The Project Gutenberg ebook of Darwinism (1889), by Alfred Russel Wallace

toes, which would accordingly diminish in size, till, after a long

series of changes, the records of which are so well preserved in the

American tertiary rocks, the true one-toed horse was developed. In soft

or swampy ground, on the other hand, the tendency would be to spread out

the foot so that there were two toes on each side. The two middle toes

would thus be most used and most subject to strains, and would,

therefore, increase at the expense of the lateral toes. There would be,

no doubt, an advantage in these two functional toes being of equal size,

so as to prevent twisting of the foot while walking; and variations

tending to bring this about would be advantageous, and would therefore

be preserved. Thus, by a parallel series of changes in another

direction, adapted to a distinct set of conditions, we should arrive at

the symmetrical divided hoofs of our deer and cattle. The fact that

sheep and goats are specially mountain and rock-loving animals may be

explained by their being a later modification, since the divided hoof

once formed is evidently well adapted to secure a firm footing on rugged

and precipitous ground, although it could hardly have been first

developed in such localities. Mr. Cope thus concludes: "Certain it is

that the length of the bones in the feet of the ungulate orders has a

direct relation to the dryness of the ground they inhabit, and the

possibility of speed which their habit permits them or necessarily

imposes on them."[205]
If there is any truth in the explanation here briefly summarised, it

must entirely depend on the fact of individual modifications thus

produced being hereditary, and we yet await the proof of this. In the

meantime it is clear that the very same results could have been brought

about by variation and natural selection. For the toes, like all other

organs, vary in size and proportions, and in their degree of union or

separation; and if in one group of animals it was beneficial to have the

middle toe larger and longer, and in another set to have the two middle

toes of the same size, nothing can be more certain than that these

particular modifications would be continuously preserved, and the very

results we see ultimately produced.
The oft-repeated objections that the cause of variations is unknown,

that there must be something to determine variations in the right

direction; that "natural selection includes no actively progressive

principle, but must wait for the development of variation, and then,

after securing the survival of the best, wait again for the best to

project its own variations for selection," we have already sufficiently

answered by showing that variation--in abundant or typical species--is

always present in ample amount; that it exists in all parts and organs;

that these vary, for the most part, independently, so that any required

combination of variations can be secured; and finally, that all

variation is necessarily either in excess or defect of the mean

condition, and that, consequently, the right or favourable variations

are so frequently present that the unerring power of natural selection

never wants materials to work upon.

"Intelligence is a conservative principle, and will always direct effort

and use into lines which will be beneficial to its possessor. Here we

have the source of the fittest, _i.e._ addition of parts by increase and

location of growth-force, directed by the influence of various kinds of

compulsion in the lower, and intelligent option among higher animals.

Thus intelligent choice, taking advantage of the successive evolution of

physical conditions, may be regarded as the _originator of the fittest_,

while natural selection is the tribunal to which all results of

accelerated growth are submitted. This preserves or destroys them, and

determines the new points of departure on which accelerated growth shall

build."[206]

itself--determining its own variation, is so evidently a very partial

theory, inapplicable to the whole vegetable kingdom, and almost so to

all the lower forms of animals, amongst which, nevertheless, there is

the very same adaptation and co-ordination of parts and functions as

among the highest, that it is strange to see it put forward with such

confidence as necessary for the completion of Darwin's theory. If "the

various kinds of compulsion"--by which are apparently meant the laws of

variation, growth, and reproduction, the struggle for existence, and the

actions necessary to preserve life under the conditions of the animal's

environment--are sufficient to have developed the varied forms of the

lower animals and of plants, we can see no reason why the same

"compulsion" should not have carried on the development of the higher

animals also. The action of this "intelligent option" is altogether

unproved; while the acknowledgment that natural selection is the

tribunal which either preserves or destroys the variations submitted to

it, seems quite inconsistent with the statement that intelligent choice

is the "orginator of the fittest," since whatever is really "the

fittest" can never be destroyed by natural selection, which is but

another name for the survival of the fittest. If "the fittest" is always

definitely produced by some other power, then natural selection is not

wanted. If, on the other hand, both fit and unfit are produced, and

natural selection decides between them, that is pure Darwinism, and Mr.

