnivora, we find first that the region of the spinal column is marked by a dark stripe; secondly, that the regions of the appendages, or limbs, are differently marked; thirdly, that the flanks are striped or spotted along or between the regions of the lines of the ribs; fourthly, that the shoulder and hip regions are marked by curved lines; fifthly, that the pattern changes, and the direction of the lines, or spots, at the head, neck, and every joint of the limbs; and lastly, that the tips of the ears, nose, tail, and feet, and the eye are emphasized in colour. In spotted animals the greatest length of the spot is generally in the direction of the largest development of the skeleton."^[53] Mr. Tylor had assuredly not read an African observation made by the late Dr. Livingstone, or he would have as certainly incorporated it in his essay as evidence for his theory, and which it may be almost said to have partly anticipated. Dr. Livingstone writes:—"The Poodle Dog Chitane is rapidly changing the colour of its hair. All the parts corresponding to the ribs and neck are rapidly becoming red; the majority of country Dogs are of this colour."^[54] Emin Pasha does not corroborate this statement of Livingstone respecting the markings of Central African Dogs. He describes them as "usually of a buff colour."^[55] As regards the reddish colour of the Central African Dogs as described by Livingstone, it must be remembered that many domesticated Dogs are considered to have been the result of taming different wild species of Canidae, and that the Black- backed Jackal (Canis mesomelas), which is found from Nubia to the Cape, has a light red skin with a black dorsal stripe. According to Lydekker, in the Prairie Wolf of North America (Canis latrans), "the colour varies considerably at different seasons of the year, being of a bright fulvous-brown in summer, and grey or greyish in winter; this ground colour at both seasons being overlaid with a shading of black, which tends to form stripes along the back and across the shoulders and loins."^[56] Another peculiarity in African Dogs has been recorded by Blumenbach:—"The Guinea Dog (which Linnæus calls C. ægyptius—I do not know why) is, like the men of that climate, distinguished for the velvety softness of his smooth skin, and the great and nearly specific cutaneous perspiration."^[57] Darwin, discussing the animals under consideration, is inclined to ascribe spots and stripes as due to his theory of "sexual selection," the ornamentation having firstly been acquired by the males, and then transmitted equally, or almost equally, to both sexes. He adds: "After having studied to the best of my ability the sexual differences of animals belonging to all classes, I cannot avoid the conclusion that the curiously-arranged colours of many Antelopes, though common to both sexes, are the result of sexual selection primarily applied to the male."^[58] And he subsequently remarks: "Nevertheless, he who attributes the white and dark vertical stripes on the flanks of various Antelopes to this process will probably extend the same view to the royal Tiger and beautiful Zebra."^[59] Mr. Wallace estimates the derivative process of spots and stripes as a purely protective one:—"In mammalia we notice the frequency of rounded spots on forest or tree-haunting animals of large size, as the forest Deer and the forest Cats; while those that frequent reedy or grassy places are striped vertically, as the Marsh Antelopes and the Tiger." And again: "It is the black shadows of the vegetation that assimilate with the black stripes of the Tiger; and in like manner, the spotted shadows of leaves in the forest so harmonize with the spots of Ocelots, Jaguars, Tiger-cats, and Spotted Deer, as to afford them a very perfect concealment."^[60] This last view seems borne out by all the facts at our disposal, and as adaptation implies a previous state of variation, which again predicates a more or less stable condition from which variation arose, we come to the conclusion that the pre-variable condition was a unicolorous one, and from the data—scanty indeed—at our disposal, are inclined to suggest that the unicolorous hue was originally due to assimilative colouration. The wild Horse of Asia is said to be of a dun colour, while those of South America are described as commonly chestnut or bay coloured.^[61] Why is this?—the question bristles with present difficulties. In the writings of pre- and anti-Darwinian naturalists are often found remarks and statements unconsciously supportive of the future theory. Thus Charles Waterton, in describing the faunistic features of the Demerara forest, writes: "The naturalist may exclaim that nature has not known where to stop in forming new species, and painting her requisite shades"^[62]; while Frank Buckland from a teleological point of view had pointed out that the striped coat of the Tiger was "most suited" to his environment, and "when skulking through the dark shade, either of corinda or jungle, it would be almost impossible to make out his huge cat-like carcass creeping along like a silent shadow."^[63] Eimer also observes:—"I have permitted myself to express the supposition (Varüren, &c.) that the fact of the original prevalence of longitudinal striping might be connected with the original predominance of the monocotyledonous plants whose linear organs and linear shadows would have corresponded with the linear stripes of the animals; and further, that the conversion of the striping into a spot-marking might be connected with the development of a vegetation which cast spotted shadows. It is a fact that several indications exist that in earlier periods the animal kingdom contained many more striped forms than is the case to-day."^[64] To even fancy the appearance of animal and plant life in past geologic epochs, apart from structure as revealed by palaeontology, is left to sober scientific imagination. We know there was a flowerless age, but even then animal life existed. Is it to be argued that such animal life had reached its development in colouration? Can we not more easily imagine that animals assimilated in colour with the monotonous and semi-sombre hues of their then environment; but as they multiplied and the struggle for existence caused migration, the same inherent tendency to assimilative colouration prompted assimilative variation in response to the difference in surrounding conditions, and when this variation became adaptive and protective, the process of natural selection accentuated and perpetuated whatever was advantageous to the creature's existence.

