On the Genesis of Species

S >> St. George Mivart >> On the Genesis of Species

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After endeavouring to explain some of the facts in a way to be noticed
directly, Mr. Wallace adds:[64] "But even the conjectural explanation now
given fails us in the other cases of local modification. Why the species of
the Western Islands should be smaller than those further east; why those of
Amboyna should exceed in size those of Gilolo and New Guinea; why the {85}
tailed species of India should begin to lose that appendage in the islands,
and retain no trace of it on the borders of the Pacific; and why, in three
separate cases, the females of Amboyna species should be less gaily attired
than the corresponding females of the surrounding islands, are questions
which we cannot at present attempt to answer. That they depend, however, on
some general principle is certain, because analogous facts have been
observed in other parts of the world. Mr. Bates informs me that, in three
distinct groups, Papilios, which, on the Upper Amazon, and in most other
parts of South America, have spotless upper wings, obtain pale or white
spots at Para and on the Lower Amazon, and also that the AEneas group of
Papilios never have tails in the equatorial regions and the Amazon valley,
but gradually acquire tails in many cases as they range towards the
northern or southern tropic. Even in Europe we have somewhat similar facts,
for the species and varieties of butterflies peculiar to the Island of
Sardinia are generally smaller and more deeply coloured than those of the
mainland, and the same has been recently shown to be the case with the
common tortoiseshell butterfly in the Isle of Man; while _Papilio
Hospiton_, peculiar to the former island, has lost the tail, which is a
prominent feature of the closely allied _P. Machaon_.

"Facts of a similar nature to those now brought forward would no doubt be
found to occur in other groups of insects, were local faunas carefully
studied in relation to those of the surrounding countries; and they seem to
indicate that climate and other physical causes have, in some cases, a very
powerful effect in modifying specific form and colour, and thus directly
aid in producing the endless variety of nature."

[Illustration: OUTLINES OF WINGS OF BUTTERFLIES OF CELEBES COMPARED WITH
THOSE OF ALLIED SPECIES ELSEWHERE.

Outer outline, _Papilio gigon_, of Celebes. Inner outline, _P. demolion_,
of Singapore and Java.--2. Outer outline, _P. miletus_, of Celebes. Inner
outline, _P. sarpedon_, India.--3. Outer outline, _Tachyris zarinda_,
Celebes. Inner outline, _T. nero_.]

With regard to butterflies of Celebes belonging to different families, they
present "a peculiarity of outline which distinguishes them at a glance from
those of any other part of the world:"[65] it is that the upper wings {86}
are generally more elongated and the anterior margin more curved. Moreover,
there is, in most instances, near the base an abrupt bend or elbow, which
in some species is very conspicuous. Mr. Wallace endeavours to explain {87}
this phenomenon by the supposed presence at some time of special
persecutors of the modified forms, supporting the opinion by the remark
that small, obscure, very rapidly flying and mimicked kinds have not had
the wing modified. Such an enemy occasioning increased powers of flight, or
rapidity in turning, he adds, "one would naturally suppose to be an
insectivorous bird; but it is a remarkable fact that most of the genera of
fly-catchers of Borneo and Java on the one side, and of the Moluccas on the
other, are almost entirely absent from Celebes. Their place seems to be
supplied by the caterpillar-catchers, of which six or seven species are
known from Celebes, and are very numerous in individuals. We have no
positive evidence that these birds pursue butterflies on the wing, but it
is highly probable that they do so when other food is scarce. Mr. Bates
suggested to me that the larger dragon-flies prey upon butterflies, but I
did not notice that they were more abundant in Celebes than elsewhere."[66]

Now, every opinion or conjecture of Mr. Wallace is worthy of respectful and
attentive consideration, but the explanation suggested and before referred
to hardly seems a satisfactory one. What the past fauna of Celebes may have
been is as yet conjectural. Mr. Wallace tells us that now there is a
remarkable _scarcity_ of fly-catchers, and that their place is supplied by
birds of which it can only be said that it is "highly probable" that they
chase butterflies "when other food is scarce." The quick eye of Mr. Wallace
failed to detect them in the act, as also to note any unusual abundance of
other insectivorous forms, which therefore, considering Mr. Wallace's zeal
and powers of observation, we may conclude do not exist. Moreover, even if
there ever has been an abundance of such, it is by no means certain that
they would have succeeded in producing the conformation in question, for
the effect of this peculiar curvature on flight is by no means clear. We
have here, then, a structure hypothetically explained by an uncertain {88}
property induced by a cause the presence of which is only conjectural.

