CHAPTER VI

THE COLOURATION OF ORGANISMS

The theory of protective colouration has been carried to absurd

lengths—It will not bear close scrutiny—Cryptic colouring—Sematic

colours—Pseudo-sematic colours—Batesian and Müllerian

mimicry—Conditions necessary for mimicry—Examples—Recognition

markings—The theory of obliterative colouration—Criticism of the

theory—Objections to the theory of cryptic colouring—Whiteness of the

Arctic fauna is exaggerated—Illustrative tables—Pelagic

organisms—Objectors to the Neo-Darwinian theories of colouration are to

be found among field naturalists—G. A. B. Dewar, Gadow, Robinson, F. C.

Selous quoted—Colours of birds’ eggs—Warning colouration—Objections to

the theory—Eisig’s theory—So-called intimidating attitudes of

animals—Mimicry—The case for the theory—The case against the

theory—“False mimicry”—Theory of recognition colours—The theory

refuted—Colours of flowers and fruits—Neo-Darwinian

explanations—Objections—Kay Robinson’s theory—Conclusion that

Neo-Darwinian theories are untenable—Some suggestions regarding the

colouration of animals—Through the diversity of colouring of organisms

something like order runs—The connection between biological molecules

and colour—Tylor on colour patterns in animals—Bonhote’s theory of

pœcilomeres—Summary of conclusions arrived at.

Since the publication of _The Origin of Species_, naturalists have paid

much attention to the colouration of animals and plants, with the result

that a large majority of scientific men to-day hold the belief that all,

or nearly all, the colours displayed by animals are of direct utility to

them, and are therefore the direct result of natural selection; a few

would add, “and of sexual selection.”

“Among the numerous applications of the Darwinian theory,” writes

Wallace, “in the interpretation of the complex phenomena, none have been

more successful than those which deal with the colours of animals and

plants.”

Robinson on Protective Colouring

We readily admit that the Darwinian theory has thrown a great deal of

light on the phenomenon of animal colouration; it has reduced to

something like order what was before Darwin’s time chaos. While admitting

this we feel constrained to say that many naturalists, especially Dr

Wallace and Professor Poulton, have pushed the various theories of animal

colouration to absurd lengths. As Dr H. Robinson truly says (_Knowledge_,

January 1909), “It seems to have been taken for granted, and some even of

Dr Wallace’s writings may be interpreted in this sense, that protective

colouring is necessary to the continued existence of every species, and

that, sexual colouration apart, it is incumbent on naturalists to offer

ingenious speculations in this sense to account for the appearance even

of the most bizarre and conspicuous beasts. Thence it has been but a

short step to the announcement of those speculations as further evidence

in favour of natural selection, and of various assumptions made in the

speculative process as indisputable facts.”

The result of this is that men have ceased to regard the Neo-Darwinian[6]

theories of protective colouration, mimicry, and recognition markings as

mere hypotheses which seem to throw light on certain phenomena in the

organic world. These theories have assumed the rank of laws of nature. To

dispute them would seem to be as futile as to assert that the earth is

flat. To take exception to them would appear to be as ridiculous as to

object to Mont Blanc. To dare to criticise them is heresy of the worst

type.

Be this as it may, scientific dogma or no scientific dogma, scientific

opinion or no scientific opinion, we have dared to weigh these theories

in the balance of observation and reason, and have found them wanting. We

have examined these mighty images of gold, and silver, and brass, and

iron, and found that there is much clay in the feet.

We shall devote this chapter to lifting the hem of the garment of

sanctity that envelopes each of these images, and so expose to view the

clay that lies concealed.

We propose, first, to set forth in outline what we trust will be

considered a fair statement of the various theories of animal colouration

which are generally accepted to-day, then to show up the various weak

points in these, and lastly, to endeavour to ascertain whether there are

not some alternative explanations in certain cases to which the

generally-accepted theory does not apply.

Cryptic Colouring

Neo-Darwinians divide the various forms of colouration into three great

classes:—(1) Cryptic colouring, or protective and aggressive

resemblances; (2) sematic colours, or warning and recognition colours;

and (3) pseudo-sematic colours, or mimicry. A tabular statement of this

scheme of colouring will be found on pp. 293-7 Professor Poulton’s

_Essays on Evolution_.

As regards class (1), Neo-Darwinians point out that the great majority of

animals are so coloured as to make them very difficult to see in their

natural environment, hence the whiteness of the creatures which inhabit

the snow-bound Arctic regions, the sandy colour of desert animals, the

spotted coats of creatures which live among trees, the striped markings

of animals which spend their lives amid long grass, and the transparent

blueness of pelagic animals. The theory is that all kinds of animals,

whether those that hunt or those that are hunted, derive much advantage

from being coloured like their environment. The hunted creatures are

thereby the better able to elude the vigilance of their foes, while those

that hunt are in a position to take their quarry by surprise; so that

natural selection has caused them all to assimilate to the hues of their

surroundings. Neo-Darwinians point to the fact that some Arctic animals

are brown in the summer to match the ground from which the snow has

melted, and turn white in winter to assimilate with their snowy

background. Naturalists further cite, as evidence in favour of this

theory, the case of those creatures which imitate inanimate objects, such

as leaves and twigs, and thereby escape the observation of their foes.

Thus, the great majority of animals are supposed to be cryptically

coloured, that is to say, coloured so as to be, if not quite invisible,

at least very inconspicuous in their natural habitat.

Warning Colouration

It is, however, generally admitted that many creatures are not

cryptically coloured. Some, indeed, seem to be coloured in such a way as

to render them as conspicuous as possible. The Neo-Darwinians declare

that there is a reason for this. “If,” writes Professor Milnes Marshall

(page 133 of his _Lectures on the Darwinian Theory_), “an animal,

belonging to a group liable to be eaten by others, is possessed of a

nauseous taste, or if an animal, such as a wasp, is specially armed and

venomous, it is to its advantage that it should be recognised quickly,

and so avoided by animals that might be disposed to take it as food.

“Hence arises warning colouration, the explanation of which is due to

Wallace. Darwin, who was unable to explain the reason for the gaudy

colouration of some caterpillars, stated his difficulty to Wallace, and

asked for suggestions. Wallace thought the matter over, considered all

known cases, and then ventured to predict that birds and other enemies

would be found to refuse such caterpillars if offered to them. This

explanation, first applied to caterpillars, soon extended to adult forms,

not only of insects, but of other groups as well. . . . Insects afford

many admirable examples of warning colours, and many well-known instances

occur among butterflies. The best examples of these are found in three

great families of butterflies—the _Heliconidæ_, found in South America,

the _Danaidæ_, found in Asia and tropical regions generally, and the

_Acræidæ_ of Africa. These have large but rather weak wings, and fly

slowly. They are always very abundant, all have conspicuous colours or

markings, and often a peculiar form of flight, characters by which they

can be recognised at a glance. The colours are nearly always the same on

both upper and under surfaces of the wings; they never try to conceal

themselves, but rest on the upper surfaces of leaves and flowers.

Moreover, they all have juices which exhale a powerful scent; so that, if

they are killed by pinching the body, a liquid exudes which stains the

fingers yellow, and leaves an odour which can only be removed by repeated

washing. This odour is not very offensive to man, but has been shown by

experiment to be so to birds and other insect-eating animals.

“Warning colours are advertisements, often highly coloured

advertisements, of unsuitability as food. Insects are of two kinds—those

which are extremely difficult to find, and those which are rendered

prominent through startling colours and conspicuous attitudes. Warning

colours may usually be distinguished by being conspicuously exposed when

the animal is at rest. Crude patterns and startling contrasts in colour

are characteristically warning, and these colours and patterns often

resemble each other; black combined with white, yellow, or red, are the

commonest combinations, and the patterns usually consist of rings,

stripes, or spots.”

We trust that we shall be forgiven for this lengthy quotation. Our object

in reproducing so large an extract is to allow the Neo-Darwinians to

speak for themselves. Were we to state their theory in our own words, we

might perhaps be charged with stating it inaccurately. We should add

that, even as natural selection is supposed to have been the cause of

conspicuous colouring in some organisms, so has it caused others to

assume intimidating attitudes or emit warning sounds, such as a hiss,

when attacked.

Batesian Mimicry

We now come to the third great class of animal colours—mimetic colours.

Mimicry is of two kinds, known respectively as Batesian and Müllerian

mimicry, after their respective discoverers.

It has been found that some apparently warningly coloured butterflies and

other creatures are palatable to insectivorous animals. The explanation

given of this is that these showy but edible butterflies “mimic,” that is

to say, have the appearance of, show a general resemblance to, species

which are unpalatable. This is known as Batesian mimicry. “Protective

mimicry,” writes Professor Poulton (_Essays on Evolution_, p. 361), “is

here defined as an advantageous superficial resemblance of a palatable

defenceless form to another that is specially defended so as to be

disliked or feared by the majority of enemies of the groups to which both

mimic and model belong—a resemblance which appeals to the senses of

animal enemies . . . but does not extend to deep-seated characters,

except when the superficial likeness is affected thereby.”