Cope's theories have added nothing to it.

Milhausenii; 1, tail-lobe of A. salina, and its transition through

2,3,4,5, to 6, into that of A. Milhausenii; 7, post-abdomen of A.

salina; 8, post-abdomen of a form bred in brackish water; 9, gill of A.

Milhausenii; 10, gill of A. salina. (From Schmankewitsch.)]

_Semper on the Direct Influence of the Environment._

adopts the view of the direct transforming power of the environment, and

has brought together an immense body of interesting facts showing the

influence of food, of light, of temperature, of still water and moving

water, of the atmosphere and its currents, of gravitation, and of other

organisms, in modifying the forms and other characteristics of

animals.[207] He believes that these various influences produce a direct

and important effect, and that this effect is accumulated by

inheritance; yet he acknowledges that we have no direct evidence of

this, and there is hardly a single case adduced in the book which is not

equally well explained by adaptation, brought about by the survival of

beneficial variations. Perhaps the most remarkable case he has brought

forward is that of the transformation of species of crustaceans by a

change in the saltness of the water (see Fig. 35). Artemia salina lives

in brackish water, while A. Milhausenii inhabits water which is much

salter. They differ greatly in the form of the tail-lobes, and in the

presence or absence of spines upon the tail, and had always been

considered perfectly distinct species. Yet either was transformed into

the other in a few generations, during which the saltness of the water

was gradually altered. Yet more, A. salina was gradually accustomed to

fresher water, and in the course of a few generations, when the water

had become perfectly fresh, the species was changed into Branchipus

stagnalis, which had always been considered to belong to a different

genus on account of differences in the form of the antennae and of the

posterior segments of the body (see Fig. 36). This certainly appears to

be a proof of change of conditions producing a change of form

independently of selection, and of that change of form, while remaining

under the same conditions, being inherited. Yet there is this

peculiarity in the case, that there is a chemical change in the water,

and that this water permeates the whole body, and must be absorbed by

the tissues, and thus affect the ova and even the reproductive

elements, and in this way may profoundly modify the whole organisation.

Why and how the external effects are limited to special details of the

structure we do not know; but it does not seem as if any far-reaching

conclusions as to the cumulative effect of external conditions on the

higher terrestrial animals and plants, can be drawn from such an

exceptional phenomenon. It seems rather analogous to those effects of

external influences on the very lowest organisms in which the vegetative

and reproductive organs are hardly differentiated, in which case such

effects are doubtless inherited.[208]

_Professor Geddes's Theory of Variation in Plants._

Patrick Geddes laid down the outlines of a fundamental theory of plant

variation, which he has further extended in the article "Variation and

Selection" in the _Encydopaedia Britannica_, and in a paper read before

the Linnaean Society but not yet published.
A theory of variation should deal alike with the origin of specific

distinctions and with those vaster differences which characterise the

larger groups, and he thinks it should answer such questions as--How an

axis comes to be arrested to form a flower? how the various forms of

inflorescence were evolved? how did perigynous or epigynous flowers

arise from hypogynous flowers? and many others equally fundamental.