The late Andrew Murray, in a paper read before the British Association in 1859, and just before or coincident with the appearance of Darwin's 'Origin of Species,' appears to have held a similar impression, though not reaching the explanation of "natural selection." His words well serve to conclude this discursive suggestion of original and universal assimilative colouration:—"We have seen that in all the instances to which I have referred, the external appearance of the animal bears definite relation to the appearance of the soil on which it lives, or the objects which surround it. It would appear as if there were a genius loci, whose subtle and pervading essence spread itself around, penetrating and impregnating the denizens of the place with its facies,—possibly only affecting some, the conditions of whose entry on existence render them more liable to receive its impression than others; more probably affecting all, some more and some less," &c.^[65] It may, however, be suggested that this adaptive colouration was due to an assimilative process in early times,^[66] and that the "genius loci" is a pseudonym of that operation. It is at least probable that where we have protective resemblance in a unicolorous condition, it is a survival of original assimilative colouration, and is not a direct product of "natural selection"; but is ratified and perpetuated by that agency as agreeing altogether with its conditions. Unchanged it has survived as the fittest.^[67] It must have been in the original head-quarters or centre of evolution before migration took place, and a uni- or concolorous hue prevailed. Such a centre for Anthropoids, palaeontology proves to have once existed in India. In the words of Mr. Lydekker:—"We have decisive proof that at a former epoch of the earth's history such an assembly of Primates was gathered together on the plains of India at a time when the Himalaya did not exist as has been seen nowhere else beyond the walls of a menagerie. Side by side with Langurs and Macaques closely resembling those now found in that region were Chimpanzees and Baboons as nearly related to those of modern Africa, whilst the extinct Indian Orang recalls the existing species of Borneo and Sumatra. India, therefore, in the Pliocene period, seems to have been the central point whence the main groups of Old World Primates dispersed themselves to their far distant homes."

 

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1. The action of the environment on fishes does not appear to be confined to colour alone, According to Prof. Seeley, "there are local races of many fishes which, under the changed conditions of physical geography, which from time to time affect the distribution of life on the earth, have become isolated from the rest of the race, so as to live on table-lands or low plains, in cold mountain lakes or in shallow swamps, in sluggish waters or rapid torrents, and thus, differently circumstanced, have developed into varieties distinguished by size, form, colour, and certain internal and external differences in the organs and proportions of the body" ('The Fresh-water Fishes of Europe,' p. 3). Leuciscus muticellus has all the fins "transparent and unspotted in Austrian specimens, but in examples from the Neckar the fins of the lower part of the body are yellow at the base, and this colour is occasionally seen in the dorsal and caudal. Bavarian fish have much black pigment in spots on the dorsal and caudal fins" (ibid. p. 173).
2. 'Curiosities Nat. Hist.,' pop. edit., 1st ser., pp. 235–7, 239.