As Wallace has pointed out, five conditions must be satisfied before such

protective mimicry can occur:—

“1. That the imitative species occur in the same area and occupy the same

station as the imitated. 2. That the imitators are always the more

defenceless. 3. That the imitators are always less numerous in

individuals. 4. That the imitators differ from the bulk of their allies.

5. That the imitation, however minute, is external and visible only,

never extending to internal characters or to such as does not affect the

external characters.” (_Darwinism_, Chap. ix.)

Thus the mimic is supposed to deceive his enemies by deluding them into

the belief that he is the inedible species which they once tried to eat

and vowed never again to touch, so nasty was it. The mimic, then, may be

compared to the ass in the lion’s skin. Needless to say, this mimicry is

quite unconscious. It is supposed to have been developed by natural

selection. Every popular book on Evolution cites many examples of such

mimicry. We may therefore content ourselves with mentioning but a few.

Examples of Mimicry

Our common wasps are copied by a beetle (_Clytus arietis_), active in

movement and banded black and yellow, and by several yellow-barred

hover-flies (_Syrphidæ_); and the bumble-bee by a clear-winged moth

(_Sesia fuciformis_). There is, indeed, a whole group of these

clear-winged moths, resembling bees, wasps, and other stinging

hymenoptera. The common Indian Danaid butterfly, _Danais chrysippus_, is

marvellously reproduced by the female of _Hypolimnas misippus_, a form

allied to our Purple Emperor. The male of this is black, with white

blue-bordered patches, the female chestnut, edged with black and with

white spots at the tips of the wings, as in the _Danais_. Finn has shown

experimentally that this species is liked by birds.

Another common Indian Danaid (_D. limniace_), black, spotted with pale

green, is imitated, though not very closely, by the female of one of the

“white” group, _Nepheronia hippia_. Finn found that this insect was eaten

freely by birds, and that the common jungle-babbler (_Crateropus

canorus_) was deceived by the mimicry of the female. The very nauseous

Indian swallow-tail (_Papilio aristolochiæ_) is closely imitated by

another swallow-tail (_P. polites_), both having black wings marked with

red and white; _P. aristolochiæ_, however, has a red abdomen. This

difference was not noticed by two species of Drongo-shrikes (_Dicrurus

ater_ and _Dissemurus paradiseus_), to which the butterflies were

offered; but the Pekin robin (_Liothrix luteus_)—a very intelligent

little bird—did not fail to pick out and eat the mimic, though it was

deceived by the marvellously perfect imitation of _Danais chrysippus_, by

the female of the _Hypolimnas_.

Such resemblances can therefore be effective.

The cases of mimicry usually quoted include very few among mammals,

probably, as Beddard suggests, because the species of that class are

relatively few.

The insectivorous genus _Tupaia_ is supposed to mimic the squirrels,

which it much resembles as regards form in all respects save the long

muzzle; the idea being that squirrels are so active that carnivorous

animals find it hopeless to pursue them.

On the other hand, there is a squirrel (_Rhinosciurus tupaioides_) which

is supposed to mimic the tupaias! It has a similar long muzzle, and the

light shoulder-stripe which is a common marking in tupaias. But why the

squirrel, one of the group imitated, should in turn become an imitator is

not explained.

The true interpretation of the resemblance is probably that both

squirrels and tupaias are adapted to a life in trees. Like profession

begets like appearance: the ground-living shrews much resemble mice, and

the moles find representatives in mole-like rodents.

Another case, however, wherein true mimicry may have come into play is

that of the South American deer (_Cervus paludosus_) which singularly

resembles in colouration the long-legged wolf or _Aguara-guazu_ (_Canis

jubatus_). Both these species are chestnut in colour, with the front of

the legs black, and the ears lined with white hair; both inhabit the same

regions in South America.

Müllerian Mimicry

The second kind of mimicry—Müllerian mimicry—is where one unpalatable

creature resembles another. This form of mimicry is named after Fritz

Müller, who suggested the explanation now usually accepted, namely, that

“Life is saved by a resemblance between the warning colours in any area,

inasmuch as the education of young inexperienced enemies is facilitated,

and insect life saved in the process.” “It is obvious,” writes Poulton

(p. 328 of _Essays on Evolution_), “that the amount of learning and

remembering, and consequently of injury and loss of life involved in

these processes, are reduced when many species in one place possess the

same aposematic colouring, instead of each exhibiting a different danger

signal. . . . The precise statement of advantage was made by Mr Blakiston

and Mr Alexander, of Tokio. ‘Let there be two species of insects equally

distasteful to young birds, and let it be supposed that the birds would

destroy the same number of individuals of each before they were educated

to avoid them. Then if these insects are thoroughly mixed and become

undistinguishable to the birds, a proportionate advantage accrues to each

over its former state of existence. These proportionate advantages are

inversely in the duplicate ratio of the respective percentages that would

have survived without the mimicry.’”

This is rather a cumbrous method of saying that if there are in a

locality a number of young birds, and each of these has to learn by

experience which insects are edible and which are not, each will, if it

learns by one example, devour one insect of any given pattern. Now, if

two species of inedible insects have this pattern, they will between them

lose only one member in the educating process of each bird, whereas if

each species of insect had a colouration peculiar to itself, each species

would lose a whole individual instead of half a one. There can be no

doubt that such a livery of unpalatability is of some advantage to its

possessors.

It has been shown experimentally that hand-reared young birds have to

acquire their knowledge of flavours and colours by experiment.

It is well known that in many species the male and the female are not

coloured alike. Such species are said to exhibit sexual dimorphism. In

these cases it is usually the male that is more conspicuously coloured.

Darwin felt that the theory of natural selection could not satisfactorily

account for this phenomenon, so put forward the supplementary theory of

sexual selection. On this hypothesis the females are supposed to be able

to pick and choose their mates, and to select the most beautiful and

ornamental ones, hence the greater showiness of these in most sexually

dimorphic species. Wallace does not accept this theory. He thinks it

unnecessary. He looks upon the brilliant colouring of the males as due to

their superior vigour; moreover, he says that it is the hen that sits

upon the eggs, and so requires a greater degree of protection than the

male, and therefore natural selection has not permitted her to develop

all the ornaments displayed by the cock. With the phenomenon of sexual

dimorphism we shall deal at length in the next chapter.

Danger Signals

Dr Wallace recognizes yet another exception to the rule that animals are

cryptically coloured. Many creatures possess on the body markings which

tend to render them conspicuous rather than difficult to see. Where such

markings occur on gregarious animals, Wallace believes that they have

been evolved by natural selection, either to enable their possessors to

recognize one another, or to act as a danger signal to their fellows. The

white tail of the rabbit is believed by Wallace to serve as a danger

signal. The first member of the company to espy the approaching foe takes

to his heels, and, as he moves, his white tail catches the eye of his

neighbour, who at once follows him, so that, in less time than it takes

to tell, the whole company of rabbits is scampering towards the burrow,

thanks to the white under-surface of the tail.

Even as Wallace out-Darwin’s Darwin, so does Mr Abbott Thayer, an

American naturalist and artist, out-Wallace Wallace. That gentleman seems

to be of opinion that _all_ animals are cryptically or, as he calls it,

concealingly or obliteratively coloured. Even those schemes of colour

which have hitherto been called conspicuous are, he asserts, “purely and

potently concealing” when looked at properly, that is to say, with the

eye of the artist.

Lest it be thought unnecessary to criticize a hypothesis which appears to

be based upon the assumption that animals see with the eye of the artist,

we may say that Professor Poulton writes approvingly of Thayer’s theory.

He frequently alludes to it in his _Essays on Evolution_, and he

published an account of it in the issue of _Nature_, dated April 24,

1902. Moreover the hypothesis has been enunciated in such scientific

journals as _The Auk_ (1896) and _The Year-Book of the Smithsonian

Institution_ (1897).

Thayer asserts that all animals, or at any rate the great majority,

including many that are usually supposed to be conspicuously coloured,

are in reality obliteratively coloured—that is to say, coloured in such a

way that the effects of light and shade are completely counteracted, with

the result that they are invisible.

Obliterative Colouring

It is possible, says Mr Thayer, to almost obliterate a statue in a

diffused light, by putting white paint on the surfaces in darkest shadow

and dark paint on the most brightly lighted parts, all in due proportion.

Now this is precisely what nature is supposed by Mr Thayer to have done

for all her creatures.

It is well known that a great many animals, as for example the Indian

black-buck and the hare, are coloured on the upper side and white below.

This is called by Mr Thayer the principle of the gradation of colour. It

runs, he declares, all through the animal world, and is “the main

essential step toward making animals inconspicuous under the descending

light of the sky.”

