“A black feather or two, even if coupled with some lengthening of the

tail, would in no way assist the cuckoo in placing its egg in the

drongo’s nest. Suppose an ass were to borrow the caudal appendage of the

king of the forest, pin it on behind him, and then advance among his

fellows with loud brays, would any donkey of average intelligence be

misled by the feeble attempt at disguise? I think not. Much less would a

king-crow be deceived by a few black feathers in the plumage of a cuckoo.

I do not believe that natural selection has any direct connection with

the nigritude of the drongo-cuckoo.”

Darwin was fully alive to this difficulty when he wrote: “As some writers

have felt much difficulty in understanding how the first step in the

process of mimicry could have been effected through natural selection, it

may be well to remark that the process probably commenced long ago

between forms not widely dissimilar in colour” (_Descent of Man_, 10th

Ed., p. 324). Such a statement is of course quite inconsistent with the

Neo-Darwinian position. “The conclusion which emerges most clearly,”

writes Poulton (_Essays on Evolution_, p. 232), “is the entire

independence of zoological affinity exhibited by these resemblances; and

one of the rare cases in which Darwin’s insight into a biological problem

did not lead him right was when he suggested that a former closer

relationship may help us to a general understanding of the origin of

mimicry. 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.”

It is unnecessary to labour this point. It is surely evident to everyone

with average intelligence that, until the resemblance between two forms

has advanced a considerable way, the likeness cannot be of utility to

either, or at any rate of sufficient utility to give its possessor a

survival advantage in the struggle for existence. Until it reaches this

stage, natural selection cannot operate on it. It is therefore absurd to

look upon natural selection as the direct cause of the origin of the

likeness. When once a certain degree of resemblance has risen, it is

quite likely that in some cases natural selection has strengthened the

likeness.

The second great objection to the Neo-Darwinian explanation of the

phenomenon known as mimicry is that in many cases the resemblance is

unnecessarily exact. Even as we saw how the Kallimas, or dead-leaf

butterflies, carried their resemblance to dead leaves to such an extent

as to make it appear probable that factors other than natural selection

have had a share in its production, so do we see in certain cases of

mimetic resemblance an unnecessarily faithful likeness.

The Brain-fever Bird

The common Hawk Cuckoo of India (_Hierococcyx varius_) furnishes an

example of this: “The brain-fever bird,” writes Finn, on page 58 of

_Ornithological and Other Oddities_, “is the most wonderful feather copy

of the Indian Sparrow-hawk or Shikra (_Astur badius_). All the markings

in the hawk are reproduced in the cuckoo, which is also of about the same

size, and of similar proportions in the matter of tail and wing; and both

hawk and cuckoo having a first plumage quite different from the one they

assume when adult, the resemblance extends to that too. Moreover, their

flight is so much the same that unless one is near enough to see the

beak, or can watch the bird settle and note the difference between the

horizontal pose of the cuckoo and the erect bearing of the hawk, it is

impossible to tell them apart on a casual view.” Moreover, the tail of

the cuckoo sometimes hangs down vertically, thus intensifying the

likeness to the hawk.

It is quite possible that the brain-fever bird derives some benefit from

the resemblance; indeed, it has been seen to alarm small birds, even as

the hawk-like common cuckoo frightens its dupes, but, as D. Dewar pointed

out, on page 105 of vol. 57 of the _Journal of the Society of Arts_,

“this is not sufficient to explain a likeness which is so faithful as to

extend to the marking of each individual feather. When a babbler espies a

hawk-like bird, it does not wait to inspect each feather before fleeing

in terror; hence all that is necessary to the cuckoo is that it should

bear a general resemblance to the shikra. The fact that the likeness

extends to minute details in feather marking, points to the fact that in

each case identical causes have operated to produce this type of

plumage.” This conclusion is still further strengthened by the fact that

the likeness extends to the immature plumage, that is to say, exists at a

time when it cannot assist the cuckoo in its parasitical work.

Poulton meets this objection as follows:

[Illustration: SHIKRA HAWK]

[Illustration: HAWK-CUCKOO]

Hypertely

“All such criticism is founded on our imperfect knowledge of the struggle

for existence. The impressions and judgments of man are immensely

influenced by the ‘corroborative detail,’ giving ‘artistic verisimilitude

to a bold and unconvincing narrative.’ Indeed, the laughter which is

invariably raised by this passage from _The Mikado_ is, I have always

thought, not only or chiefly due to the humour of the application, but to

the way in which a great and familiar truth breaks in upon the listener

with all the pleasing surprise which belongs to epigram. Birds, the chief

enemies of insects, are known to have powers of sight far superior to

those of man, and, from our experience of them in captivity, it may be

safely asserted that their attention is attracted by excessively minute

detail. Until our knowledge of the struggle for life is far more

extensive than at present, the argument founded on Hypertely may be left

to contend with another argument often employed against the explanation

of cryptic and mimetic resemblance by natural selection. Hypertely

assumes that there are unnecessary details in the resemblance, that the

resemblance is perfect beyond the requirements of the insect; the second

argument maintains that birds are so supremely sharp-sighted that no

resemblance, however perfect, is of any avail against them. In the

meantime the majority of naturalists will probably reject both extremes,

and believe that the enemies are certainly sharp-sighted and successful

in pursuit, but that perfection in detail makes their task a harder one,

and gives to the individuals possessing it in a higher degree than

others, increased chances of escape, and of becoming the parents of

future generations.” (_Essays on Evolution_, p. 302.)

This long quotation requires careful consideration, since to us it

appears to be typical of the kind of reasoning resorted to by

Neo-Darwinians.

Note the reference to our “imperfect knowledge of the struggle for

existence.” This is almost invariably the last refuge of the

Neo-Darwinian when worsted in argument. We fully admit that there is

still much to be learned of the nature of the struggle for existence, but

such a statement sounds very curious when uttered to those who pin their

faith to the theory which sees in the principle of natural selection an

explanation of all the phenomena of the organic world. Natural selection,

be it remembered, is but a name for the struggle for existence.

Birds capturing Butterflies

“Birds,” says Professor Poulton, “are the chief enemies of insects.” This

may be so. But we greatly doubt whether they are the chief enemies of

butterflies and moths, among which the most perfect examples of mimicry

are supposed to occur.

We have watched birds closely for some years, but believe that we could

almost count on our fingers the cases in which we have seen a bird chase

a butterfly.

Professor Poulton, being aware of this objection, sets forth, on pp.

283-292 of _Essays on Evolution_, the evidence he has gathered in favour

of the view that birds are the chief enemies of butterflies and other

lepidoptera.

As the result of five years’ observation in S. Africa, Mr G. A. K.

Marshall was able to record some eight cases of birds capturing

butterflies. In three cases the butterfly seized was warningly coloured,

or, at any rate, conspicuous! In two of these eight cases the bird failed

to capture its quarry!

Says Mr Marshall, “the fact that birds refrain from pursuing butterflies

may be due rather to the difficulty in catching them than to any

widespread distastefulness on the part of these insects.”

During six years’ observation in India and Ceylon, Colonel Yerbury

records some half dozen cases of birds capturing, or attempting to

capture, insects. He writes: “In my opinion an all-sufficient reason for

the rarity of the occurrence exists in the fact that in butterflies the

edible matter is a minimum, while the inedible wings, etc., are a

maximum.”

Colonel C. T. Bingham in Burma states that between 1878 and 1891 he on

two occasions witnessed the systematic hawking of butterflies by birds,

although he observed on other occasions some isolated cases.

This appears to be the sum total of the evidence adduced by Professor

Poulton as regards the capture of butterflies by birds. This seems to us

an altogether insufficient foundation upon which to build the theory that

the cases of resemblance between unrelated species have been effected by

natural selection.

It is, however, to be noted that probably among birds the most dangerous

enemies of butterflies are not those that habitually catch insect prey on

the wing. Such are experts in the art of fly-catching, and would despise

the comparatively meatless butterfly. One often comes across butterflies

with an identical notch in each wing, which leaves little room for doubt

that those particular butterflies had been snapped at, _while resting_,

by a bird. Among birds the chief enemies of butterflies and moths are

probably to be found in those that hunt for their food in bushes and

trees.

Thus, what we do know of the nature of the struggle for existence offers

but poor support to the Neo-Darwinian explanations of the cases of

so-called mimicry in nature.

Observing-powers of Birds

Professor Poulton’s idea of pitting the argument of Hypertely against

that of the alleged supreme sharp-sightedness of birds is ingenious, but

is not likely to satisfy very many people save those content to live in a

fools’ paradise. If birds are supremely sharp-sighted, and pay attention

to excessively minute detail, the difficulty of accounting for the

_origin_ of protective mimicry on the natural selection hypothesis

becomes all the greater.