Surely it is not unreasonable to class this instance with the others before
given, in which a common modification of form or colour coexists with a
certain geographical distribution quite independently of the destructive
agencies of animals. If physical causes connected with locality can
abbreviate or annihilate the tails of certain butterflies, why may not
similar causes produce an elbow-like prominence on the wings of other
butterflies? There are many such instances of simultaneous modification.
Mr. Darwin himself[67] quotes Mr. Gould as believing that birds of the same
species are more brightly coloured under a clear atmosphere, than when
living on islands or near the coast. Mr. Darwin also informs us that
Wollaston is convinced that residence near the sea affects the colour of
insects; and finally, that Moquin-Tandon gives a list of plants which, when
growing near the sea-shore, have their leaves in some degree fleshy, though
not so elsewhere. In his work on "Animals and Plants under
Domestication,"[68] Mr. Darwin refers to M. Costa as having (in _Bull. de
la Soc. Imp. d'Acclimat_. tome viii. p. 351) stated "that young shells
taken from the shores of England and placed in the Mediterranean at once
altered their manner of growth, and formed prominent diverging rays _like
those on the shells of the proper Mediterranean oyster_;" also to Mr.
Meehan, as stating (_Proc. Acad. Nat. Sc. of Philadelphia_, Jan. 28, 1862)
"that twenty-nine kinds of American trees all differ from their nearest
European allies in _a similar manner_, leaves less toothed, buds and seeds
smaller, fewer branchlets," &c. These are striking examples indeed!

But cases of simultaneous and similar modifications abound on all sides.
Even as regards our own species there is a very generally admitted opinion
that a new type has been developed in the United States, and this in about
a couple of centuries only, and in a vast multitude of individuals of {89}
diverse ancestry. The instances here given, however, must suffice, though
more could easily be added.

[Illustration: THE GREAT SHIELDED GRASSHOPPER.]

It may be well now to turn to groups presenting similar variations, not
through, but independently of, geographical distribution, and, as far as we
know, independently of conditions other than some peculiar nature and
tendency (as yet unexplained) common to members of such groups, which
nature and tendency seem to induce them to vary in certain definite lines
or directions which are different in different groups. Thus with regard to
the group of insects, of which the walking leaf is a member, Mr. Wallace
observes:[69] "The _whole family_[70] of the Phasmidae, or spectres, to
which this insect belongs, is more or less imitative, and a great number of
the species are called 'walking-stick insects,' from their singular {90}
resemblance to twigs and branches."

[Illustration: THE SIX-SHAFTED BIRD OF PARADISE.]

Again, Mr. Wallace[71] tells us of no less than four kinds of orioles,
which birds mimic, more or less, four species of a genus of honey-suckers,
the weak orioles finding their profit in being mistaken by certain birds of
prey for the strong, active, and gregarious honey-suckers. Now, many other
birds would be benefited by similar mimicry, which is none the less
confined, in this part of the world, to the oriole genus. It is true that
the absence of mimicry in other forms may be explained by their possessing
some other (as yet unobserved) means of preservation. But it is
nevertheless remarkable, not so much that one species should mimic, as that
no less than four should do so in different ways and degrees, all these{91}
four belonging to _one and the same genus_.

[Illustration: THE LONG-TAILED BIRD OF PARADISE.]

In other cases, however, there is not even the help of protective action to
account for the phenomenon. Thus we have the wonderful birds of
Paradise,[72] which agree in developing plumage unequalled in beauty, but a
beauty which, as to details, is of different kinds, and produced in
different ways in different species. To develop "beauty and singularity of
plumage" is a character of the group, but not of any one definite kind, to
be explained merely by inheritance.

{92}
[Illustration]

Again, we have the very curious horned flies,[73] which agree indeed in a
common peculiarity, but in one singularly different in detail, in different
species and not known to have any protecting effect.