3. Ibid. 4th ser., p. 271. This last conclusion seems scarcely borne out in a previous remark by the same naturalist that "white Trout prefer streams which contain bog water." ... " On the east side of Lough Corrib no white Trout are found—there is but very little bog water; but they are found on the west side, where the feeders of the lake run through a country abounding with bogs" (ibid. 4th ser., p. 253).
4. Jon. Couch, 'Hist. Fishes Brit. Islands,' vol. iv. p. 342.
5. A. Patterson. 'Zoologist,' 4th ser. vol. i. p. 557.
6. 'Audubon and his Journals,' vol. ii. p. 519.
7. 'Introd. Study Fishes,' p. 632.
8. Watson, 'Sketches of Brit. Sport. Fishes,' p. 77.
9. Lydekker, 'Roy. Nat. Hist.,' vol. v. pp. 412, 433.
10. 'Notes Nat. Hist. Strait of Magellan,' p. 42.
11. 'Entomologist,' vol. xxvi. p. 355. Mr. Wallace considers that the original colour of butterflies was a greyish or brownish neutral tint (' Darwinism,' p. 274); and the same opinion is held by Dr. Dixey in his study of the phylogeny of the Pierinæ ('Trans. Ent. Soc. Lond.,' 1894, p. 290).
12. Tutt, 'British Moths,' pp. 144, 149, 179, 305.
13. Miall, 'Nat. Hist. Aquat. Ins.,' p. 373.
14. 'Psyche,' vol. vii. p. 288.
15. 'Science,' 1893, p. 133.
16. 'Organic Evolution,' Eng. transl., p. 146. Sometimes we have records of environmental changes in the colours of insects without corresponding particulars being given. These are still suggestive. Thus Gerard states in the ' Dictionnaire d'Histoire naturelle ' of D'Orbigny (article "Espèce"), "that when the small brown Honey-bees from High Burgundy are transported into Bresse—although not very distant—they soon become larger, and assume a yellow colour; this happens even in the second generation" (cf. Varigny, ibid. p. 53). Again, M. d' Apchier de Pruns ('Revue Horticole,' 1883, p. 316) has recorded that "at Brasse les Mines, in Central France, white Oxen become of lighter hue, and Pheasants, Pigeons, Ducks, &c, have more or less white feathers; plants with variegated leaves soon become uniformly green"(cf. Varigny, ibid. p. 54).
17. 'The Great Sahara,' p. 214.
18. 'Cruise of the Marchesa,' 2nd edit., p. 84.
19. 'Lake Ngami,' p. 187.
20. 'Angola,' vol. ii. p. 75.
21. 'Cassell's Nat. Hist.,' vol. iii. p. 330. Dr. Sharpe has subsequently expressed further doubt on the suggested cause of this colouration: "The Touracous are birds which live in trees, and do not apparently descend to the ground, while the red feathers have been assumed by specimens in captivity, some of which moulted more than once " ('Roy. Nat. Hist.,' vol. iv. p. 13).
22. 'The Kilima-Njaro Expedition,' p. 65.
23. 'Across East African Glaciers,' p. 79.—Other travellers in South Africa have noticed an absence of game among ant-hills. Thus Andrew Steedman states: "We remarked that, where they most abounded, Antelopes and other species of gregarious animals were seldom to be met with " (' Wand, and Advent, in Int. S. Africa,' vol. i. p. 172).
24. 'The Sportsman in South Africa,' p. 46.
25. "The fundamental or ground colours of animals are, as has been shown in preceding chapters, very largely protective, and it is not improbable that the primitive colours of all animals were so. During the long course of animal development other modes of protection than concealment by harmony of colour arose, and thenceforth the normal development of colour due to the complex chemical and structural changes ever going on in the organism had full play; and the colours thus produced were again and again modified by natural selection for purposes of warning, recognition, mimicry, or special protection" ('Darwinism,' p. 288).
26. 'The Descent of Man,' 2nd edit., p. 464.
27. 'Cassell's Nat. Hist.,' vol. ii. p. 78.
28. 'Zoologist,' 4th ser. vol. ii. p. 163.
29. 'Roy. Nat. Hist.,' vol. i. pp. 443–4.
30. 'Wand, and Advent, in Int. S. Africa,' vol. i. p. 220.