Animals, he contends, are not protectively coloured to look like clods or

stumps or like surrounding objects, they are simply obliteratively

coloured—coated, as it were, with invisible paint.

To quote from _The Century Magazine_ (1908): “Whales, lions, wolves,

deer, hares, mice; partridges, quails, sandpipers, larks, sparrows;

frogs, snakes, fishes, lizards, crabs; grasshoppers, slugs,

caterpillars—all these animals, and many thousands more, crawl, crouch,

and swim about their business, hunting and eluding, under cover of this

strange obliterative mask, the smooth and perfect balance between shades

of colour and degrees of illumination.”

Nature having thus visually unsubstantialized the bodies of animals, so

that, if seen at all, they look flat and ghostly, does not stop there.

From solid-shaded bodies they have been converted, as it were, into flat

cards or canvases, and, to complete the illusion of obliteration,

pictures of the background—veritable pictures of the more or less distant

landscape—have been painted on their canvases! Such in effect are the

elaborate “markings of field and forest birds.”

Again he writes: “Brilliantly changeable or metallic colours are usually

supposed to make the birds that wear them conspicuous, but nothing could

be further from the truth. Iridescence is, indeed, one of the strongest

factors of concealment. The quicksilver-like intershifting of many lights

and colours, which the slightest motion generates on an iridescent

surface, like the back of a bird or the wing of a butterfly, destroys the

visibility of that wing or back as such and causes it to blend

inextricably with the gleaming and scintillating labyrinthine-shadowed

world of wind-swayed leaves and flowers.”

According to Thayer, the skunk, which for years has been an important

item of the stock-in-trade of the advocates of the theory of warning

colouration, is an excellent example of obliterative colouring, since its

enemies are supposed to mistake for the sky-line the line of junction

between the white fur of the back and the dark fur of the sides.

Similarly the crocodiles are supposed to mistake a flamingo for the sky

at sunrise or at sunset!

There is doubtless something in this theory of obliterative colouration.

Any one can see, by paying a visit to the South Kensington Museum, that

an animal which is of a lighter colour below than above, is less

conspicuous in a poor light than it would be were it uniformly coloured.

There is then no doubt that this scheme of colour, which is so common in

nature, has some protective value.

To this extent has Mr Thayer made a valuable contribution to zoological

science. But when he informs us that obliterative colouring is a

“universal attribute of animal life,” we feel sorely tempted to poke fun

at him.

We would ask all those who believe in the universality of obliterative

colouring to observe a flock of rooks wending their way to their

dormitories at sunset.

Let us now pass on to the examination of the more orthodox theories of

animal colouration.

Objections to the Theory of Cryptic Colouring

Before criticising the theory of cryptic colouring, we desire to state

distinctly that we admit that, where other things are equal, it is of

advantage to all creatures which hunt or which are preyed upon to be

inconspicuous. If difficult to distinguish amid their natural

surroundings, the former are likely to secure their prey readily, and the

latter have a chance of escaping from their enemies. Our quarrel is with

the theory of cryptic colouring as it is enunciated by many

Neo-Darwinians, with the theory that every hue, every marking, every

device displayed by an organism is of utility to the organism and has

been directly developed by natural selection.

The extreme advocates of the theory of cryptic colouring have greatly

exaggerated the degree in which animals are assimilated to their natural

environment.

Fauna of Polar Regions

We grant that a great many creatures, which when seen in a menagerie

appear very conspicuous, are the reverse of conspicuous when standing

motionless amid their natural surroundings. As Beddard has pointed out,

it is often not easy to find a sixpenny piece which has been dropped on

the carpet, but the reason for this is, not that the coin is protectively

coloured, but that any small object, no matter how coloured, is difficult

to distinguish amid a variegated environment. The assumption of a white

winter coat by many organisms that live in northern latitudes has been

cited, again and again, as showing how important it is for an animal to

be protectively coloured. If, it is urged, those creatures that live in

lands which are covered in snow for half of the year have become white in

winter by the action of natural selection in order to escape their foes,

it is obviously of paramount importance to all creatures that they should

be cryptically coloured. Popular books on natural history convey the

impression that during winter the snow-clad, ice-bound Arctic regions are

peopled by a fauna whose fur or hair rivals in whiteness the snowy mantle

of the earth. The impression thus conveyed is misleading. It is true that

an unusually large percentage of the animals that inhabit the polar

regions are white in winter, but the majority of the creatures which

dwell there do not assume the white garb of winter.

As the fauna of the polar regions is a small one, we are able to give

lists of all the birds and mammals which dwell in the Arctic and the

Antarctic regions. We have arranged these in in three columns. In the

first are placed those creatures which are white throughout the year, in

the third those that retain their colour through the winter, while the

middle column contains those forms which change their colouring with the

season.

ARCTIC FAUNA.

Mammals.

White.

Polar Bear.

Arctic Fox (some individuals).

White Whale or Beluga.

Changing with the Seasons.

Arctic Fox (most individuals).

Arctic Lemming.

Stoat.

Weasel.

Blue Hare.

Coloured.

Arctic Fox (sometimes).

Reindeer.

Musk-ox.

Glutton.

Moose.

Sable.

Seals.

Walrus.

Narhwal.

Greenland Whale.

Birds.

White.

Ivory Gull.

Snowy Owl.

Gyrfalcon.

Snow Goose.

Changing with the Seasons.

Black Guillemot.

Ptarmigans.

Snow Bunting (whitest in summer!)

Razorbill.

Little Auk (throat only becomes white).

Coloured.

Sea Eagle.

Greenland Redpoll (very pale).

All Arctic Geese and Ducks other than Snow Goose.

Raven.

Cormorant.

Brunnich’s Guillemot.

Puffin.

Fulmar Petrel.

Ross’s Gull.

Glaucous Gull (very pale).

Sandpipers.

ANTARCTIC FAUNA.

Mammals.

White.

Antarctic White Seal (_Lobodon carcinophaga_), in some cases.

Changing with the Seasons.

None.

Coloured.

Other Seals than _Lobodon._

Whales.

Birds.

White.

Sheathbill.

Snowy Petrel.

Giant Petrel (some individuals).

Chick of Emperor Penguin.

Changing with the Seasons.

None.

Coloured.

Penguins.

Cormorant.

Skua Gull.

Giant Petrel (usually).

Other Petrels.

It will be observed that the third column contains the largest number of

forms. It is thus evident that the whiteness of the Arctic and Antarctic

faunas in winter has been greatly exaggerated.

The Arctic fox appears in all three columns, as the creature seems to

fall into three races—a permanently white race, a permanently coloured

race, and a seasonally dimorphic race.

Of the creatures set forth in the middle column of the above tables all

are whiter in winter than in summer with the exception of the snow

bunting, who sets at naught the theory of cryptic colouring by turning

darker in winter! The same may be said of the Alpine chamois.

The advocates of the theory of protective colouring assert that the

creatures which do not turn white in winter are strong and active animals

which have no enemies to fear.

This contention is met by F. C. Selous as follows (_African Nature Notes

and Reminiscences_, p. 9): “According to the experience of Arctic

travellers, large numbers of young musk oxen are annually killed by

wolves. . . . Nothing, I think, is more certain than that a far smaller

percentage of so-called protectively coloured giraffes are killed

annually by lions in Africa than of musk oxen by wolves in Arctic

America.”

Another difficulty which confronts the Neo-Wallaceian school is that, _ex

hypothesi_, the assumption of the white coat was gradual. Hence the

change in the direction of whiteness cannot, in its first beginning, have

been of perceptible utility to an organism. How then can natural

selection have operated on it?

Pelagic Organisms

The transparency of pelagic organisms is frequently cited as exemplifying

cryptic colouring. We all know that the common jelly-fish is as

transparent as glass. Floating on the surface of the ocean are millions

of tiny organisms, so transparent as to be invisible to the human eye. At

first sight this certainly appears to be a remarkable case of protective

colouring. Unfortunately, nearly all the more highly developed forms

display conspicuous pigment (as in most jelly-fish) in some part of the

body.

“An animal floating about in the sea,” writes Beddard, “perfectly

transparent, but decked with dense black patches, of the size of saucers,

would betray its whereabouts even to the least observant; if the observer

were stimulated by hunger or fear, the conspicuousness would not be

lessened. . . . Besides the internecine warfare which is continually

going on amongst the smaller surface organisms, they are devoured

wholesale by the larger pelagic fish, and by whales and other Cetacea. A

whale, rushing through the water with open mouth and gulping down all

before him, is not the least inconvenienced by the invisibility of the

organisms devoured in such enormous quantities; nor do a solid phalanx of

herring or mackerel stop to look carefully for their food: they take what

comes in their way, and get plenty in spite of ‘protective absence of

colouration.’