Amongst plants, also, we meet with the same peculiarity. The great group of
Orchids presents a number of species which offer strange and bizarre {93}
approximations to different animal forms, and which have often the
appearance of cases of mimicry, as it were in an incipient stage.

[Illustration: HORNED FLIES.]

[Illustration: THE MAGNIFICENT BIRD OF PARADISE.]

The number of similar instances which could be brought forward from amongst
animals and plants is very great, but the examples given are, it is {94}
hoped, amply sufficient to point towards the conclusion which other facts
will, it is thought, establish, viz. that there are causes operating (in
the evocation of these harmonious diverging resemblances) other than
"Natural Selection," or heredity, and other even than merely geographical,
climatal, or any simply external conditions.

Many cases have been adduced of striking likenesses between different
animals, not due to inheritance; but this should be the less surprising, in
that the very same individual presents us with likenesses between different
parts of its body (_e.g._, between the several joints of the backbone),
which are certainly not so explicable. This, however, leads to a rather
large subject, which will be spoken of in the eighth chapter of the present
work. Here it will be enough to affirm (leaving the proof of the assertion
till later) that parts are often homologous which have no direct genetic
relationship,--a fact which harmonizes well with the other facts here
given, but which "Natural Selection," pure and simple, seems unable to
explain.

But surely the independent appearance of similar organic forms is what we
might expect, _a priori_, from the independent appearance of similar
inorganic ones. As Mr. G. H. Lewes well observes,[74] "We do not suppose
the carbonates and phosphates found in various parts of the globe--we do
not suppose that the families of alkaloids and salts have any nearer
kinship than that which consists in the similarity of their elements, and
the conditions of their combination. Hence, in organisms, as in salts,
morphological identity may be due to a community of causal connexion,
rather than community of descent.

"Mr. Darwin justly holds it to be incredible that individuals identically
the same should have been produced through Natural Selection from parents
_specifically distinct_, but he will not deny that identical forms may
issue from parents _genetically distinct_, when these parent forms and {95}
the conditions of production are identical. To deny this would be to deny
the law of causation."

Professor Huxley has, however, suggested[75] that such mineral identity may
be explained by applying also to minerals a law of descent; that is, by
considering such similar forms as the descendants of atoms which inhabited
one special part of the primitive nebular cosmos, each considerable space
of which may be supposed to have been under the influence of somewhat
different conditions.

Surely, however, there can be no real parity between the relationship of
existing minerals to nebular atoms, and the relationship of existing
animals and plants to the earliest organisms. In the first place, the
latter have produced others by generative multiplication, which mineral
atoms never did. In the second, existing animals and plants spring from the
living tissues of preceding animals and plants, while existing minerals
spring from the chemical affinity of separate elements. Carbonate of soda
is not formed, by a process of reproduction, from other carbonate of soda,
but directly by the suitable juxtaposition of carbon, oxygen, and sodium.

Instead of approximating animals and minerals in the mode suggested, it may
be that they are to be approximated in quite a contrary fashion; namely, by
attributing to mineral species an internal innate power. For, as we must
attribute to each elementary atom an innate power and tendency to form
(under the requisite external conditions) certain unions with other atoms,
so we may attribute to certain mineral species--as crystals--an innate
power and tendency to exhibit (the proper conditions being supplied) a
definite and symmetrical external form. The distinction between animals and
vegetables on the one hand, and minerals on the other, is that, while in
the organic world close similarity is the result sometimes of inheritance,
sometimes of direct production independently of parental action, in the{96}
inorganic world the latter is the constant and only mode in which such
similarity is produced.

When we come to consider the relations of species to space--in other words,
the geographical distribution of organisms--it will be necessary to return
somewhat to the subject of the independent origin of closely similar forms,
in regard to which some additional remarks will be found towards the end of
the seventh chapter.

In this third chapter an effort has been made to show that while on the
Darwinian theory concordant variations are extremely improbable, yet Nature
presents us with abundant examples of such; the most striking of which are,
perhaps, the higher organs of sense. Also that an important influence is
exercised by conditions connected with geographical distribution, but that
a deeper-seated influence is at work, which is hinted at by those special
tendencies in definite directions, which are the properties of certain
groups. Finally, that these facts, when taken together, afford strong
evidence that "Natural Selection" has not been the exclusive or predominant
cause of the various organic structural peculiarities. This conclusion has
also been re-enforced by the consideration of phenomena presented to us by
the inorganic world. [Page 97]

* * * * *

CHAPTER IV.