The question whether or not birds are good observers is a most

interesting one. Unfortunately, hitherto, but little attention has been

paid to the subject. The evidence available seems to point to the fact

that birds, like savages, have sharp eyes only for certain objects—that

is to say, for the things they are accustomed to look out for. All

observers of nature must have noticed how quick a butcher-bird is to

catch sight of a tiny insect upon the ground at a distance of some yards

from his perch.

On the other hand, it is said that when there is snow upon the ground

wood pigeons will approach quite close to a man wearing white clothes and

a white hat, provided he keep perfectly still. Finn once witnessed in

Calcutta a sparrow pick up a very young toad, obviously by mistake, for

it dropped it at once with evident distaste. Birds of prey are supposed

to have remarkably good eyesight; yet they can readily be caught by a net

stretched out before their quarry. They are not trained to be on the

watch for such things as nets, and so do not appear to notice one when

erected.

It is thus our belief that the very perfection and detail of some

so-called mimetic resemblances are a very serious objection to the theory

of protective mimicry as enunciated by Professor Poulton and other

Neo-Darwinians.

There is yet a further objection to this theory, one which, in our

opinion, is fatal to the hypothesis in its generally accepted form.

A number of cases occur where two species, in no way related, show close

resemblance to one another under such circumstances that neither can

possibly derive any benefit from the likeness. The theory of protective

mimicry is quite unable to explain these cases. This fact leads to a

suspicion that, in the instances where the theory does at first sight

appear to offer an explanation, the resemblance may also be due to mere

coincidence.

We may perhaps call the cases which the theory of mimicry is unable to

account for “false mimicry,” but in so doing we must bear in mind the

possibility that some, at any rate, of the examples of so-called mimicry

may, on further investigation, prove to be nothing of the kind.

“False” Mimicry among Mammals

The Cacomistle of Mexico (_Bassaris astuta_), one of the raccoon family,

has a grey body and long black-and-white ringed tail, just like the

ring-tailed Lemur of Madagascar (_Lemur catta_); both are arboreal and

about the same size, and this lemur’s colouration is exceptional in its

family.

The banded Duiker-buck of West Africa (_Cephalophus doriae_), has the

same very unusual colouration as the thylacine or marsupial wolf of

Tasmania, light brown, with bold black bands across the hinder part of

the back, and the animals are about the same size.

The dormouse of Europe closely resembles a small American Opossum

(_Didelphys murina_), and a larger opossum (_D. crassicaudata_) is very

like the Siberian Mink (_Mustela sibirica_).

The Flying Squirrel of North America (_Sciuropterus volucella_) is

closely copied by the Flying Phalanger (_Petaurus breviceps_) of

Australia.

It will be readily seen that in no one of these cases can the likeness be

of utility to either the “model” or the “copy.”

False Batesian Mimicry among Birds

There are many instances of this phenomenon among birds. The New Zealand

Cuckoo (_Urodynamis tritensis_) shows a far closer resemblance to the

American Sparrow-hawk (_Accipiter cooperi_) than to any New Zealand hawk,

and in fact closely mimics this quite alien bird.

The stormy petrel, a purely oceanic bird, closely resembles in size,

colour, and style of flight the Indian Swift (_Cypselus affinis_), a

purely inland creature; both are sooty black, with a conspicuous white

patch on the lower back.

The Pied Babbling Thrush (_Crateropus bicolor_) of Africa is singularly

like the Pied Myna (_Græulipica melanoptera_) of Java, both being of

about the same size, with white body and black wings and tail quills.

This, we may add, is a very unusual colouration among small birds.

The black-headed Oriole (_Oriolus melanocephalus_) of India is very

similar in appearance to the common Troupial (_Icterus vulgaris_) of

Brazil; indeed, the troupials, a purely American group, are so like the

old world orioles in colour that they usurp their name in America.

The little insectivorous Iora (_Ægithina tiphia_) of India strongly

resembles in size and colour a Siskin (_Chrysomitris colambiana_) from

South America, the males in both being black above and yellow below,

while in the females the black is replaced by olive-green.

Another Indian babbler (_Cephalopyrus flammiceps_), yellowish-green, with

orange forehead, is closely copied by, or copies, the well-known

Brazilian Saffron-finch (_Sycalis flaveola_).

In Fergusson Island, near New Guinea, there is a ground pigeon

(_Otidiphaps insularis_) which is black with chestnut wings, like several

of the powerful ground cuckoos of the genus _Centropus_, but no species

of these cuckoos so coloured appears to inhabit the island.

In Africa there is a tit (_Parus leucopterus_) which has the same very

unusual colouration as an East-Indian bulbul (_Micropus melanoleucus_),

both being black with a white patch on the wing-coverts. These two birds

are about the same size. As showing the purely coincidental character of

such resemblances, we may mention that this same rare pattern occurs

again in our Black Guillemot (_Uria grylle_) and in the Muscovy Duck

(_Cairina moschata_).

We have already quoted Gadow (p. 198) on “false mimicry” among snakes. He

also gives, on p. 110 of _Through Southern Mexico_, an example of this

phenomenon among amphibia. It is, he writes, “impossible to distinguish

certain green tree-frogs of the African genus _Rappia_ from a _Hyla_,

unless we cut them open. If they lived side by side, which they do not,

this close resemblance would be extolled as an example of mimicry.”

We should be very greatly surprised if abundant examples of “false

mimicry” are not found among insects. We trust that this remark will

stimulate some entomologist to pay attention to the subject.

It is the essence of Müllerian mimicry that both model and copy are

immune from attack from enemies. Unfortunately for the theory, similar

resemblances occur among birds of prey, where neither party can benefit

from the association. This gives rise to what we may perhaps call false

Müllerian mimicry. Thus the goshawk and peregrine falcon resemble each

other in being brown above and streaked below in immature plumage, and

having barred underparts and a grey upper plumage when adult.

Theory of Mimicry Criticised

Having stated the more important objections to the theory of protective

mimicry, it now remains for us to deal specifically with each head of

evidence offered in its favour.

1. With regard to the assertion that the model and its copy are often not

nearly related, we have shown that among mammals and birds instances of

resemblance between widely-separated groups occur under such

circumstances that neither party can derive any benefit therefrom.

2. As regards the assertion that species which are mimicked are either

well-defended or unpalatable, this certainly does not hold good with

regard to some at any rate of the coincidental resemblances among birds

which we have pointed out; even if these pairs of similar species lived

in the same country it would require considerable ingenuity to say why

one should mimic the other.

3. As regards the argument that the inedible species of _Ithomiinæ_,

etc., display only fifteen colours, while the less numerous edible

_Papilios_ display more than double this number of colours, we may draw

attention to the fact that those birds which are most immune from attack

are precisely those which display the smallest range as regards colour,

e.g., hawks, owls, crows, gulls, storks, and cranes. As we have already

submitted, no question of Müllerian association comes in here.

On the other hand, the eminently edible families of game-birds and ducks

display great variety of colour, in the males at all events.

4. As regards the statement that although in many cases the mimetic

resemblances extend to the minutest detail, they are not accompanied by

any structural changes except such as assist in the production of a

superficial likeness, we may refer to the case we have already cited of

the New Zealand cuckoo, which, though it so closely copies an American

hawk, is typically cuculine in structure. Here, of course, there can be

no question of advantage to the “mimicking” cuckoo in the resemblances.

5. In answer to the argument that mimetic resemblance extends to form,

attitude, and movement, as well as colour, and that deep-seated organs

are affected only when the superficial resemblance is thereby

intensified, we may draw attention to such cases as the following:—

(_a_) The harmless Indian Snake (_Lycodon aulicus_) is closely similar to

the well-known Krait (_Bungarus cœruleus_), also Indian; but the

resemblance extends to a structural detail which can hardly have mimetic

value—namely, the harmless snake has long, fang-like front teeth, though

these are unconnected with poison-glands. Animals which come into contact

with the krait and its mimic are hardly likely to inspect their teeth.

(_b_) A considerable number of birds of the shrike group—known as

Cuckoo-Shrikes (_Campophaga_)—closely resemble cuckoos in plumage; but

even if they derive any benefit from mimicking birds which are credited

with being mimics already, they cannot profit by the fact that the shafts

of the rump-feathers in both groups are stiffened; this being a

peculiarity which would not be perceptible until the bird was in the

grasp of an aggressor.

(_c_) As a third case of coincidence we may refer to the tubercle in the

nostril of the Brain-fever-bird (_Hierococcyx varius_), as a minute

detail of hawk-like appearance, though not present in the particular

species imitated.

6. The argument that mimetic resemblances are produced in the most

diverse ways, but the result is uniform, loses much of its force when we

consider the various methods by which short-tailed birds appear to have

long caudal appendages.

In the peacock it is the upper tail coverts which are elongated; in the

Stanley Crane (_Tetrapteryx paradisea_) it is the innermost or tertiary

quills of wing; in one of the egrets some of the feathers of the upper

back grow to a great length and form a train; in the Bird of Paradise

(_Paradisea apoda_) the long flank plumes are commonly mistaken for the

tail.