“If the transparency of the pelagic organisms be due entirely to natural

selection, it is remarkable that there is so little modification in this

direction among the species inhabiting the bottom at such depths as are

accessible to the sun’s rays; the advantage gained by this transparency

and consequent invisibility would be equally great. And yet this is not

the case; the bulk of the bottom fauna of the coasts are brilliantly

coloured animals, and those that show any protective colouring at all

appear to be coloured so as to resemble stones or sea-weeds.”[7]

Before leaving the subject of marine animals, we may point out that the

majority of the creatures that live in the everlasting blackness of the

depths of the ocean display exceedingly conspicuous colouring, and this

colouring seems to be constant. In such cases the colouring cannot be

useful as such to its possessors. The same may be said of the colour of

blood, or of the colouring of the internal tissues of all organisms. We

must not lose sight of the fact that every organism, and every component

part thereof, must of necessity be either of some colour or perfectly

transparent. It seems to us that since the appearance of _The Origin of

Species_ zoologists have tended to exaggerate the importance of colouring

to organisms; they frequently speak of it as though it were the one and

only factor in the struggle for existence. It is on this account that

they feel it incumbent upon them to find ingenious explanations for every

piece of colouring displayed by every plant or animal.

Unimportance of Colour

The tendency to exaggerate the importance to an animal of its colouring

is doubtless in large part due to the fact that many zoologists are

content to study nature in museums rather than in the open. Some of those

who observe organisms in their natural surroundings, especially in such

favourable localities as the tropics, seem to be of opinion that natural

selection has but little influence on the colouration of organisms.

Thus D. Dewar writes (_Albany Review_, 1907): “Eight years of

bird-watching in India have convinced me that, so far as the struggle for

existence is concerned, it matters not to a bird whether it be

conspicuously or inconspicuously coloured, that it is not the necessity

for protection against raptorial foes which determines the colouring of a

species; in short, that the theory of protective colouration has but

little application to the fowls of the air.”

Similarly, F. C. Selous writes, on page 13 of _African Nature Notes and

Reminiscences_: “Having spent many years of my life in the constant

pursuit of African game, I have certainly been afforded opportunities

such as have been enjoyed by but few civilised men of becoming intimately

acquainted with the habits and life-history of many species of animals

living in that continent, and all that I have learned during my long

experience as a hunter compels me to doubt the correctness of the now

very generally accepted theories that all the wonderfully diversified

colours of animals—the stripes of the zebra, the blotched coat of the

giraffe, the spots of the bushbuck, the white face and the rump of the

bontebok, to mention only a few—have been coloured either as means of

protection from enemies or for the purpose of mutual recognition by

animals of the same species in times of sudden alarm.”

So also G. A. B. Dewar—a very close observer of nature in England—writes,

in _The Faery Year_: “Few theories in natural history have received more

attention of late years than protective or aggressive colour, ‘mimicry,’

and harmony with environment. . . . To doubt this use of colour to

animals seems like inviting back chaos in place of cosmos—for abandon the

theory, and a world of colour is straightway void of purpose, a muddle of

chance. So we all like the theory. Some, however, perceive plans to aid

the wearer in every colour, tint, shade, and pattern. We may be sceptical

of a good many of the cases they cite in support of colour aid, though

attracted by the main idea.”

Writing of the commoner British butterflies, he says: “After a little

practice, any man furnished with good eyesight can easily distinguish

these butterflies—blues, coppers, small heaths, and meadow browns—from

their perches; and so we may be sure that the small beast, bird, or

insect of prey, with sense of colour or form, could also distinguish

them. . . . Quite often, without even searching for them, I can see

cabbage whites and other butterflies asleep on perches to which they by

no means assimilate.” Mr G. A. B. Dewar suggests that the safety of the

resting butterfly lies in “the position, the couch on high, . . . not the

mask of colour or marking.”

Gadow on Coral Snakes

Two short visits to Southern Mexico sufficed to show Dr Hans Gadow that

some of the commonly accepted explanations of colour phenomena are not

the correct ones.

Thus writing of coral snakes, he says, on page 95 of _Through Southern

Mexico_: “They are usually paraded as glaring instances of warning

colouration, but I am not at all sure whether this is justifiable.

Certainly these _Elaps_ are most conspicuous and beautiful objects. Black

and carmine or coral red, in alternate rings, are the favourite pattern;

sometimes with narrow golden-yellow rings between them, as if to enhance

the beautiful combination. But these snakes are inclined to be nocturnal

in their habits, and, except when basking, spend most of their time under

rotten stumps, in mouldy ground, or in ants’ nests in search of their

prey, which must be very small, to judge from the size of the mouth.”

Dr Gadow goes on to show that although black and red are very strong

contrasts in the day-time, the combination ceases to be effective in the

dark. He suggests that red and black is a self-effacing rather than a

warning pattern. He further points out that several kinds of harmless

snakes have the same colouring and pattern. “There seems,” he says, “to

be no reason why we should not call these cases of mimicry; and yet this

is most likely a wrong interpretation, since such harmless snakes are

also found in districts where the _Elaps_ does not occur, not only in

Mexico, but likewise in far-distant parts of the world, where neither

elapines nor any other similarly coloured poisonous snakes exist. To

interpret this as an instance of ‘warning colours’ in a perfectly

harmless snake, which has no chance of mimicry, amounts in such cases to

nonsense, and we have to look for a different explanation upon

physiological and other grounds.”

It is, to say the least of it, significant that all the opposition to the

theory of protective colouration comes from those who observe nature

first hand, while the warmest supporters of the theory are cabinet

naturalists and museum zoologists.

In the case of nocturnal creatures, as Dr H. Robinson very sagely points

out (_Knowledge_, January 1909), the value for protective purposes of any

given colouration must depend very largely on the state of the moon. “It

was,” he writes, “a common experience in the South African War that on

overcast or moonless nights the nearly black army great-coat made a

picquet sentry invisible at a distance of a few feet. In strong moonlight

this garb could be seen at a great distance, whereas a khaki pea jacket,

useless on a dark night, answered the requirements of invisibility very

well.” It is thus evident that the dark colour of the buffalo and sable

antelope cannot be protective on both dark and moonlight nights.

The theory of protective colouration is based on the tacit assumption

that beasts of prey rely on eyesight for finding their quarry. Raptorial

birds certainly do use their eyes as the means of discovering their

victims; but the great majority of predaceous mammals trust almost

entirely to their power of smell as a means for tracking down their prey.

F. C. Selous Quoted

“Nothing,” writes F. C. Selous, on page 14 of _African Nature Notes and

Reminiscences_, “is more certain than that all carnivorous animals hunt

almost entirely by scent until they have closely approached their quarry,

and usually by night, when all the animals on which they prey must look

very much alike as far as colour is concerned.”

The herbivora—the quarry for the beast of prey—too, have a keen sense of

smell, so that they trust their noses rather than their eyes for safety.

No observer of nature can have failed to remark how the least movement on

the part of an animal will betray its whereabouts, even though in

colouring it assimilates very closely to the environment. So long as the

hare squats motionless in the furrow, it may remain unobserved, even

though the sportsman be searching for it; but the least movement on its

part at once attracts his eye. Thus, in order that protective colouration

can be of use to its possessor, the latter must remain perfectly

motionless. But, in tropical countries, where flies, gnats, etc., are a

perfect scourge, no large animal is, when awake, motionless for ten

seconds at a time. The tail is in constant motion, flicking off the flies

that attempt to settle on the quadruped. The ears are used in a similar

manner. Thus the so-called protective colouring of herbivora cannot

afford them much protection. It is further worthy of note that the

brush-like tip to the tail of many mammals is not of the same colour as

the skin or fur. It is very frequently black. Thus we have the spectacle

of a protectively coloured creature continually moving, as if to attract

attention, almost the only part of its body that is not protectively

coloured!

Sexual Dimorphism

Many species of birds display what is known as seasonal dimorphism, still

more display sexual dimorphism.

Seasonally dimorphic birds very often assume a bright livery at the

breeding season; this nuptial plumage is by no means invariably confined

to the cock, so that we are brought face to face with the fact that some

hen birds, that are normally inconspicuously coloured, become showy and

easy to see at the nesting time, that is to say, precisely at the season

when they would seem to be most in need of protection.

In the great majority of cases of sexual dimorphism among birds the cock

is the more showily coloured. Now, if it be a matter of life-and-death

importance to a bird to be protectively coloured, we should expect the

showily coloured cock birds to be far less numerous than the

dull-plumaged hens, since the former are, _ex hypothesi_, exposed to far

greater danger than the inconspicuous hens. As a matter of fact, cock

birds in practically all species appear to be at least as numerous as the

hens. Nor can it be said that this is due to their more secretive habits.