MINUTE AND GRADUAL MODIFICATIONS.

There are difficulties as to minute modifications, even if not
fortuitous.--Examples of sudden and considerable modifications of
different kinds.--Professor Owen's view.--Mr. Wallace.--Professor
Huxley.--Objections to sudden
changes.--Labyrinthodont.--Potto.--Cetacea.--As to origin of bird's
wing.--Tendrils of climbing plants.--Animals once supposed to be
connecting links.--Early specialization of
structure.--Macrauchenia.--Glyptodon.--Sabre-toothed
tiger.--Conclusion.

Not only are there good reasons against the acceptance of the exclusive
operation of "Natural Selection" as the one means of specific origination,
but there are difficulties in the way of accounting for such origination by
the sole action of modifications which are infinitesimal and minute,
whether fortuitous or not.

Arguments may yet be advanced in favour of the view that new species have
from time to time manifested themselves with suddenness, and by
modifications appearing at once (as great in degree as are those which
separate _Hipparion_ from _Equus_), the species remaining stable in the
intervals of such modifications: by stable being meant that their
variations only extend for a certain degree in various directions, like
oscillations in a stable equilibrium. This is the conception of Mr.
Galton,[76] who compares the development of species with a many {98}
facetted spheroid tumbling over from one facet, or stable equilibrium, to
another. The existence of internal conditions in animals corresponding with
such facets is denied by pure Darwinians, but it is contended in this work,
though not in this chapter, that something may also be said for their
existence.

The considerations brought forward in the last two chapters, namely, the
difficulties with regard to incipient and closely similar structures
respectively, together with palaeontological considerations to be noticed
later, appear to point strongly in the direction of sudden and considerable
changes. This is notably the case as regards the young oysters already
mentioned, which were taken from the shores of England and placed in the
Mediterranean, and at once altered their mode of growth and formed
prominent diverging rays, _like those of the proper Mediterranean oyster_;
as also the twenty-nine kinds of American trees, all differing from their
nearest European allies _similarly_--"leaves less toothed, buds and seeds
smaller, fewer branchlets," &c. To these may be added other facts given by
Mr. Darwin. Thus he says, "that climate, to a certain extent, directly
modifies the form of dogs."[77]

The Rev. R. Everett found that setters at Delhi, though most carefully
paired, yet had young with "nostrils more contracted, noses more pointed,
size inferior, and limbs more slender." Again, cats at Mombas, on the coast
of Africa, have short stiff hairs instead of fur, and a cat at Algoa Bay,
when left only eight weeks at Mombas, "underwent a complete metamorphosis,
having parted with its sandy-coloured fur."[78] The conditions of life seem
to produce a considerable effect on horses, and instances are given by Mr.
Darwin of pony breeds[79] having independently arisen in different parts of
the world, possessing a certain similarity in their physical {99}
conditions. Also changes due to climate may be brought about at once in a
second generation, though no appreciable modification is shown by the
first. Thus "Sir Charles Lyell mentions that some Englishmen, engaged in
conducting the operations of the Real del Monte Company in Mexico, carried
out with them some greyhounds of the best breed to hunt the hares which
abound in that country. It was found that the greyhounds could not support
the fatigues of a long chase in this attenuated atmosphere, and before they
could come up with their prey they lay down gasping for breath; but these
same animals have produced whelps, which have grown up, and are not in the
least degree incommoded by the want of density in the air, but run down the
hares with as much ease as do the fleetest of their race in this
country."[80]

We have here no action of "Natural Selection;" it was not that certain
puppies happened accidentally to be capable of enduring more rarefied air,
and so survived, but the offspring were directly modified by the action of
surrounding conditions. Neither was the change elaborated by minute
modifications in many successive generations, but appeared at once in the
second.