In these cases there can be no question of mimicry.

7. We have shown that the idea that imitator and imitated are always

found in the same area is absolutely fallacious. In birds, for example,

the most striking resemblances appear to occur between species that dwell

far apart.

8. We can cite, as parallel to the case of a mimicking species of which

the male copies one model and the female another, the strange similarity

between the barred brown plumage of the female blackcock and that of the

female eider-duck. The males of these species, although both black and

white, differ greatly in appearance; but the male blackcock is admittedly

very like the male of another species of sea-duck—the scoter.

9. Against the supposed ancestral non-mimetic forms existing on islands

we can pit the “mimetic” orioles in small islands and their non-mimetic

cousins on the mainland. In Australia an oriole of what appears to be an

ancestral style lives beside, but declines to mimic, a friar bird of a

very pronounced type.

10. The case of certain diurnal moths mimicking butterflies appears to be

explicable without the aid of the theory of protective mimicry. When two

species adopt the same method of obtaining food, it not infrequently

happens that a professional likeness springs up between them. Of this the

swifts and swallows afford a striking illustration.

11. As a set-off to the cases where the alleged mimicry is confined to

certain seasons of the year, we may cite the case of the pheasant-tailed

Jaçana (_Hydrophasianus chirurgus_), which in its winter plumage might

easily be mistaken, when on the wing, for the paddy bird or Pond Heron

(_Ardeola grayii_), both being of like size and having a brown back, long

green legs, and white wings. Moreover, they are to be found in the same

localities in India. At the breeding season, however, they are absolutely

different in plumage.

Yet another argument commonly adduced in favour of the theory of

protective mimicry is that local variations of the imitated species are

sometimes followed by the imitator; thus the butterfly _Danais

chrysippus_ shows a white patch on the hind wings in Africa, and this is

followed by its mimic.

But the same thing occurs, quite irrationally, so to speak, among birds.

The peregrine falcon and hobby of Europe are only winter migrants to

India, where they are replaced as residents by the Shaheen (_Falco

peregrinator_) and Indian Hobby (_F. severus_). Both these differ from

the migratory forms by being blacker above and chestnut below, instead of

cream colour. Thus the resemblance occurs in each race. A similar

distinction, as noted by Blyth, exists between the Common Swallow

(_Hirundo rustica_) and the Swallow (_H. tytleri_) of Eastern Asia, the

latter having the whole ventral surface rufous instead of only the

throat. Yet no one will suggest that swallows mimic falcons, or that

there is mimicry between the peregrine and hobby. It is obvious that such

parallel changes occur independently of mimicry.

The Water-rail (_Rallus aquaticus_) and Baillon’s Crake (_Porzana

bailloni_) of Europe are distinguished from their allies of Eastern Asia

by having the sides of the head plain grey, whereas the Eastern Asiatic

forms (_R. indicus_ and _P. pusilla_) have a brown streak along each side

of the face. Here, again, we have an instance of birds of the same family

varying together with geographical distribution.

“Recognition” Colours

One of the prettiest conceits of the Wallaceian school of zoologists is

the theory of recognition markings.

“If,” writes Wallace, on page 217 of _Darwinism_, “we consider the habits

and life-histories of those animals which are more or less gregarious,

comprising a large proportion of the herbivora, some carnivora, and a

considerable number of all orders of birds, we shall see that a means of

ready recognition of its own kind, at a distance or during rapid motion,

in the dusk of twilight or in partial cover, must be of the greatest

advantage and often lead to the preservation of life. Animals of this

kind will not usually receive a stranger in their midst. While they keep

together they are generally safe from attack, but a solitary straggler

becomes an easy prey to the enemy; it is therefore of the highest

importance that, in such a case, the wanderer should have every facility

for discovering its companions with certainty at any distance within the

range of vision.

“Some means of easy recognition must be of vital importance to the young

and inexperienced of each flock, and it also enables the sexes to

recognise their kind and thus avoid the evils of infertile crosses; and I

am inclined to believe that its necessity has had a more widespread

influence in determining the diversities of animal colouration than any

other cause whatever. To it may probably be imputed the singular fact

that whereas bilateral symmetry of colouration is very frequently lost

among domesticated animals, it almost universally prevails in a state of

nature; for if the two sides of an animal were unlike, and the diversity

of colouration among domestic animals occurred in a wild state, easy

recognition would be impossible among numerous closely allied forms.”

As examples of recognition colouration, Wallace cites, among others, the

white upturned tail of the rabbit—a “signal flag of danger,” the

conspicuous white patch displayed by many antelopes, the white marks on

the wing- and tail-feathers of the British species of butcher-birds, the

stone-chat, the whin-chat, and the wheat-ear.

Wallace therefore asserts, firstly, that recognition marks not only help

herbivorous animals to keep together, but act as a danger signal; the

member of a flock which first catches sight of the enemy takes to its

heels, displaying its white flag, which is the signal of danger to the

other members of the flock. Secondly, that recognition marks prevent the

evils of infertile crosses. Thirdly, that the necessity of being able to

recognise one another has rigidly preserved bilateral symmetry among

animals in a state of nature.

As regards assertion number one, we would point out that where a flock of

herbivora is being stalked by a beast of prey, the member of the flock

nearest to the enemy—that is to say, the hindmost member—will probably be

the first to observe him. As that creature will be more unfavourably

situated for escape than the rest of the herd, it will not be to their

advantage to follow the line it has taken. Moreover, being at the rear of

the flock, it is not in a good position to take the lead, and its pursuer

is likely to see the danger signal before its friends do. It would thus

seem that “danger signals,” while possibly sometimes of service to their

possessors, are on the whole ornaments which might profitably be

dispensed with. Natural selection can scarcely be charged with the

production of a character of such doubtful utility to the organism.

Moreover, flourishing species of many gregarious animals do not possess

any “signal flag of danger,” while, on the other hand, a great many

solitary species display markings that render them very conspicuous when

in motion. Take the case of the famous Indian Paddy Bird (_Ardeola

grayii_). This, when at rest, is coloured so as to be very difficult to

distinguish from its surroundings, but flight transforms it, for it then

displays its milk-white pinions, which would make a perfect danger

signal, if only it were not peculiarly solitary in its habits. Its

gregarious brethren, the Cattle Egrets (_Bubulcus coromandus_), on the

other hand, display no danger signal.

Interbreeding of Allied Species

That these recognition marks prevent the intercrossing of allied species

and the production of infertile hybrids appears to be pure fiction. As we

have already shown, hybrids between allied species are by no means always

infertile. Moreover, species which differ only in colour seem usually to

interbreed in those parts where they meet.

“This interbreeding,” writes Finn, on page 14 of _Ornithological and

Other Oddities_, “occurs where the carrion crow (_Corvus corone_) meets

the hooded crow (_Corvus cornix_), where the European and Himalayan

goldfinches (_Carduelis carduelis_ and _C. caniceps_) encounter each

other, and where the blue rollers of India and Burma (_Coracias indicus_

and _C. affinis_) come into contact, to say nothing of other cases.”

Of these other cases, the Indian bulbuls of the genus _Molpastes_ form a

very remarkable one. In all places where two of the so-called species

meet they appear to interbreed, and so freely do they interbreed that at

the points where the allied species run into one another it is not

possible to refer the bulbuls to either species. Thus William Jesse

writes of the Madras Red-vented Bulbul (_Molpastes hæmorrhous_) (page 487

of _The Ibis_ for July 1902): “This bird, although I have given it the

above designation, is not the true _M. hæmorrhous_. I have examined

numbers of skins and taken nests and eggs time after time, and have come

to the conclusion that our type is very constant, and at the same time

differs from all the red-vented bulbuls hitherto described. The

dimensions tally with those given by Oates for _M. hæmorrhous_, while the

black of the crown terminates rather abruptly on the hind neck, and is

not extended along the back, as is the case with _M. intermedius_ and _M.

bengalensis_. On the other hand, as in the two last species, the ear

coverts are chocolate. Furthermore, I may add—although I attach little

importance to this—that the eggs of the Lucknow bird which I have seen

are, without exception, far smaller than my eggs of genuine _M.

intermedius_ from the Punjab. My own opinion is that the Lucknow race is

the result of a hybridisation between the other three species.”

Further, in Bannu, Mr D. Donald saw _M. intermedius_ and _M. leucogenys_

paired at the same nest. That gentleman could not possibly be mistaken on

the point, as the latter species has white cheeks and yellow under

tail-coverts, while the cheeks of the former species are dark-coloured

and the patch of feathers under the tail is red. Similarly, Whitehead and

Magrath, writing of the birds of the Kurram Valley (_Ibis_, January

1909), record that the former shot no fewer than twelve bulbuls, which

undoubtedly appear to be hybrids between these two species. As these

hybrids differ considerably _inter se_, there seems no room for doubt

that they breed with one another and with the parent species.