As a general rule, cock birds show themselves as readily as the hens;

indeed, in the case of the familiar blackbird, the conspicuous cock is

less retiring in his habits than the more sombre hen. It may, perhaps, be

thought that the greater danger to which the sitting bird is exposed

accounts for the fact that hens, notwithstanding their protective

colouration, are not more numerous than the cocks. Unfortunately for the

supposition, in many sexually dimorphic hens, as, for example, the

paradise fly-catcher (_Terpsiphone paradisi_), the showy cock shares the

burden of incubation equally with the hen.

It frequently happens that allied species of birds are found in

neighbouring countries. The Indian robins, for example, fall into two

species. The brown-backed robin (_Thamnobia cambayensis_) occurs north of

Bombay, while the black-backed species (_T. fulicata_) is found south of

Bombay. The hens of these two species are almost indistinguishable, but

the cocks differ, in that one has a brown back, while the other’s back is

glossy black. The Wallaceian theory of colouration seems quite unable to

explain this phenomenon—the splitting up of a genus into local

species—which is continually met with in nature. Equally inimical to the

theory of protective colouration is the existence, side by side, of

species which obtain their living in much the same manner. On every

Indian lake three different species of kingfisher pursue their profession

cheek by jowl; one of these—_Ceryle rudis_—is speckled black and white,

like a Hamburg fowl; the second is the kingfisher we know in England; and

the third is the magnificent white-breasted species—_Halcyon

smyrnensis_—a bright-blue bird with a reddish head and a white wing bar.

It is obvious that all three of these diversely plumaged species cannot

be protectively coloured. It may perhaps be objected that the piscatorial

methods of these kingfishers differ in detail. We admit that this is the

case, but would maintain, at the same time, that these comparatively

slight differences in habit do not account for the very striking

differences in plumage. We may also cite the yellow and pied wagtails of

our own country, which may be seen feeding in the same meadows. Most

familiar and striking of all is the everyday sight of a blackbird and

thrush plying their respective avocations within a few yards of each

other on the same lawn, differently coloured though they be.

Another weighty objection to the generally accepted theory of protective

colouration is that some of the creatures which assimilate most closely

to their environment are those which appear to be the least in need of

such protection.

Precis Artexia

The butterfly _Precis artexia_, writes F. C. Selous, “is only found in

shady forests, is seldom seen flying until disturbed, and always sits on

the ground amongst dead leaves. Though handsomely coloured on the upper

side, when its wings are closed it closely resembles a dead leaf. It has

a little tail on the lower wing, which looks exactly like the stalk of a

leaf, and from this tail a dark-brown line runs through both wings (which

on the under side are light brown) to the apex of the upper wing. One

would naturally be inclined to look upon this wonderful resemblance to a

dead leaf in a butterfly sitting with closed wings on the ground amongst

real dead leaves as a remarkable instance of protective form and

colouration. And of course it may be that this is the correct

explanation. But what enemy is this butterfly protected against? Upon

hundreds of different occasions I have ridden and walked through forests

where _Precis artexia_ was numerous, and I have caught and preserved many

specimens of these butterflies, but never once did I see a bird

attempting to catch one of them. Indeed, birds of all kinds were scarce

in the forests where these insects were to be found.”

Similarly D. Dewar writes (_Albany Review_, 1907): “If a naturalist be

asked to cite a perfect example of protective colouring, he will, as

likely as not, name the sand grouse (_Pteroclurus exustus_). This species

dwells in open, dry, sandy country, and its dull brownish-buff plumage,

with its soft dark bars, assimilates so closely to the sandy environment

as to make the bird, when at rest, practically invisible, at any rate to

the human eye. Unfortunately for the theory, this bird stands less in

need of protective colouration than any other, for it has wonderful

powers of flight. Even a trained falcon is unable to catch it, because it

can fly upwards in a straight line as though it were ascending an

inclined plane, with the result that the pursuing hawk is never able to

get above it to strike.”

Striped Caterpillars

Lord Avebury, who is a typical Wallaceian, points out the connection that

exists between longitudinal stripes on caterpillars and the habit of

feeding either on grass or low-growing plants among grass. The inference,

of course, is that birds mistake these caterpillars for leaves, or, at

any rate, fail to observe them when feeding, not only because they are

green in colour, but because their longitudinal stripes look like the

parallel veins on the blades of grass. But the butterflies of the family

_Satyridæ_, as Beddard points out, _all_ possess striped larvæ, and these

feed chiefly by night, when neither their colouring nor marking is

visible, while during the day many of them lie up under stones; other

caterpillars of this family feed inside the stems of plants. “Now,”

writes Beddard (_Animal Colouration_, p. 101), “in these cases the colour

obviously does not matter: if, therefore, the longitudinal striping is

kept up by constant selection on account of its utility, and has no other

signification, we might expect that in these two species (_Hipparchia

semele_ and _Œnis_), and in others with similar habits, the cessation of

natural selection would have permitted the high standard required in the

other cases to be lowered—perhaps, even, as has been suggested in the

case of cave animals, the colours being useless to their possessors,

might have disappeared altogether—but they have not.”

Many exceedingly conspicuous birds—as, for example all the crow-tribe,

the egrets, the kingfishers—flourish in spite of their showy plumage.

Such creatures, while scarcely constituting a valid objection to the

theory of protective colouration, serve to show that protective colouring

is not a necessity. An animal otherwise able to take care of itself can

afford to dispense with cryptic colouration. “An ounce of good solid

pugnacity is a more effective weapon in the struggle for existence than

many pounds of protective colouration.”

There used to live in the gardens of the Zoological Society of London a

black cat belonging to the manager of one of the restaurants. This animal

used to catch birds on the lawn. We believe that not even Mr Thayer will

maintain that a black cat is cryptically coloured when stalking on a

well-watered lawn! Nevertheless the nigritude of that cat did not prevent

it securing a meal.

Colours of Eggs

The case of birds’ eggs furnish an excellent example of the lengths to

which Wallace and his followers have pushed the theory of protective

colouration.

D. Dewar maintains that it is possible to divide birds’ eggs that are

coloured, as opposed to those that are white, into two classes—those

which are protectively coloured and those which are not. The former class

includes all those which are laid in shingle or on the bare ground, as,

for example, the eggs of the ring-plover and the lap-wing.[8] He

maintains that the variously coloured and speckled eggs that are laid in

cup-shaped nests are not protectively coloured at all; he declares that

they are usually very conspicuous when in the nest, and, moreover, it

would be futile for them to be cryptically coloured, for a bird or lizard

that habitually sucks eggs will examine carefully the interior of each

nest it discovers.

Needless to say, this view does not appeal to the so-called

Neo-Darwinians. Wallace writes, on page 215 of _Darwinism_: “The

beautiful blue or greenish eggs of the hedge-sparrow, the song-thrush,

the blackbird, and the lesser redpole seem at first sight especially

calculated to attract attention, but it is very doubtful whether they are

really so conspicuous when seen at a little distance among their usual

surroundings. For the nests of these birds are either in evergreen, or

holly, or ivy, or surrounded by the delicate green tints of early spring

vegetation, and may thus harmonise very well with the colours around

them. The great majority of the eggs of our smaller birds are so spotted

or streaked with brown or black on variously tinted grounds that, when

lying in the shadow of the nest and surrounded by the many colours and

tints of bark and moss, of purple buds and tender green or yellow

foliage, with all the complex glittering lights and mottled shades

produced among these by the spring sunshine and sparkling rain-drops,

they must have quite a different aspect from that which they possess when

we observe them torn from their natural surroundings.”

The obvious comment on this is that it is very fine and poetic English,

but it is not science. It is futile to deny what should be obvious to

every field naturalist, namely, that the majority of eggs laid in open

nests are most conspicuous.

D. Dewar thus summarises the main facts which show that eggs in nests (as

opposed to those laid on the bare ground) are not protectively coloured:—

“1. Allied species of birds, even though their nesting habits are very

different, as a rule lay similarly coloured eggs.

“2. Eggs laid in domed nests certainly do not need protective colouring,

yet many of these are coloured.

“3. The same is true of many eggs laid in holes in trees or in buildings.

“4. The protective resemblances of eggs which are laid in the open are

apparent to everyone, which certainly is not true of those deposited in

nests.

“5. Many birds lay eggs which exhibit very great variations.

“6. Some birds lay eggs of different types, and these sometimes differ

from one another so greatly that it is difficult to believe that they

could have been laid by the same species.”[9]

7. It not infrequently happens that one species lays in the disused nest

of another, and the eggs of the latter are often very different in

colouring from those of the former.

We have up to the present considered the theory of general cryptic

colouration, which declares that the majority of creatures are so

coloured as to be inconspicuous. We have still to deal with the

hypothesis of special cryptic colouring.

Certain animals look, when resting, very like an inanimate object, such

as a dead leaf or a twig. This resemblance is said to be the result of

natural selection, since it enables its possessors to escape destruction;

they are seen, but mistaken for something else.