31. A.R. Wallace, 'Darwinism,' p. 290.
32. Mcintosh and Masterman, 'Life-histories Brit. Marine Food Fishes,' p. 238.
33. Ibid. p. 33, fig. 8, and p. 281.
34. 'Roy. Nat. Hist.,' vol. v. p. 494.
35. Ibid. p. 497.
36. Cf. "Val. Address," 'Journ. Conch.,' April, 1888; and Boycott, 'Zoologist,' 3rd ser, vol. xx. p. 62.
37. 'Organic Evolution,' pp. 115–16.
38. 'Darwinism,' p. 289. Among the "Weasels (Mustelidæ), "there is a tendency for the different colours to arrange themselves in longitudinal lines or patches, so as to make the whole of the upper surface of the body light, and its under surface dark; and in no case are there either spots or transverse bands of colour, while equally noteworthy is the entire absence of alternating dark and light rings of colour in the tail" (Lydekker, 'Roy. Nat. Hist.,' vol. ii. p. 47).
39. 'Advent, in Mashonaland by two Hospital Nurses' (Col. Edit.), p. 277.
40. 'Geograph. and Geolog. Distrib. Animals,' p. 386. Prof. Boyd Dawkins likewise includes the "Spotted Hyena" (H. spelæa) in his list of mammalia occurring in Great Britain in association with Palaeolithic implements in the Pleistocene river deposits and the caves" ('Journ. Anthrop. Instit.,' vol. xviii. p. 243).
41. Huxley, 'Collected Essays,' vol. ii. p. 241.
42. "The origin of protective colours is to be sought in fortuitous variation preserved by selection" (Dr. Hart Merriam,—Balt. Meet. Am. Soc. Nat.,—vide 'Science,' new ser. vol. i. p. 38).
43. 'Narr. Explor. in Trop. S. Africa' (Minerva Lib. Edit.), p. 187.
44. 'Records of Sport in Southern India,' p. 41.
45. 'Roy. Nat. Hist.,' vol. ii. p. 855.—Livingstone seems inclined to the opinion that such animals take refuge in the forest to escape from the hunters: " But here, where they are killed by the arrows of the Balonda, they select for safety the densest forest, where the arrow cannot be easily shot" ('Missionary Travels and Researches in South Africa,' p. 280).
46. 'Zoologist,' 3rd ser., vol. xviii. p. 406.
47. 'Nature,' vol. l. p. 197.
48. 'Materials for the Study of Variation,' p. 266.
49. Ibid. p. 572.
50. Genesis, chap. xxx. verses 37–9. In the following chapter—xxxi. verses 10–13—this is altogether attributed to the favour of the God of Bethel.
51. 'The Great Sahara,' p. 61.
52. 'Colouration in Animals and Plants,' p. 23.
53. 'Colouration in Animals and Plants,' p. 92.
54. 'Livingstone's Last Journals,' vol. i. p. 95.
55. 'Emin Pasha in Central Africa,' p. 80.
56. 'Roy. Nat. Hist.,' vol. i. p. 501.
57. 'Anthropological Treatises,' Eng. transl. p. 191.
58. 'Descent of Man,' 2nd edit. p. 544.
59. Ibid. p. 546.
60. 'Darwinism,' pp. 199, 200.
61. Huxley, 'Collected Essays,' vol. ii. p. 426.
62. 'Wanderings,' Wood's edit. p. 94.
63. 'Curiosities of Natural History,' Pop. Edit., 3rd ser., p. 256.
64. 'Organic Evolution,' Eng. transl. p. 57.
65. "Disguises in Nature," vide 'Edinburgh New Philosoph. Journ.,' January, 1860.
66. Eimer proposes a theory of colour-photography: "The colours of the environment of an animal may be reflected in the colours of its skin" ('Organic Evolution,' Eng. transl. p. 145).
67. A different argument, propounded on somewhat similar grounds, was advanced by Agassiz in his "Natural Relations between Animals and the Elements in which they live," to prove that marine animals were less specialised in structure than those inhabiting the land areas (vide Silliman's 'Amer. Journ. Sci. and Arts,' May, 1850).