Symmetry in Nature

Wallace’s third statement, that if the two sides of animals in a state of

nature were alike, easy recognition would be impossible among numerous

closely allied forms, reminds us forcibly of the sad case of the boy

whose tailor was his mother. _Humanum est errare_: she made her son one

pair of trousers that fastened up behind, so that the poor boy when

wearing them never knew whether he was going to or coming home from

school! If animals are able to recognise their mates, their bilateral

symmetry does not seem necessary to enable them to distinguish their

fellows from allied species.

It is, indeed, true that asymmetrically marked animals are very rarely

seen in the wild state, while they are the rule rather than the exception

among domesticated species. But this appears to be due, not to the

necessity of recognition markings in nature, but to the fact that those

animals that display a tendency to massed pigment perish in the struggle

for existence, since this massing of pigment appears to be correlated

with weakness of constitution. In other words, this massing of pigment is

an unfavourable variation, which under natural conditions dooms its

possessor. In the easier circumstances of domestication, animals which

are irregularly pigmented are able to survive, so that, among them, the

almost universal tendency to the massing of pigment can be followed

without let or hindrance.

It is unnecessary to say more upon this subject. The few facts we have

set forth suffice to destroy this particular excrescence on the Darwinian

theory.

The Colouring of Flowers and Fruits

Extremely interesting though the subject be, we are unable to consider at

length the generally accepted theory that the colour markings and

perfumes of wild flowers are the result of the unconscious selection

exercised by insects.

While not denying that many flowers profit by their colouring, that these

colours may sometimes serve to attract the insects, by means of which

cross-fertilisation is effected, we are not prepared to go to the length

of admitting that all the colours, etc., displayed by flowers and floral

structures are due to the unconscious selection exercised by insects. It

is one thing to admit that the colour of its flowers is of direct utility

to a plant; it is quite another to assert that the colour in question

owes its origin and development to natural selection. Our attitude

towards the generally accepted explanation of the colours of flowers is

similar to that which we adopt towards the theory of protective mimicry

among animals. In certain cases we are prepared to admit that the

mimicking organism derives benefit from the likeness; but this, we

assert, is no proof that natural selection has originated the likeness.

Cross- versus Self-fertilisation

The theory that flowers have developed their colours in order to attract

insects to them, and thus secure cross-fertilisation, is based on the

assumption that cross-fertilisation is advantageous to plants. It is

questionable whether this assumption is justified. True it is that

numbers of experiments have been performed, which show that, in many

cases, flowers which are artificially self-fertilised yield comparatively

few seeds. But experiments of this kind do not prove very much.

To place on the stigma pollen from the anthers of the same flower, in

case of a plant which for many generations has been cross-fertilised, is

to subject the plant in question to a novel experience—an experience

which may be compared to transplanting it to another soil. The immediate

effect may appear to be unfavourable, although, if the experiment be

persisted in, the ultimate results may prove beneficial to the plant.

That this is the case with some flowers that are artificially fertilised

is asserted by the Rev. G. Henslow. This observer states, that had Darwin

pursued his investigations further, he would probably have modified his

views regarding the benefits of self-fertilisation. Darwin’s statement

that “Nature abhors perpetual self-fertilisation” seems to be as far from

the truth as that which declares “Nature abhors a vacuum.”

From the mere fact that cross-fertilised flowers yield a greater quantity

of seed than they do when self-fertilised, it does not necessarily follow

that cross-fertilisation is advantageous. The amount of seed produced is

probably not always a criterion as to the advantages of the crossing to

the plant. Some flowers yield most seed when fertilised by the pollen

from flowers belonging to a different species!

It is significant that some plants produce cleistogamous flowers, that is

to say, flowers which invariably fertilise themselves. Such flowers never

open; so that the visits of insects are precluded.

According to Bentham, the Pansy (_Viola tricolor_) is the only British

species of _Viola_ in which the showy flowers produce seeds. The other

species are all propagated by their cleistogamous flowers. The genus

_Viola_ is an advanced species: it would therefore seem that the

production of cleistogamous flowers is an advance on the production of

entomophilous flowers. Cleistogamous blossoms are obviously more

economical.

Insects and Flowers

In the case of the malvas, epilobias and geraniums, where we see, side by

side, races of which the individuals produce insect-fertilised flowers

and those that are characterised by self-fertilised flowers, the latter

are quite as thriving as the former.

The common groundsel, which, according to Lord Avebury, is “rarely

visited by insects,” flourishes like the green bay tree, as many

gardeners know to their cost. The same may be said of the pimpernels. In

this connection it is important to bear in mind that the anemophilous, or

wind-fertilised, angiosperms, as, for example, the grasses, are believed

to be descendants of insect-fertilised or entomophilous forms.

A weighty objection to the theory that the colours of flowers have been

developed because they attract insects has been urged by Mr E. Kay

Robinson, namely, that among wild flowers the most highly coloured ones

are the least attractive to insects.

“Show me,” writes he, on page 222 of _The Country-Side_ for March 20,

1909, “the insect-collector who will seek for specimens among the

brilliant scarlet poppies. Of what use is the dog rose, with its large

discs of pinky-white, to him? On the other hand, does he not find that by

far the most attractive flowers are the almost invisible spurge laurel

blossoms in February and March, the fuzzy sallow catkins in March and

April, the bramble blossom in midsummer, and the ivy’s small green

flowers in autumn? Of these only the bramble has any pretensions to

colour, and if you try, as I have tried, the experiment of picking off

every petal from sprays of bramble blossoms you will find that its

attraction to moths does not appear diminished.

“The fact that insects do visit many conspicuously coloured flowers does

not show that the colour attracts them, when the fact is borne in mind

that they neglect others which are equally coloured, while the flowers

which they particularly haunt are inconspicuous. Conspicuous flowers

_which have abundance of nectar_ attract insects, of course, but so do

inconspicuous flowers which have nectar. If they have no nectar, neither

the conspicuous nor the inconspicuous flowers attract insects other than

pollen or petal eaters, whose visits are not good for the plant. This

shows that the nectar attracts the insects and that the colour of the

flowers makes no difference.”

In autumn many leaves assume bright and beautiful tints. These are not

believed to be in any way useful to the plant. The autumnal hues and

shades are regarded, and rightly regarded, as the garb of death and

decay. Such colours are the result of the oxidation of the chlorophyll or

green colouring matter of the leaves. Why should not the colours of the

petals of the flowers, which wither and fade long before the green leaves

do, be due to a similar cause? The bright colours of fruits are supposed

to have been effected by natural selection in order to attract

fruit-eating animals. Surely a hungry animal does not require that its

food be brightly coloured in order to find it! We must remember that

during the greater part of the year most animals have no occupation save

that of finding their food. Inconspicuously coloured fruits, like those

of the ivy, are frequently eaten by birds. The bright colours of some

ripening fruits are undoubtedly the colours of decay. Many fungi and

seaweeds have bright colours. It is never hinted that these are of any

direct utility to their possessor.

Every flower, every plant, every organism must be of some colour.

Honey

Many flowering plants produce honey. This is said by some botanists to

have been directly caused by natural selection, because the honey

attracts insects. Possibly those who take up this attitude are putting

the cart before the horse. It is probable that honey, like oxygen, is an

ordinary product of the metabolism of the plant, and that the visits of

bees and other insects to such plants are the result rather than the

cause of the honey being there. Boisier found that some plants, for

example, _Potentilla tormentilla_ and _Geum urbanum_, gave honey in

Norway, but very little near Paris.

He further discovered that by supplying certain plants copiously with

water he could induce them to produce more than their normal output of

honey.

As is their habit, Neo-Darwinians have pushed their pet theory to absurd

lengths in its application to flowers. They assert that the visits of

insects are responsible for not merely the general colour of every

flower, but also the various lines, spots, and other markings of flowers.

The lines that frequently occur on the petals are supposed to guide the

insects to the honey! This particular refinement of Neo-Darwinism, to

quote Kay Robinson, “needs little discussion. Insects have very poor

sight. You can see this when a bee or a butterfly flies bang against a

whitewashed wall; when a wasp pounces upon a black spot on a sunlit

floor, mistaking it for a fly; or when a settled dragon-fly will allow

you to poke it in the face with the end of a walking-stick, although it

will be off like a flash if you raise your arm. There is, therefore,

large reason to doubt whether insects can even see the fine lines in the

throats of flowers which are supposed to guide them to the nectar. It is

rather absurd, too, to suppose that such lines can be needed, since

insects come in swarms to inconspicuous and apparently scentless flowers

or to ‘sugared’ tree-trunks in the dark. Where there is nectar, insects

which have come to the feast from a distance need no pencilled lines to

guide them over the last quarter of an inch of their journey.”