With regard once more to sudden alterations of form, Nathusius is said to
state positively as to pigs,[81] that the result of common experience and
of his experiments was that rich and abundant food, given during youth,
tends by some direct action to make the head broader and shorter. Curious
jaw appendages often characterize Normandy pigs, according to M. Eudes
Deslongchamps. Richardson figures these appendages on the old "Irish
greyhound pig," and they are said by Nathusius to appear occasionally in
all the long-eared races. Mr. Darwin observes,[82] "As no wild pigs are
known to have analogous appendages, we have at present no reason to {100}
suppose that their appearance is due to reversion; and if this be so, we
are forced to admit that somewhat complex, though apparently useless
structures may be suddenly developed without the aid of selection." Again,
"Climate directly affects the thickness of the skin and hair" of
cattle.[83] In the English climate an individual Porto Santo rabbit[84]
recovered the proper colour of its fur in rather less than four years. The
effect of the climate of India on the turkey is considerable. Mr. Blyth[85]
describes it as being much degenerated in size, "utterly incapable of
rising on the wing," of a black colour, and "with long pendulous appendages
over the beak enormously developed." Mr. Darwin again tells us that there
has suddenly appeared in a bed of common broccoli a peculiar variety,
faithfully transmitting its newly acquired and remarkable characters;[86]
also that there have been a rapid transformation and transplantation of
American varieties of maize with a European variety;[87] that certainly
"the Ancon and Manchamp breeds of sheep," and that (all but certainly)
Niata cattle, turnspit and pug dogs, jumper and frizzled fowls, short-faced
tumbler pigeons, hook-billed ducks, &c., and a multitude of vegetable
varieties, have suddenly appeared in nearly the same state as we now see
them.[88] Lastly, Mr. Darwin tells us, that there has been an occasional
development (in five distinct cases) in England of the "japanned" or
"black-shouldered peacock" (_Pavo nigripennis_), a distinct species,
according to Dr. Sclater,[89] yet arising in Sir J. Trevelyan's flock
composed entirely of the common kind, and increasing, "_to the extinction
of the previously existing breed_."[90] Mr. Darwin's only explanation of
the phenomena (on the supposition of the species being distinct) is by{101}
reversion, owing to a supposed ancestral cross. But he candidly admits, "I
have heard of no other such case in the animal or vegetable kingdom." On
the supposition of its being only a variety, he observes, "The case is the
most remarkable ever recorded of the abrupt appearance of a new form, which
so closely resembles a true species, that it has deceived one of the most
experienced of living ornithologists."

As to plants, M. C. Naudin[91] has given the following instances of the
sudden origination of apparently permanent forms. "The first case mentioned
is that of a poppy, which took on a remarkable variation in its fruit--a
crown of secondary capsules being added to the normal central capsule. A
field of such poppies was grown, and M. Goeppert, with seed from this field,
obtained still this monstrous form in great quantity. Deformities of ferns
are sometimes sought after by fern-growers. They are now always obtained by
taking spores from the abnormal parts of the monstrous fern; from which
spores ferns presenting the same peculiarities invariably grow.... The most
remarkable case is that observed by Dr. Godron, of Nancy. In 1861 that
botanist observed, amongst a sowing of _Datura tatula_, the fruits of which
are very spinous, a single individual of which the capsule was perfectly
smooth. The seeds taken from this plant all furnished plants having the
character of this individual. The fifth and sixth generations are now
growing without exhibiting the least tendency to revert to the spinous
form. More remarkable still, when crossed with the normal _Datura tatula_,
hybrids were produced, which, in the second generation, reverted to the
original types, as true hybrids do."

There are, then, abundant instances to prove that considerable {102}
modifications may suddenly develop themselves, either due to external
conditions or to obscure internal causes in the organisms which exhibit
them. Moreover, these modifications, from whatever cause arising, are
capable of reproduction--the modified individuals "breeding true."

The question is whether new species have been developed by non-fortuitous
variations which are insignificant and minute, or whether such variations
have been comparatively sudden, and of appreciable size and importance?
Either hypothesis will suit the views here maintained equally well (those
views being opposed only to fortuitous, indefinite variations), but the
latter is the more remote from the Darwinian conception, and yet has much
to be said in its favour.

Professor Owen considers, with regard to specific origination, that natural
history "teaches that the change would be sudden and considerable: it
opposes the idea that species are transmitted by minute and slow
degrees."[92] "An innate tendency to deviate from parental type, operating
through periods of adequate duration," being "the most probable nature, or
way of operation of the secondary law, whereby species have been derived
one from the other."[93]

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