Natural selection acting upon numerous accidental variations will not,

he urges, account for such general facts as these, which must depend on

some constant law of variation. This law he believes to be the

well-known antagonism of vegetative and reproductive growth acting

throughout the whole course of plant development; and he uses it to

explain many of the most characteristic features of the structure of

flowers and fruits.
Commencing with the origin of the flower, which all botanists agree in

regarding as a shortened branch, he explains this shortening as an

inevitable physiological fact, since the cost of the development of the

reproductive elements is so great as necessarily to check vegetative

growth. In the same manner the shortening of the inflorescence from

raceme to spike or umbel, and thence to the capitulum or dense

flower-head of the composite plants is brought about. This shortening,

carried still further, produces the flattened leaf-like receptacle of

Dorstenia, and further still the deeply hollowed fruity receptacle of

the fig.
The flower itself undergoes a parallel modification due to a similar

cause. It is formed by a series of modified leaves arranged round a

shortened axis. In its earlier stages the number of these modified

leaves is indefinite, as in many Ranunculaceae; and the axis itself is

not greatly shortened, as in Myosurus. The first advance is to a

definite number of parts and a permanently shortened axis, in the

arrangement termed hypogynous, in which all the whorls are quite

distinct from each other. In the next stage there is a further

shortening of the central axis, leaving the outer portion as a ring on

which the petals are inserted, producing the arrangement termed

perigynous. A still further advance is made by the contraction of the

axis, so as to leave the central part forming the ovary quite below the

flower, which is then termed epigynous.

be determined by the continuous checking of vegetation by reproduction

along what is an absolute groove of progressive change. This being the

case, the importance of natural selection is greatly diminished. Instead

of selecting and accumulating spontaneous indefinite variations, its

function is to retard them after the stage of maximum utility has been

independently reached. The same simple conception is said to unlock

innumerable problems of vegetable morphology, large and small alike. It

explains the inevitable development of gymnosperm into angiosperm by the

checked vegetative growth of the ovule-bearing leaf or carpel; while

such minor adaptations as the splitting fruit of the geranium or the

cupped stigma of the pansy, can be no longer looked upon as achievements

of natural selection, but must be regarded as naturally traceable to

the vegetative checking of their respective types of leaf organ. Again,

a detailed examination of spiny plants practically excludes the

hypothesis of mammalian selection altogether, and shows spines to arise

as an expression of the diminishing vegetativeness--in fact, the ebbing

vitality of a species.[209]

_Objections to the Theory._
The theory here sketched out is enticing, and at first sight seems

calculated to throw much light on the history of plant development; but

on further consideration, it seems wanting in definiteness, while it is

beset with difficulties at every step. Take first the shortening of the

raceme into the umbel and the capitulum, said to be caused by arrest of

vegetative growth, due to the antagonism of reproduction. If this were

the whole explanation of the phenomenon, we should expect the quantity

of seed to increase as this vegetative growth diminished, since the seed

is the product of the reproductive energy of the plant, and its quantity

the best measure of that energy. But is this the case? The ranunculus

has comparatively few seeds, and the flowers are not numerous; while in

the same order the larkspur and the columbine have far more seeds as

well as more flowers, but there is no shortening of the raceme or

diminution of the foliage, although the flowers are large and complex.

So, the extremely shortened and compressed flower-heads of the

compositae produce comparatively few seeds--one only to each flower;

while the foxglove, with its long spike of showy flowers, produces an

enormous number.

hypogynous, perigynous, and epigynous flowers were an indication of

preponderant reproduction and diminished vegetation, we should find

everywhere some clear indications of this fact. The plants with

hypogynous flowers should, as a rule, have less seed and more vigorous

and abundant foliage than those at the other extreme with epigynous

flowers. But the hypogynous poppies, pinks, and St. John's worts have

abundance of seed and rather scanty foliage; while the epigynous

dogwoods and honeysuckles have few seeds and abundant foliage. If,

instead of the number of the seeds, we take the size of the fruit as an

indication of reproductive energy, we find this at a maximum in the

gourd family, yet their rapid and luxuriant growth shows no diminution

of vegetative power. So that the statement that plant modifications

proceed "along an absolute groove of progressive change" is contradicted

by innumerable facts indicating advance and regression, improvement or

degradation, according as the ever-changing environment renders one form

more advantageous than the other. As one instance I may mention the

Anonaceae or custard-apple tribe, which are certainly an advance from

the Ranunculaceae; yet in the genus Polyalthea the fruit consists of a

number of separate carpels, each borne on a long stalk, as if reverting

to the primitive stalked carpellary leaves.