Scents of Flowers

Neo-Darwinians further assert that the scents of flowers have been

developed by natural selection because they serve to attract insect

visitors to the flowers. In support of this contention it is urged that

the most highly scented flowers are not usually the most conspicuous

ones, since it is not necessary for a flower to be both highly coloured

and strongly scented. Again, those flowers which open at night are

usually very highly scented.

Plausible though this view seems, there are weighty objections to it.

These are so admirably summarised by Kay Robinson in the issue of _The

Country-Side_ for March 27, 1909, that we feel we cannot do better than

reproduce his words:—

“It is true that many flowers which are strongly scented are visited by

insects, but these flowers have abundance of nectar, and the insects come

in spite of the scent, and not on account of it. They visit unscented

flowers, provided that they have nectar, equally freely; and they do not

visit flowers which have scent without nectar.

“Moreover, fruits are more generally scented even than flowers; but what

explanation have those, who attribute the scents of flowers to the tastes

of insects, for the scents of fruits? Insects which visit fruits are only

robbers. Therefore, if we say that plants have scents for the purpose of

attracting insects, we accuse all plants which have scented fruits of

attempted suicide.

“There are hosts of plants, again, with scented leaves. Here also the

insects are only robbers, and it is quite clear that the scent is not

useful in attracting insects. If, therefore, you adopt the insect theory

to explain the scents of flowers, you must invent entirely new theories

to explain the scents of fruits and leaves.”

It is thus evident that the ordinarily accepted explanation of the

colours, scents, and markings of flowers is far from satisfactory.

Kay Robinson’s Theory

Mr E. Kay Robinson has put forth in recent issues of _The Country-Side_

(March 20, 27, and April 3, 1909) quite a new explanation of the

phenomena, and one which deserves careful consideration. He maintains

that “the real, primary, and original meaning of the colours, markings,

nectar and scents of flowers is not to attract insects, but to deter

grazing and browsing animals.”

“I say,” he writes, “that grazing and browsing animals avoid eating

conspicuous flowers. I have watched a flock of five hundred sheep pass

across a yard-wide strip of close-nibbled turf on the Norfolk coast,

grazing as they passed, and the number of open daisy blossoms after they

had passed seemed the same as before they came. Every one of five hundred

sheep had eaten something from that yard of grass, and not one had eaten

any of the hundred and thirty odd daisies.

“Every summer the farm horses are turned into the same old pasture, and

as the summer wanes the field always presents the same appearance—the

green grass close-grazed, the tall buttercups left standing high.

“Once, leaning over a gate with friends, I pointed out that a flock of

sheep grazing in a sainfoin field were nibbling the greenstuff close, but

were not eating the flowery stalks, when one sheep near us accidentally

pulled up a whole sainfoin plant by the roots and proceeded to munch it

upwards. Inch by inch the stem passed into its jaws, and I began to be

afraid that it was going to establish an ‘exception’ to my rule. But,

just when the bright cluster of pink sainfoin blossom was within two

inches of its teeth, it gave an extra nip, and the flower head fell to

the ground, and the sheep resumed its search for greenstuff.

“I do not say that this would always happen—I should be sorry for any

theory which depended upon the intelligence of a sheep—but it was a very

striking object-lesson to my two companions; and any one who looks around

during this summer with an inquiring mind will find plenty of evidence

that grazing, browsing, and nibbling animals avoid flowers, and stick to

greenstuff when they can get it.

“I do not say that all animals avoid the same flowers. Horses, for

instance, may dislike large flowers like roses and conspicuous yellow

flowers like buttercups, but they will bite off flat clusters of minute

white or pale yellow flowers, such as yarrow or wild parsnip. These

distinctions made by certain kinds of beasts will probably in the future

be found to afford valuable evidence as to the regions of origin of our

flowers and animals. Such plants as the yarrow and the wild parsnip, for

instance, probably did not originate in the home of the wild horse,

because they are not protected against it.

“As a general rule, however, there is abundance of evidence that plants

with conspicuous flowers gain a large advantage in the struggle for

existence, because grazing and browsing animals avoid them; while there

is no real evidence at all that conspicuous flowers attract insects.”

Kay Robinson extends this explanation to the shape, the scent, and the

nectar of flowers. He admits that many flowers are adapted to the visits

of insects, but this is, he asserts, but a secondary result. The “real,

primary meaning” of the shapes of flowers of curious configuration is, he

insists, “a deterrent to grazing or browsing animals.”

According to him plants, like the snap-dragon, which have “blossoms in

the semblance of a mouth,” are avoided by grazing animals, because they

mistake such flowers for mouths, and have no wish to be bitten! Orchids,

he asserts, “are strongly deterrent to grazing and browsing animals,

which are looking for greenstuff, and regard these gaudy, spidery, winged

blossoms as live creatures.” “If this is not the truth,” he asks, “will

any adherent of the theory that we owe the shapes of flowers to insects

explain why some of our common British orchids are so like bees, spiders,

etc.? Some which have no particular resemblance to any insect still

exhibit weird shapes, suggestive to the human mind of living things, such

as lizards, etc. The reason why they look like bees, spiders, lizards,

and various unclassed creatures is quite simple. Grazing animals are

looking for greenstuff, and do not wish to eat living creatures which may

bite or sting or taste nasty. Thus the orchids have acquired the power of

looking like creatures.

“Every one,” he continues, “who is familiar with the blossom of the wild

carrot—a flat head of minute, dull-white blossoms—must have noticed how

very often the centre blossom in each head is purplish or reddish-black.

This makes it very conspicuous in the middle of the flat white flower

head. Now what conceivable use can this barren little blackish

blossom—scarcely bigger than a pin’s head—be to the wild carrot plant if

we regard the flat head of white flowers as an attraction to the sight of

insects? If, on the other hand, we rightly regard the flat head of white

blossoms as an advertisement to grazing animals that it is not wholesome

greenstuff, but innutritious blossoms liable to be infested with ants and

other stinging insects, we see at once the great use of this small

blackish flower in the middle. It looks like an insect, and possibly in

the home of the wild carrot there is some minute blackish insect with a

peculiarly villainous smell or taste—or perhaps a potent sting—which

grazing animals carefully avoid whenever they can see it. Thus the wild

carrot flourishes; though here in Britain—where the wild carrot has

established itself now—we may fail at first to see the exact meaning of

the trick. I think, however, that, when we understand it, it fits

admirably into the theory that the shapes and colours of flowers are

primarily useful as deterrents to grazing and browsing animals and not as

attractions to insects.

“Thus we see,” he concludes, “that the queer shapes of these orchids,

which are a great stumbling-block in the way of those who preach that we

owe the shapes of flowers to the tastes of insects, become a strong

confirmation of my theory that we owe the shapes of flowers to grazing

and browsing animals.”

Of the nectar of flowers, Kay Robinson writes: “Since this is eagerly

sought for by hosts of insects, whose visits are in most cases useful to

the flowers, it seems only natural to suppose that we see cause and

effect in this connection.

“Here, however, I will outline my theory of the origin of nectar and of

flowers in general.

“I think there is no doubt whatever that all the parts of a flower are

modified leaves. The original type of flowering plant—I think we may

safely assume—had a single stem and produced its seed at the summit, as

the crown of its year’s endeavour. The flower, before it became what we

would recognise as a flower, was a cluster of protecting leaves round the

seed-making parts of the plant. To the production of the seed the whole

energies of the plant were devoted, and into the cluster of leaves at the

top of the stem all the essences of the plant were concentrated. If

during the coming spring you handle and examine the leaves at the end of

the strong shoots of thorns or fruit bushes, you will find that the

surface of the young leaves is quite sticky. If you observe browsing

animals also, you will discover that—contrary to expectation—they do not

like strong-growing, juicy shoots, evidently preferring mature leaves

lower down the branch. This shows, I think, that plants have the power of

protecting their new shoots by crowding into them the volatile oils and

essences which they produce as a protection against animals. Now nectar

appears always to be distasteful to grazing and browsing animals; and

they also dislike scented flowers. I think, therefore, that it is

reasonable to suppose that the nectar and scents which now distinguish so

many flowers were first produced as an exudation of concentrated sap upon

the surfaces of the protecting leaves round the seed-making parts of the

original flowers. As these leaves became more efficiently protective by

assuming colours, shapes, and markings which warned animals of their

character, so their apparatus for producing scent and honey became

specialised; and at this point the insect appeared upon the scene as a

factor in the life’s success of the plant.”

Such, then, is Kay Robinson’s bold and original theory. In some respects

it seems far-fetched. The natural inclination is to ask, “Is it possible

that cattle can be so stupid, so blind, as to really believe that a

snap-dragon is the mouth of an animal, or that an orchid is a spider?”