The classical examples of this kind of protective colouring are furnished

by the _Kallimas_ or leaf-butterflies, which display an extraordinary

resemblance to dead leaves.

Other examples are the stick-insects and the lappet moth, which looks

like a bunch of dry leaves. It is needless to multiply instances. In

every work on animal colouration numbers of such cases are cited.

We may grant that in some cases, at any rate, the resemblance is of value

to its possessor, in that it deceives predatory creatures. But it does

not follow from this that the likeness has originated through the action

of natural selection. In order that there can be selection there must be

varying degrees of a tolerable resemblance to select from. How did the

initial similarity arise? This is a matter upon which Wallaceians are

silent. As Poulton truly says, in discussing the degree of protection

afforded by such resemblances, we tacitly endow animals with senses

exactly similar to our own. Are we justified in so doing? Most certainly

not in the case of the invertebrate animals, especially as regards the

arthropods, of which the eyes are constructed very differently from those

of human beings.

D. Dewar has often seen a toad shoot out its tongue and touch a lighted

cigarette end, apparently mistaking it for an insect. Similarly, he has

again and again induced a gecko lizard to chase and try to swallow a

piece of black cotton, one end of which was rolled up into a ball. It is

only necessary to take hold of the unrolled end of the cotton and place

the rolled-up end a few inches from the lizard, and gradually draw it

away in order to induce the lizard to attempt to seize it.

Eyesight of Birds

It would therefore seem that all these elaborate “protective” devices are

unnecessary refinements if regarded as a protection against invertebrate,

reptilian, and amphibian foes. Birds, on the other hand, appear to have

exceedingly sharp eyesight, so that in order to deceive them the

resemblance requires to be very close. Indeed, as regards those birds

which systematically hunt for their prey among leaves and grass, it seems

doubtful whether the alleged “protective” resemblances of caterpillars to

twigs, etc., are sufficient to be of much use to them. Thus Beddard

writes (on page 91 of _Animal Colouration_): “Judging of birds by our own

standard—which is the way in which nearly all the problems relating to

colour have been approached—does it seem likely that we should fail to

see a caterpillar, perhaps as long or longer than the arm, of an

obviously different texture from the branches, and displaying in many

cases through its semi-transparent skin the pulsation of the heart, for

which we were particularly searching?”

Now, birds certainly feed very largely on caterpillars, while they are

but rarely seen to eat butterflies. If, therefore, the aim and object of

these special resemblances is the protection of the species, we should

expect to see them in a nearly perfect state in caterpillars on which

birds feed very largely, and poorly developed in butterflies, which do

not appear to be greatly preyed upon by birds, but have to fear chiefly

the comparatively dull-eyed lizards and mammals, of which the latter hunt

mainly by scent. As a matter of fact, the most striking cases of

resemblance to inanimate objects are seen among butterflies, which seem

to stand least in need of them.

We have already cited the case of the butterfly _Precis artexia_. Even

more marked does the unnecessary elaboration of the likeness seem to be

in the Kallima butterflies.

The Theory of Warning Colouration

All biologists admit that there exist some organisms which are not

coloured so as to be inconspicuous. Indeed, the colouring of certain

species is such as to render them particularly conspicuous. Such species

are said to be warningly coloured. They are supposed to be inedible, or

to have powerful stings or other weapons of defence, or to resemble in

appearance organisms which are thus protected. In the first two cases

they are said to be warningly coloured, and in the last they are cited as

examples of protective mimicry. With the theory of mimicry we shall deal

shortly. We must first discuss the hypothesis of warning colouration.

When animals are unpalatable, or when they possess a sting or

poison-fangs, it is, to use the words of Wallace, “important that they

should not be mistaken for defenceless or eatable species of the same

class or order, since in that case they might suffer injury, or even

death, before their enemies discovered the danger or the uselessness of

the attack. They require some signal or danger-flag which shall serve as

a warning to would-be enemies not to attack them, and they have usually

obtained this in the form of conspicuous or brilliant colouration, very

distinct from the protective tints of the defenceless animals allied to

them” (_Darwinism_, page 232).

Examples of Warning Colouration

For examples of so-called warningly coloured animals, we may refer the

reader to Wallace’s _Darwinism_, Poulton’s _Essays on Evolution_, or

Beddard’s _Animal Colouration_. An instance familiar to all is our

English ladybird. “Ladybirds,” says Wallace, “are another uneatable

group, and their conspicuous and singularly spotted bodies serve to

distinguish them at a glance from all other beetles.”

In order to establish the theory of warning colouration, it is necessary

to prove that all, or the great majority of conspicuously-coloured

organisms, are either unpalatable or mimic unpalatable forms. If this be

so, we are able to understand that the possession of gaudy colouring may

be of advantage to the individual. But even if this be satisfactorily

proved, we must bear in mind that it does not necessarily follow that

these warning colours can be accounted for on the theory of natural

selection. For, in order to explain the existence of any organ by the

action of natural selection, we must be able to demonstrate the utility,

not only of the perfected organ, but of the organ at its very beginning,

and at each subsequent stage of development. This, as we shall show, is

precisely what the Neo-Darwinians are unable to do. We shall have no

difficulty in proving that it would be more advantageous even to a highly

nauseous creature to have remained inconspicuously coloured rather than

to have gradually become more and more conspicuous.

In the first place, let us briefly examine the evidence on which rests

the assertion that all gaudily-coloured insects, etc., are unpalatable,

or possess stings, or mimic forms which are thus armed.

In England wasps, bees, and ladybirds are familiar examples of

conspicuous insects.

The banded black and yellow pattern of the common wasp and the humble bee

are regarded as advertisements or danger signals of the powerful sting.

The red-coat with its black spots is similarly believed to be a warning

that the ladybird is not fit to be eaten.

Caterpillars are usually coloured grey or brown, so as to be

inconspicuous; but numerous exceptions occur which are brightly coloured,

and of these individuals many have been experimentally proved to be

objectionable as food to most insect-eating animals, being either

protected by an unpleasant taste, or covered with hairs or spines.

Familiar cases are those of the abundant and conspicuous black and yellow

mottled caterpillars of the European Buff-tip Moth (_Pygæra bucephala_),

which are much disliked by birds; and the gaily—coloured Vapourer Moth

caterpillar (_Orgyia antiqua_), with its conspicuous tufts of hair.

Readers will remember that a few years back these caterpillars were a

perfect plague in London, in spite of the abundance of sparrows, which

feed freely on smooth green and brown caterpillars.

Oft-cited examples of warning colouration, are the three great groups of

mainly tropical butterflies—the _Heliconidæ_ of America, the _Acræidæ_ of

Africa, and the _Danainæ_ found all over the world. In all of these the

sexes are alike. They are, every one, strikingly coloured, displaying

patterns of black and red, chestnut, yellow, or white. In most

butterflies the lower surface of the wings is of a quiet hue, in order to

render the organism inconspicuous when at rest, but in these warningly

coloured groups the under surface of the wings is as gaudy as the upper

surface. Their flight is slow. They are tough, and exhale a

characteristic odour.

Belt showed that, in Nicaragua, birds, dragonflies, and lizards seem to

avoid the Heliconine butterflies, as the wings of these last are not

found lying about in places where insectivorous creatures feed, whereas

wings of the edible forms are to be found. Moreover, a Capuchin monkey,

kept by Belt, always refused to eat Heliconine butterflies.

Finn investigated the palatability of a number of Indian insects. He

found that most of the birds with which he experimented objected to the

Danaine butterflies; but they disliked still more intensely two

butterflies belonging to groups not universally protected—a swallowtail

(_Papilio aristolochiæ_) and a white (_Delias eucharis_).

Finn further experimented with the tree-shrew or Tupaia (_Tupaia

ellioti_), which feeds largely on insects. He found that this creature

refused most emphatically all these warningly-coloured butterflies. It

would under no circumstances eat the _Danainæ_, whereas the birds would

do so if no more palatable insects were offered to them at the time.

Colonel A. Alcock found that a tame Himalayan bear indignantly refused to

eat a locust (_Aularches militaris_) gaily coloured with black, red, and

yellow, and exhaling an unpleasant-smelling froth; but this bear readily

devoured ordinary brown or green species.

Among cold-blooded vertebrates the common European salamander, with its

bright black and yellow markings, is a striking example of warning

colouration; its skin exudes, on pressure, a very poisonous secretion.

Colonel A. Alcock has described a small siluroid sea-fish, brightly

banded with black and yellow, and armed with poison spines.

A well-known Indian poisonous snake, the banded Krait (_Bungarus

cœruleus_), is conspicuously barred with wide bands of black and yellow;

and in South America there occur numerous species of coral snakes, in

which red is added to these conspicuous colours.

The only known poisonous lizard—the Heloderm of Mexico—is conspicuously

blotched with black and salmon-colour.