At present we know so little of animal psychology that we are not yet in

a position to give an answer to this question. Horses, we know, are apt

to be frightened by the most harmless things, such as a piece of brown

paper lying on the road. Mr Robinson’s theory should give a stimulus to

the study of the mind of animals—a study which, if properly undertaken,

will probably throw a flood of light upon some of the problems of

evolution. Mr Robinson’s theory equally with the ordinarily-accepted

hypothesis, utterly fails to explain the first origins of colours,

scents, etc. When once a flower has acquired a certain amount of colour,

it is easy to understand how that flower may attract insects or repel

grazing animals. But how can the origin of the colour or other

characteristic be explained?

We asked Mr Kay Robinson how he would account for the great success in

the struggle for existence of some species of grasses on which

herbivorous animals feed so largely. He replied, in the issue of _The

Country-Side_, dated April 3, 1909:—

“The grass has a manner of growth which defies the grazing animal. Its

long, thin leaves are constantly pushing upwards from the ground, and, if

they are grazed down one day, they will have pushed up again the next.

Moreover, when the outside blade of grass has exhausted its power of

growing, there is another blade inside it with many inches still to grow,

and another inside that which has scarcely begun to grow, and yet another

further in which has not yet seen daylight; and so on. In a state of

nature grazing animals are nowhere so numerous on any given patch of

ground from day to day as to keep down the grass. If they were,

carnivorous animals would stay there to eat the grazing animals, and grow

fat and multiply. Thus the grazing herds are scattered and wandering,

followed wherever they go by the beasts of prey; and in their absence the

grass pushes ahead, so that when the grazing animals return its clump is

larger and its roots are stronger, and it is better able to survive

attack than before.

“The method of the clovers and trefoils is quite different. When

circumstances are favourable and enemies few, they will form large-leaved

luxuriant clumps, with fine heads of blossom; but where grazing animals

abound they have the power of adapting themselves to altered

circumstances. They creep so closely along the ground that the teeth of

the grazing animal cannot pick them up between the surrounding grass, and

they produce leaves so small and short-stalked that to eat them would be

like nibbling the pile off velvet. Any clover or trefoil thus growing in

self-defence is accepted as the ‘shamrock’ of Ireland; and it is

certainly a fine emblem for a race which regards itself as surviving in

spite of incessant oppression.

“These are the reasons, however, why the grasses and clovers or trefoils

continue to enrich old pastures when most of the other plants disappear,

with the exception of daisies and buttercups, and the acid sorrels.”

We should be glad to hear how Mr Robinson accounts for the conspicuous

flowers in the species of “prickly pear” (_Euphorbia_), which is so

abundant in India, and which is not browsed upon by animals.

We regret that we are not able to devote more space to this most

interesting theory. We can only add that, even if it fail to become

widely accepted, it is of great value as showing that it is possible to

offer a plausible explanation of a large number of phenomena, which nine

out of ten botanists explain in a very different way.

So satisfied are the majority of naturalists with the “insect theory,”

that they seem of late years to have paid but little attention to the

subject of floral colouration. This affords a striking instance of the

pernicious influence which Neo-Darwinism is exercising on the minds of

men to-day. It tends to stifle research instead of stimulating it.

Accepted Theories Unsatisfactory

We have now dealt with the theory of protective colouration, the theory

of warning colouration, the theory of mimicry, and the theory of

recognition markings. We have shown that although many organisms

undoubtedly derive profit from the fact that they are difficult to see in

their natural surroundings or from their resemblance to other organisms,

the hypothesis that this inconspicuousness or the mimicry of these

animals has been caused by the natural selection of small variations is

untenable.

Warning colours, we have shown, although a disadvantage to their

possessors, are sometimes seen in nature because they are accompanied by

unpalatability. The theory of recognition markings must, we fear, be laid

to rest in the burial ground of exploded hypotheses.

The extreme popularity of the existing theories regarding animal

colouration and their very general acceptance are to be attributed,

firstly, to their simplicity; secondly, to the fact that they have thrown

light on many phenomena which previously had seemed inexplicable;

thirdly, that if we assume, as the great majority of biologists do, that

evolution has been effected by the accumulation of numerous variations,

small in degree and indefinite in direction, we seemed forced either to

accept Neo-Darwinism or admit that the whole subject of animal

colouration baffles us, in other words, to reject what appears like

cosmos and substitute for it chaos.

With a few exceptions, books that deal with the colours of organisms,

while emphasising the evidence in favour of the generally-accepted

theories, seem almost entirely to ignore the host of facts that do not

appear to fit in with them.

This is largely due to the almost unavoidable bias of the human mind when

obsessed by a pet theory. There are none so blind as those who will not

see. It is also, in part, the consequence of the prevalent neglect of the

scientific method of comparison which leads men to theorise on

insufficient evidence. This, of course, is a natural result of

specialisation in biology. Naturalists are in the habit of confining

their study to the habits of the animals of one particular country and

then making far-reaching generalisations therefrom.

As an example of the kind of theorising to which this method leads, we

may cite the often-quoted theory which ascribes the green colouring of

some arboreal fruit-eating pigeons to adaptation to an existence among

tropical foliage, and ignores the fact that in America tree-haunting

pigeons are never of this colour, and that it is not by any means

universal even among the old-world pigeons.

White Down of Nestlings

Similarly, a theory has been advanced (W. P. Pycraft, _Knowledge_, 1904,

p. 275) that the white down of some nestling birds, is an adaptation to

resisting the heat of the sun in open nests. This is at once negatived by

the fact that young owls, usually hatched in shaded places, are also

generally white, while young cormorants, living in open nests, are black;

yet the allied darters, with the same breeding haunts in some cases, have

white young. Lest it should be thought that black has some especial value

in a nestling living exposed, we may mention that young petrels, which

are born in holes, have black or dark down.

As we have already pointed out, naturalists in too readily accepting the

theory that variation is minute in degree and indefinite in direction,

have raised quite unnecessary difficulties, even for the selection

hypothesis. We have cited certain facts, which seem to show that

variations, as a rule, are not indefinite in direction; of these the most

striking is furnished by birds in which the tail feathers are greatly

elongated. Were variations indeterminate, we might reasonably expect to

find that the elongation occurred in one particular feather or pair of

feathers in one species, in another pair in a second species, in a third

pair in a third species, and so on. But this is not the case; no bird has

one _single_ long feather in its tail, and when two are elongated, as is

so commonly the case, these are almost invariably the middle or the

outside pair; _e.g._, in the European bee-eater and pheasant it is the

former, in the swallow and blackcock, the latter.

Exceptions are so rare that they may almost be said to prove the rule;

_e.g._, although most terns have the outer-tail feathers elongated, in

some of the Noddy Terns (_Anous_, _Gygis_) the third pair, in others the

fourth pair, of tail feathers are the longest. This must mean one of two

things, either that the variation, as regards length in tail feathers,

other than middle or outer, does not ordinarily occur, or that it occurs,

but is, in some way, inimical to the welfare of the species. The latter

hypothesis does not seem probable, as the Noddies are particularly

abundant birds where they occur, that is to say, in the tropical seas;

therefore, we can only conclude that that particular variation has not

occurred in birds as a whole.

We have adduced abundant evidence to show that mutations or discontinuous

variations occur in nature; and as these afford much more favourable

material on which natural selection can act, it is reasonable to suppose

that they have played a considerable part in evolution.

When discussing the phenomena of inheritance, we attempted to show that,

not improbably, these discontinuous variations are due to some

re-arrangement in the constituent parts of the unit characters, or

biological molecules, as we have called them.

Cranes

In this connection we may mention the apparently singular phenomenon of

different species in the same natural group, exhibiting either a definite

excess or deficiency of plumage on the head. Among cranes, most species

are more or less bald; but the Demoiselle (_Anthropoides virgo_) has a

fully-feathered head with long side-plumes, while the head of the Stanley

Crane (_A. paradisea_) appears to be swollen, so abundantly is it

feathered. The crowned cranes, although bare-cheeked, have double crests,

the two parts of which have been respectively compared to a pen-wiper and

a bunch of toothpicks!

Among the guinea-fowls, several species are crested, while others, as,

for example, the domestic one, are bare-headed. Now, on the theory of

evolution, by accumulation of minute variations, phenomena such as these

are difficult of explanation; but, on the assumption that a slight

rearrangement of the biological atoms in the molecule may produce very

diverse results, as we see in the case of chemical molecules, and of

seasonally dimorphic butterflies, there is no particular ground for

surprise at such a phenomenon.

In this connection we may cite the significant fact, so well known to

canary breeders, that two crested birds when mated tend to produce a

bald-headed one.

If the colour of any part of an organism be due to the internal

arrangement of the constituent parts of the biological molecule from

which it is derived, we should expect any rearrangement of the component

parts to produce quite a different colour. In other words, we should

expect occasionally to see colour-mutations. These are precisely what we

do see. Similarly, if the scheme of colouring of an organism be due to a

certain grouping of biological molecules, we should expect the same

scheme of colouring to occur in organisms which are not nearly related.

This, too, we observe in nature.

Many of the phenomena of mimicry, and all the cases which we have cited

as pseudo-mimicry, seem to us to be referable to this.

Magpie Colouring

Take, for example, the magpie colouration in birds—that is to say, a

scheme of colouring in which the body is white, and head, wings, and tail

black. This occurs in the following birds belonging to the most diverse

groups:—

The Magpie.

The Magpie Tanager (_Cissopis leveriana_).

The Magpie Robin (_Copsychus saularis_), cock only; in the hen the black

is replaced by brownish grey.

The Pied Honeyeater (_Entomophila picata_).

The Chaplain Crow (white-bodied form of the hoodie crow).

The New Ireland Swallow Shrike (_Artamus insignis_).

The Magpie Goose (_Anseranas melanoleucus_).

Combinations of this kind, in which the black is replaced by brown or

grey, are excessively rare.

On the other hand, we see in several birds the combination in which the

white is replaced by yellow:—

The Common Troupial (_Icterus vulgaris_).

The Black-headed Oriole (_Oriolus melano cephalus_).

The Black-and-yellow Grosbeak, male only.

What we may call imperfect magpie colouration, _i.e._ where the head

becomes white, occurs in several species of birds. The head of a black

species sometimes becomes white as a mutation; in the domestic Muscovy

duck, for example, an individual is sometimes produced having a white

head, although the black of the remainder of the plumage remains

unchanged.

As examples of this scheme of colouration we may cite—

Black-and-white Fruit Pigeons (_Myristicivoræ_).

Several Gannets (_Sula capensis_, _S. serrator_, etc.)

Swallow-tailed Kite (_Elanoides furcatus_).

Several Storks (_Euxenura maguari_, _Anastomus oscitans_, _Pseudotantalus

cinereus_).

Moreover, a common variety of the barn-door fowl has also a white body

and black primaries and tail, showing that this scheme of colour may

arise as a mutation.

A further elimination of black in the tail and body leads us to white

birds with more or less black wings:—

White Storks (_Ciconia alba_, _C. boyciana_, and _Euxenura maguari_).

The White Crane (_Grus leucogeranus_).

The Snow Geese (_Chen nivalis_, _C. rossi_).

The Common Gannet (_Sula bassana_).

The White Buzzard (_Leucopternis_).

The Scavenger Vultures (_Neophron_).

A recurring combination in mammals is black, with a white marking on the

breast.

Most of the bears, even young brown bears, show a tendency to this. It is

also found in the Tasmanian devil, and in varieties of our domestic cats,

rats, and dogs; also in the domestic duck.

The white-spotted pelage, not uncommon in deer, especially fawns, is

curiously repeated in the Australian carnivorous marsupials, known as

Native Cats (_Dasyurus_).

In domestic animals we frequently find the following localisation of

white—white socks, collar, breast, and muzzle. The arrangement occurs in

cats, dogs, rabbits, guinea-pigs and mice, also in the horse and pig, but

without the collar. The arrangement is not seen in goats, cattle, or

sheep, nor in wild animals of any kind. This would lead to the conclusion

that the combination is correlated with some character unfavourable to

survival under natural conditions.

Many variations which frequently occur among both wild and domestic

animals do not persist in nature.

Albinos

As instances of such variations we may mention pure albino forms, that is

to say those in which pigment does not occur in the eyes.

It is easy to see why this variation is not allowed to persist in nature.

Its possessors are handicapped by bad eyesight, and so have no chance of

surviving in the struggle for existence. It is thus that natural

selection acts. On the other hand, white species with pigmented eyes are

fairly numerous. These enjoy normal eyesight, but labour under the

disadvantage of being easily seen by their foes. Hence we find that white

species generally either occur in a snowy habitat, or are powerful and

both able and ready to defend themselves. In this connection it is

interesting to notice that in New Zealand all birds, whether introduced

or indigenous, are particularly liable to albinism. Owing to the fewness

of their enemies these albinistic forms are able to persist.

A variation, or rather a mutation, that frequently occurs among

domesticated birds, but which is seen in very few wild species, is that

which takes the form of white primary feathers on the wing. This

variation must often occur in nature, but it rarely establishes itself,

apparently because white feathers do not resist wear so well as coloured

ones do.

Biological Molecules and Colour

Black-and-yellow colouration occurs in several widely separated species

of birds. The arrangement of the two colours follows to some extent the

same rules as the black-and-white combination.

Several birds have a yellow body with black head, wings, and tail, such

as—

The Black-headed Oriole (_Oriolus melanocephalus_).

The Black-and-Yellow Grosbeaks (_Pycnorhamphus icteroides_, _P. affinis_)

(cock).

The Common Troupial (_Icterus vulgaris_).

In others the black on the head is nearly or quite suppressed, that on

the tail remaining to a greater or less extent; such are—

The Golden Orioles (_Oriolus galbula_, _O. kundoo_, etc.).

Several species of _Icterus_.

Several fly-catchers of the genus _Piezorhynchus_ (males only).

[Illustration: BRAZILIAN TROUPIAL]

[Illustration: INDIAN BLACK-HEADED ORIOLE]

We have said sufficient to show that certain combinations of colours

recur in nature in species which are neither nearly related to one

another nor subjected to similar environment. For such phenomena it is

difficult, if not impossible, to account on the theory that natural

selection, acting on minute variations, is responsible for all the varied

colouring of the animal kingdom. The facts, however, are in accordance

with the supposition that the organism is the result of the growth and

development of a number of units or biological molecules which exist in

the fertilised egg.

If there be any truth in the supposition, the colouration of every animal

must be due to the development of one or more of these molecules.

Colouration may be expression of the arrangement of all the molecules in

the fertilised egg, or it may be due to the development of a number of

molecules whose function is to determine the colouring of an organism, or

it may be the result of the development of one such molecule, which

perhaps splits up in such a way that a portion attaches itself to each of

the other molecules.

But it is idle to speculate on this point. As we have already insisted,

the tendency to build up elaborate theories on very slender foundations

is a too frequent failing of zoologists. We desire merely to emphasise

the fact that the phenomena of animal colouration almost force us to the

conclusion that the colouring of each organism is the result of the

development of a number of units.

It may be objected that, if this be the case, the number of the units

which contribute to the colour of any organism must be exceedingly large,

since we see in nature an almost limitless number of different schemes of

colouring. If the colour of each animal be the result of the development

of a few units, it might be thought, firstly, that the diversity of

schemes of colouration which we observe in nature could not possibly

occur; and secondly, that, under such circumstances, the colour pattern

of a bird or beast should be of the nature of a mosaic, each colour being

sharply defined and separated from every other colour, instead of the

colours shading one into the other, as is so frequently the case.

Such objections would be based on a misconception as to the nature of the

units which combine to produce the colouration of an organism. _These

units show themselves as centres of development of colour_, as points

from which the colour or colouring they represent spreads, until it meets

and mingles with other patches of colour which are being developed from

other centres. The colour produced at one centre may spread more rapidly

than that which forms at another; this, of course, will result in a

preponderance in the organism of the colour which is produced at the

former centre.

Further, we must bear in mind that the development of each

colour-producing unit is largely affected by conditions external to it,

as we shall see when dealing with Sexual Dimorphism.

More than one naturalist, who has paid careful attention to the subject

of animal colouration, has perceived that through the apparently endless

diversity of the colouring of organisms something like order runs.

Mr Tylor Quoted

Over thirty years ago Mr Alfred Tylor called attention to this important

fact. That observer, whose views met with the approval of Wallace, was of

opinion that colour follows structure, and that in a many-hued animal it

changes at points where the function changes.

“If,” writes Mr Tylor, “we take highly decorated species—that is, animals

marked by alternate dark or light 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 eyes are

emphasised in colour.”

More recently Mr J. Lewis Bonhote has devoted much attention to this

important subject. The results of his researches are summarised on page

185 of vol. xxix. of the _Proceedings of the Linnæan Society_, and on

page 258 of the _Proceedings of the Fourth International Ornithological

Congress_, 1905. Mr Bonhote states that the presence or absence of colour

tends almost invariably to make its appearance, first of all, on certain

definite tracts, common to mammals and birds alike, which he calls

_pœcilomeres_.

Pœcilomeres

“Pœcilomeres,” he writes, “are situated on the following parts, viz.,

chin, malar stripe, maxillary stripe, a spot above and slightly in front

of the eye, a spot below or slightly behind the eye, the ear, crown of

the head, occiput, fore-end of sternum, vent, rump, thighs, wrist,

shoulders (above and below).