Among birds, no instances of warning colouration have been recorded,

though Professor Poulton has suggested that possibly the striking and

contrasted tints of many tropical species may be due to this cause. The

suggestion is an ingenious one, but is at present totally unsupported by

evidence.

The skunks are often cited as an excellent example of warning colouration

among mammals. Skunks are most conspicuously arrayed in black and

white—the latter above, not below, as is usual—and have bushy tails,

which they carry erect. Although less powerful and ferocious than other

members of the weasel family, to which they belong, skunks are

notoriously protected by their abundant secretion of a very fetid liquid.

For further examples of warning colouration we would refer the reader to

Beddard’s illuminating book, entitled _Animal Colouration_.

It should be noticed that in all the cases which we have cited the

colouration is not only conspicuous, but is found in both sexes, whereas

in many undefended animals the male may be just as strikingly coloured,

but the female is not.

We may take it as proved that there is a very general relation between

gaudy colouring and inedibility, or rather unpalatability, among insects.

It may safely be said that any species of insect which lives, either as

an adult or as a larva, in the open will perish in the struggle for

existence if, being conspicuously coloured, it is neither inedible nor

armed with a weapon such as sting, nor provided with a thick cuticle, nor

resembles in appearance some creature which is protected.

Warning Colouring a Drawback

But from this it is not legitimate to conclude, as Neo-Darwinians do,

that these brilliant colours have been slowly brought into being by

natural selection.

Why should any creature, having by the “luck” of variation and heredity

acquired some quality—be it strength, pugnacity, sting, or unpleasant

taste—which renders it comparatively immune from persecution, proceed to

advertise the fact by assuming a gaudy or striking colour? It would

surely be better for such an organism to remain inconspicuous. By

becoming showy it is visible to every young bird who, not having yet

learned that the creature in question is unfit for food, seizes and

perhaps kills it. It is true that the young bird vows that never again

will it touch another such organism. But of what avail to the dying

example of warning colouration is the resolution of the young bird?

Moreover, the organism in question, by being conspicuous, also advertises

itself to those few enemies which will eat it. There are always, as

Professor Poulton justly remarks, animals which are enterprising enough

to take advantage of prey which has at least the advantage of being

easily seen and caught.

Conspicuous Animals Attacked

It is possible to cite cases where animals, notwithstanding the fact that

they possess natural defences, become the prey of others in some

exceptional cases.

The salamander can be eaten with comparative impunity by the toad, a

creature very likely to meet with it.

The toad itself may be eaten; Finn saw the Indian toad (_Bufo

melanostictus_) eat another of its own kind. He further observed that the

Indian water-snake (_Tropidonotus piscator_) and the “Crow pheasant”

cuckoo (_Centropus sinensis_), in the free state, and the Indian Roller

(_Coracias indica_) and the Pied Hornbill (_Anthracoceros_), in

captivity, eat the warningly-coloured toad. On the other hand, a captive

Racket-tailed drongo rejected toads when offered to it. The common cuckoo

is well known to feed on hairy and “warningly-coloured” caterpillars.

Finn has also seen the glossy cuckoo in Zanzibar devouring

black-and-yellow caterpillars. Moreover, in America crows are found to

select deliberately highly polished and strongly flavoured beetles. Yet

again, wasps are preyed upon by bee-eaters, and also eaten by our common

toad. In India, Finn found, by many experiments, that the common garden

lizard, or “bloodsucker” (_Calotes versicolor_), would eat, both in

captivity and in freedom, all “warningly-coloured” butterflies, not only

the _Danainæ_, but even _Delias eucharis_ and the pre-eminently nauseous

_Papilio aristolochiæ_. That this reptile is a great enemy to butterflies

is rendered probable by the frequent occurrence of specimens of these

insects with its semicircular bites in their wings.

Further, Finn found that bulbuls, the commonest garden birds in India,

ate the _Danainæ_ readily in captivity, even when other butterflies could

be had, which was not the case with most other birds. Bulbuls did,

however, usually refuse the _Delias_ and _Papilio_ mentioned above.

The Skunk is preyed upon in America by the Eagle-owl (_Bubo virginianus_)

and the Puma.

Thus, animals provided with natural defences are not immune from attack.

Hence natural selection cannot have encouraged the survival of

individuals which displayed a conspicuous colour, for the sake of the

“warning.”

We must not forget that many creatures armed with powerful weapons

possess the unobtrusive drab, brown, or green colouration which is

associated with concealment from foes.

There can be little doubt that, but for the fact that the hive-bee can

inflict a sting more severe than that of the wasp, this useful insect

would have been cited as a case of a protectively coloured creature.

Notwithstanding its sober brown colouring, the hive-bee is recognised and

avoided.

Professor Poulton records that the dull inconspicuous caterpillar of the

moth (_Mænia typica_) is rejected by reptiles. It must be admitted,

however, that these cases among insects are very rare.

The smooth newt (_Molge vulgaris_), a relation of the salamander, is

protected by a poisonous skin; nevertheless the creature has a dark brown

back and spends most of its time on land. Its black-spotted, yellow

under-surface may have some protective value in the water. Neither the

pike nor the common European water-tortoise will eat this newt.

Toads are nearly all very inconspicuous; nevertheless they are well

protected by the acrid secretion from the skin glands; moreover, they are

both recognised and avoided by those predacious creatures to whom they

are distasteful. Hawks, although as a rule plainly coloured, are

certainly recognised by all other birds. It would seem, therefore, that

“warning colours,” like the similar striking hues of many domestic

animals, are incidental attributes. It has been possible for their owners

to develop them, because for the most part let alone.

Eisig, long ago, pointed out that the brightly coloured pigment in the

skin of these warningly coloured insects is in certain cases of an

excretory nature. Therefore the inference which should be drawn is, as

Beddard points out on page 173 of his _Animal Colouration, “that the

brilliant colours_ (i.e. _the abundant secretion of pigment_) _have

caused the inedibility of the species, rather than that the inedibility

has necessitated the production of bright colours as an advertisement_.”

In other words, Neo-Darwinians put the cart before the horse!

[Illustration: BOURU FRIAR-BIRD]

[Illustration: BOURU ORIOLE]

In some cases these brilliantly coloured insects may be survivals of an

age in which there were no birds. When these came into being and began to

prey upon insects, the conspicuously coloured species which were not

inedible or very unpalatable would soon become extinct, while those that

were inedible would survive as warningly-coloured insects. In other cases

it is not improbable that these warningly-coloured creatures have arisen

by mutations from more soberly-hued insects. It is conceivable that every

now and again a mutation occurs which renders its possessor conspicuous.

This will result in the early destruction of these aberrant individuals

unless their newly-acquired gaudiness is either correlated with, or the

result of, distastefulness.

Aposematic Sounds

In the case of warning colouration, the Neo-Darwinians have, as usual,

pursued their theory to absurd lengths. Professor Poulton, for example,

extends it to sounds and attitudes. “Sound,” he writes, on page 324 of

_Essays on Evolution_, “may be employed as an Aposematic character, as in

the hiss of some snakes and some lizards. Certain poisonous snakes when

disturbed produce by an entirely different method a far-reaching sound

not unlike the hiss. Thus the rattle-snake (_Crotalus_) of America

rapidly vibrates the series of dry, horny, cuticular cells, movably

articulated to each other and to the end of the tail. The stage through

which the character probably arose is witnessed in another genus which

vibrates its tail among dry leaves, and thus produces a warning sound.

The deadly little Indian snake (_Echis carinata_) (‘the Kuppa’) makes a

penetrating swishing sound by writhing the coils of its body one over the

other. Special rows of the lateral scales are provided with serrated

keels which cause the sound when they are rubbed against each other.

Large birds, when attacked, often adopt a threatening attitude,

accompanied by an intimidating sound which usually suggests more or less

closely the hiss of a serpent, and thus includes an element of mimicry. .

. . The cobra warns an intruder chiefly by attitude and by the broadening

of its flattened neck, the effect being heightened in some species by the

‘spectacles.’ In such cases we often witness a combination of cryptic and

Aposematic methods, the animal being concealed until disturbed, when it

instantly assumes a warning attitude.

“The benefit of such intimidating attitudes is clear: a venomous snake

gains far more advantage by terrifying than by killing an animal it

cannot eat. By striking, the serpent temporarily loses its poison, and

with this a reserve of defence. Furthermore, the poison does not cause

immediate death, and the enemy would have time to injure or destroy the

snake.”

Intimidating Attitudes

At first sight this reasoning may seem very convincing. But consider for

a moment the process by which the hiss originated and gradually increased

by natural selection. We must suppose that the rattle-snake was formerly

incapable of making any sound. One day a variety appeared in which the

skin was slightly hardened, so that when the creature moved its body

rapidly there issued a slight sound. This must have caused an enemy to

refrain from attack; it thus lived to transmit this peculiarity to its

offspring, and those which made more noise than their ancestors escaped,

while those that made less succumbed to their enemies. For ourselves, we

find it quite impossible to believe that the rattle was thus gradually

evolved by means of natural selection. Indeed, we are inclined to think

that neither the hiss of the cobra nor its “intimidating attitude” has

any terrifying effect on its adversary. In the case of the cobra we are

able to cite positive evidence that dogs and cattle show no alarm at the

attitude.