“Now, there is hardly any species of bird on which one or more of these

pœcilomeres is not ‘picked out’ (to use a painter’s expression) in some

colour different from that of the surrounding parts, and, in fact, most

of the so-called recognition or protective markings will be found on

these patches.

“On the other hand, among many species the differentiation of colour on

the pœcilomeres is not so conspicuous as to attract the eye or to serve

in any way for protection or mimicry, _yet we still find them marked by

differences of colour so slight that, unless especially looked for, they

would never be noticed_.

“Or, again, some species occasionally, but not invariably, show a few

white feathers on certain parts of their body, and, when such is the

case, it will be found that these white feathers appear on the

pœcilomeres. . . . There is hardly a species in which examples of these

pœcilomeres may not be found. . . . The Kingfisher (_Alcedo ispida_)

shows the various head pœcilomeres very clearly, and as examples of

inconspicuous differences on these tracts, the rump of the hen sparrow

(_Passer domesticus_) and hen chaffinch (_Fringilla cœlebs_), the malar

stripe and dark ear-patch of the hen Yellow Bunting (_Emberiza

citrinella_), and the dark ante-orbital patch of the Barn Owl (_Strix

flammea_) are familiar examples. And, lastly, as an instance of the class

where a few white feathers frequently, but not invariably, appear, the

young of the cuckoo (_Cuculus canorus_) forms a good example.

“These spots may, however, appear in a transitory manner, as, for

instance, where a change of plumage (not necessarily moult) is

occurring.”

As an instance of this, Bonhote cites the case of a young male Shoveler

(_Spatula clypeata_), “in which the metallic colour on the head first

showed itself on the post-orbital and auricular pœcilomeres, gradually

meeting and joining up across the head with the crown and occipital

pœcilomeres, and then finally spreading forwards. And it may be well to

note that the joining up of the auricular and post-orbital pœcilomeres

formed a metallic patch similar in size and position to that found in the

male Teal (_Querquedula crecca_), and, further, in the last stage, when

the whole head, except the portion round the beak, was metallic, the

markings are similar to those found permanently in the hen Scaup

(_Fuligula marila_).

“Now, these resemblances taking place in the normal pure-bred wild

shoveler, the question of reversion does not come in, and no one would

suppose these resemblances due to anything more than transitional

variation, and it is the object of this portion of the paper to show that

variation in colour follows along definite lines.”

Biological Molecules

Mr Bonhote continues: “As a further illustration of how widely spread

these lines are throughout the mammalian and avian kingdoms, we may note

the assumption of the brown head in the case of the Black-headed Gull

(_Larus ridibundus_), which invariably follows each year on lines similar

to those related in the case of the shoveler, and . . . the method by

which, on the approach of winter, the stoat assumes his white dress, is

(although the change is from brown to white) again conducted along

precisely similar lines.” Mr Bonhote argues with great force that, as the

process occurs in two animals so widely separated, the fundamental cause

must be a deep-seated one. There can be no doubt that these pœcilomeres

of Bonhote are connected with our biological molecules. Each of these

pœcilomeres is the result of the development of one of these unit

characters; each is to be regarded as the centre of activity, the sphere

of influence of a biological molecule, or the portion of one, which

controls the colouring of a definite region of the organism. In the case

of creatures which display the same colour throughout, these molecules

all give rise to the same kind of colouring; in the case of animals which

display a variety of colours and markings the various molecules give

origin to various colours. But we must bear in mind that the final colour

to which each colour-producing molecule gives rise depends to some extent

on circumstances other than the constitution of the molecule. Thus it is

that the young in most organisms differ in colour and marking from the

adults. On this also depends the phenomena of seasonal and sexual

dimorphism. The same colour-producing molecule may give rise to one

colour under one set of conditions and to a totally different colour

under another set of conditions.

It is a significant fact that under abnormal conditions the feathers of

birds tend to disappear precisely on those spots where the pœcilomeres of

Bonhote occur.

Thus in a sickly cage bird the feathers frequently show a tendency to

fall off on the following spots: crown of head, lores, jaws, head

generally, rump, vent and thighs.

Many wild birds—as, for example, the cranes—display patches of naked skin

on the head, and these are usually situated on pœcilomeres. Similarly,

natural excessive developments of plumage tend to occur on the

pœcilomeres, or, rather, the spots characterised by pœcilomeres—for

example, the train of the peacock. Loral plumage, it is true, is seldom

long, but is often of a peculiar nature.

Colour mutations tend to occur on the pœcilomeres. Thus it is that these

pœcilomeres often form the distinctive characters and markings of allied

species. This is precisely what we should expect if the pœcilomeres

correspond to biological molecules and mutations are the result of the

rearrangement of the constituent parts of these molecules.

Still more significant is the fact that the colour-markings in hybrids

tend to follow pœcilomeres.

Bonhote has performed a large number of experiments in hybridising ducks.

Some of his hybrids were produced from three pure ancestors, as, for

example, the pintail, the spotbill, and the mallard; others from two

ancestors. Some of these hybrids were crossed with other hybrids, and

others with the parent forms, hence Bonhote secured a number of hybrids,

each of which had a distinctive appearance; but _all_ the variations

appearing among the hybrids were found to start on one or more of the

pœcilomeres.

Certain of the hybrids showed a resemblance to one or other of the parent

species, others were unlike either parent, and resembled either no known

species or species other than their parents.

When a hybrid shows a resemblance to a species other than that to which

either parent belongs, it is said to exhibit the phenomenon of atavism or

reversion,—the individual is supposed to have been “thrown back” to an

ancestral form.

The true explanation of the phenomenon would seem to be that, as the

result of the crossing, biological molecules in the fertilised egg have

been formed which, on development, give rise to combinations of colour

like those seen in other species.

Thus the phenomena of “mimicry” and “reversion” are, we believe, due to

the fact that in the fertilised egg of both the pattern and its copy a

similar arrangement of biological molecules obtains. If we regard the

sexual act as resembling in many respects a chemical synthesis, the

phenomenon need not surprise us.

To sum up, the observed facts of animal colouration seem to indicate that

there are in each organism some twelve or thirteen centres of colouring,

which we suggest may correspond with portions of the fertilised egg. From

each of these centres the colour develops and spreads, so that every part

of the organism is eventually coloured. These centres of colouring are

not altogether independent of one another. Sometimes they all give rise

to the same hue, in which case we have a uniformly-coloured organism,

such as the raven. More often from some one colour develops, and from

others another colour; if these two colours happen to be black and white,

the result is a pied organism, which displays a definite pattern due to

the correlation of the various colour-producing biological molecules.

Thus it occasionally happens that two widely different organisms exhibit

very similar markings, and therefore resemble one another. When this

resemblance is believed to be of advantage to one or other of the

similarly-coloured species, naturalists call it mimicry, and assert that

the likeness is due to the action of natural selection; but where neither

organism can profit by the resemblance, zoologists make no attempt to

explain it. What we suggest is that the colouration of an animal depends

upon the structure, or, at any rate, the nature, of the parts of the egg

which produce these centres of colour. But this is not by any means the

only cause that determines the colouration of the organism. If it were,

young creatures in their first plumage would invariably resemble the

parents, the two sexes would always be alike, and there would be no such

phenomenon as seasonal dimorphism.

As a matter of fact, the portions of the egg (we call them, for the sake

of clearness, colour-producing biological molecules) which give rise to

the pœcilomeres exhibit themselves merely in the shape of tendencies; the

ultimate form the colouring will take depends to a large extent upon

other and extraneous circumstances, such as the secretion of hormones.

Thus it is that organisms seem to display an almost endless diversity of

colouration. But beneath all this diversity we see something like order.

It occasionally happens (_why_, we do not know) that one, or more, of the

biological molecules which make up the nucleus of the fertilised ovum

becomes altered in the sexual act, with the result that a discontinuous

variation or mutation appears in the resulting organism. The mutation may

be a favourable one, or one which does not affect in any way the chances

of an organism in the struggle for existence, or an unfavourable one. In

the last of the three cases the organism will perish early and not leave

behind any offspring exhibiting its peculiarity.

It is thus that natural selection acts. Natural selection weeds out

relentlessly all organisms which display unfavourable variations. It is

thus obvious that many species may, and we believe do, exist which

possess characters of no direct utility to them, or even slightly harmful

ones. For this reason Wallace and his followers fail in their attempts to

prove that every patch of colour in every organism is of direct utility.

Natural selection has to take an animal as it finds it—the good with the

bad. If an organism as a whole is not wanting—that is to say, if it is

able to hold its own against other organisms, and is fitted to fill any

place in nature—that organism will probably survive, although it may be

defective in many respects. As its name implies, natural selection is a

mere selecting agency. It has to choose from what is presented to it. It

is not, as many seem to think, a manufacturer or inducer of variations.

Natural selection can no more _make_ an animal vary in any given

direction than the human breeder can. Its power is limited to the

destroying of all variations which do not pass the test prescribed by it.