“Dogs,” writes D. Dewar of this display, “regard it as a huge joke. Of

this I have satisfied myself again and again, for when out coursing at

Muttra we frequently came across cobras, which the dogs used invariably

to chase, and we sometimes had great difficulty in keeping the dogs off,

since they seemed to be unaware that the creature was venomous.”

Colonel Cunningham writes, on page 347 of _Some Indian Friends and

Acquaintances_: “Sporting dogs are very apt to come to grief where cobras

abound, as there is something very alluring to them in the sight of a

large snake when it sits up nodding and snarling; and it is often

difficult to come up in time to prevent the occurrence of irreparable

mischief.”

Colonel Cunningham also states that many ruminants have a great animosity

to snakes, and are prone to attack any that they may come across.

We may therefore well be sceptical as to the value of intimidating

attitudes to those creatures which are in the habit of striking them.

Mimicry

In a work of this kind it is neither possible nor necessary to consider

in great detail the mass of evidence which has been advanced in favour of

the theory of mimetic resemblance.

Chapters vii. and viii. of Professor Poulton’s _Essays on Evolution_

contain an up-to-date statement of the facts in favour of the theory.

Professor Poulton believes that in all cases mimetic resemblance is the

result of the action of natural selection.

He admits that there is no direct evidence in its favour, but asserts

that “the facts of the cosmos, so far as we know them, are consistent

with the theory, and none of them inconsistent with it” (page 271).

Theory of Protective Mimicry

We are not at all sure that no facts are against the theory of protective

mimicry. We shall presently set forth some which to us seem, if not

actually inconsistent with the theory, at least to point to the

conclusion that the phenomenon may be explained otherwise than as a

product of natural selection.

Evidence for the Theory

Let us first briefly state the case for the theory of protective mimicry.

1. It is asserted that the mimicking species and that which is mimicked

are often not nearly related. For example, the unpalatable larva of the

Cinnabar Moth (_Euchelia jacobaeæ_) is said to mimic a wasp, because it

has black and yellow rings round its body.

“The conclusion which emerges most clearly,” writes Poulton (p. 232), “is

the entire independence of zoological affinity exhibited by these

resemblances.” This is supposed to be proof that Darwin was wrong when he

asserted that the original likeness was due to affinity. Says Poulton:

“The preservation of an original likeness due to affinity undoubtedly

explains certain cases of mimicry, but we cannot appeal to this principle

in the most remarkable instances.”

2. It is asserted that species which are mimicked are invariably either

armed with a sting, well defended, or unpalatable, so that it is against

the interest of insectivorous creatures to attack them. It is further

asserted that the species imitated are “even more unpalatable than the

generality of their order.”

3. It is pointed out that the most distasteful groups of butterflies—the

_Danaidæ_, the _Acræinæ_, the _Ithomiinæ_, and the _Heliconinæ_—consist

of large numbers of species which closely resemble one another. This is

said to be due to Müllerian mimicry. Mayer states that in South America

there are 450 species of inedible _Ithomiinæ_ which display only 15

distinct colours, while the 200 species of _Papilio_, which are edible,

exhibit 36 distinct colours. Nevertheless, he says, there is no lack of

individual variability among the former hence their conservatism as

regards colour cannot be attributed to their having but little tendency

to vary.

4. It is asserted that although in many cases the mimetic resemblances

extend to the minutest detail, nevertheless they are not accompanied by

any changes in the mimetic species except such as assist in the

production or strengthening of a superficial likeness.

Pictures illustrating such cases of mimicry are figured on pp. 241, 247,

and 251 of Wallace’s _Darwinism_ (1890 edition).

5. It is stated that mimetic resemblance is not confined to colour, but

extends to pattern, form, attitude, and movement; that deep-seated organs

are affected when the superficial resemblance is intensified, but not

otherwise. Poulton cites _Clytus arietis_, the “wasp-beetle,” as an

example of this.

6. It is asserted that mimetic resemblances are produced in the most

diverse ways; that the modes whereby the similarity in appearance is

brought about are varied, but the result is uniform.

“A lepidopterous insect,” writes Poulton (p. 251), “requires above all to

gain transparent wings, and this, in the most striking cases that have

been studied, is produced by the loose attachment of the scales, so that

they easily and rapidly fall off and leave the wing bare except for a

marginal line and along the veins (_Hemaris_, _Trochilium_).”

7. It is alleged that the imitator and imitated are always found in the

same locality. If they did not do so no advantage would be derived from

the resemblance. It is further alleged that where the mimicking species

is edible it is invariably less abundant where it occurs than the species

it imitates.

8. It is pointed out that it sometimes happens that where in the mimic

the sexes differ in appearance, the male copies one species, the female

quite a different one. This is said to be because the deception would be

liable to be detected if the mimicking species became common relatively

to that which is imitated. “We therefore find that two or more models are

mimicked by the same species” (_Essays on Evolution_, p. 372).

Occasionally the female mimics two other species, _i.e._ she occurs in

two forms, each like a different species.

It sometimes happens that the female alone mimics. This is said by

Wallace to be due to her greater need of protection. When she is laden

with eggs her flight is slow, and therefore she requires a special degree

of protection.

9. It is said that in some species we find a non-mimetic ancestor

preserved on islands where the struggle for existence is less severe,

while on the adjacent continent mimicry has been developed.

10. It is alleged that in the cases where moths resemble butterflies the

former are either as diurnal as the butterflies or are species which

“readily fly by day when disturbed.”

11. It is asserted that some seasonally dimorphic forms are examples of

mimicry only in one state, in the form that comes into being at the time

when the struggle for existence is most severe; that is to say, in the

dry season, in Africa, when insect life is far less abundant than in the

rainy season.

In other cases the mimicry of the dry-weather form is said to be far more

perfect.

Instances of this phenomenon are set forth in Professor Poulton’s _Essays

on Evolution_.

Alternative Theories

It will be observed that we have quoted very largely from Professor

Poulton’s work. Our reason for so doing is that he appears to be the most

prominent advocate of the theory of protective mimicry, and his work,

which was published in 1908, may be taken as the latest Neo-Darwinian

pronouncement on the subject.

Hence if we can show, as we believe we can, that his arguments are not

sound, we may take it that we have demonstrated that the theory in its

present form is untenable.

It is worthy of notice that Professor Poulton sets forth three other

suggestions which have been proposed as substitutes for natural selection

as an explanation of the phenomena of mimicry.

The first is the theory of External Causes, namely, that the resemblance

is due to some external cause, such as food or climate.

The second is the theory of Internal Causes, which states that mimetic

resemblance is due to internal developmental causes.

The third is the suggestion that sexual selection has caused the origin

of these resemblances.

He then proceeds to demolish these to his own satisfaction, and adds

triumphantly, “The conclusion appears inevitable that under no theory,

except natural selection, do the various resemblances of animals to their

organic and inorganic environments fall together into a natural

arrangement and receive a common explanation” (p. 228).

To reasoning of this description there is an obvious reply. Even if it be

granted that the alternatives to the theory of natural selection as set

forth by Professor Poulton are untenable, it does not follow that natural

selection affords an adequate explanation. If A, B, C and D are charged

with theft and the prosecutor proves that neither A nor B nor C committed

the theft, this will not suffice to secure the conviction of D. It is

quite possible that a fifth person, E, may be the culprit.

Much of the popularity of the theory of natural selection is due to the

fact that biologists have not yet been able to discover a substitute for

it.

It seems to us that the proper method of making progress in science is

not to bolster up natural selection by ingenious speculations, but to

look around for other hitherto undiscovered causes.

[Illustration: KING-CROW OR DRONGO]

[Illustration: DRONGO-CUCKOO]

Objections to the Theory that the so-called Cases of Mimicry owe their

Origin to Natural Selection

It is obvious that for one creature to resemble another can be of little

or no benefit to either until the resemblance is tolerably close. It is,

therefore, insufficient to prove the utility of the perfected

resemblance. We may readily grant this and yet maintain that the origin

of the resemblance cannot be due to the action of natural selection.

The Drongo-cuckoo (_Surniculus lugubris_) displays so great a likeness to

the King Crow (_Dicrurus ater_) that it is frequently held up by

Neo-Darwinians as an excellent example of mimicry among birds. But D.

Dewar writes, on page 204 of _Birds of the Plains_: “I do not pretend to

know the colour of the last common ancestor of all the cuckoos, but I do

not believe that the colour was black. What then caused _Surniculus

lugubris_ to become black and assume a king-crow-like tail?