_On the Origin of Spines._

which considers spines to be an indication of the "ebbing vitality of a

species," and which excludes "mammalian selection altogether." If this

were true, spines should occur mainly in feeble, rare, and dying-out

species, instead of which we have the hawthorn, one of our most vigorous

shrubs or trees, with abundant vitality and an extensive range over the

whole Palaearctic region, showing that it is really a dominant species.

In North America the numerous thorny species of Crataegus are equally

vigorous, as are the false acacia (Robinia) and the honey-locust

(Gleditschia). Neither have the numerous species of very spiny Acacias

been noticed to be rarer or less vigorous than the unarmed kinds.
On the other point--that spines are not due to mammalian selection--we

are able to adduce what must be considered direct and conclusive

evidence. For if spines, admittedly produced by aborted branches,

petioles, or peduncles, are due solely or mainly to diminished

vegetativeness or ebbing vitality, they ought to occur in all countries

alike, or at all events in all whose similar conditions tend to check

vegetation; whereas, if they are, solely or mainly, developed as a

protection against the attacks of herbivorous mammals, they ought to be

most abundant where these are plentiful, and rare or absent where

indigenous mammalia are wanting. Oceanic islands, as compared with

continents, would thus furnish a crucial test of the two theories; and

Mr. Hemsley of Kew, who has specially studied insular floras, has given

me some valuable information on this point. He says: "There are no spiny

or prickly plants in the indigenous element of the St. Helena flora. The

relatively rich flora of the Sandwich Isles is not absolutely without a

prickly plant, but almost so. All the endemic genera are unarmed, and

the endemic species of almost every other genus. Even such genera as

Zanthoxylon, Acacia, Xylosoma, Lycium, and Solanum, of which there are

many armed species in other countries, are only represented by unarmed

species. The two endemic Rubi have the prickles reduced to the setaceous

condition, and the two palms are unarmed.
"The flora of the Galapagos includes a number of prickly plants, among

them several cacti (these have not been investigated and may be American

species), but I do not think one of the known endemic species of any

family is prickly or spiny.

the formidably armed species of wild Spaniard (Aciphylla), one species

of Rubus, the pungent-leaved Epacrideae and a few others."
Mr. J.G. Baker of Kew, who has specially studied the flora of Mauritius

and the adjacent islands, also writes me on this point. He says: "Taking

Mauritius alone, I do not call to mind a single species that is a

spinose endemic tree or shrub. If you take the whole group of islands

(Mauritius, Bourbon, Seychelles, and Rodriguez), there will be about a

dozen species, but then nine of these are palms. Leaving out palms, the

trees and shrubs of that part of the world are exceptionally

non-spinose."

theory of spines being caused solely by checked vegetative growth, due

to weakness of constitution or to an arid soil and climate. For the

Galapagos and many parts of the Sandwich Islands are very arid, as is a

considerable part of the North Island of New Zealand. Yet in our own

moist climate and with our very limited number of trees and shrubs we

have about eighteen spiny or prickly species, more, apparently, than in

the whole endemic floras of the Mauritius, Sandwich Islands, and

Galapagos, though these are all especially rich in shrubby and arboreal

species. In New Zealand the prickly Rubus is a leafless trailing plant,

and its prickles are probably a protection against the large snails of

the country, several of which have shells from two to three and a half

inches long.[210] The "wild Spaniards" are very spiny herbaceous

Umbelliferae, and may have gained their spines to preserve them from

being trodden down or eaten by the Moas, which, for countless ages, took

the place of mammals in New Zealand. The exact use or meaning of the

spines in palms is more doubtful, though they are, no doubt, protective

against some animals; but it is certainly an extraordinary fact that in

the entire flora of the Mauritius, so largely consisting of trees and

shrubs, not a single endemic species should be thorny or spiny.

proportion of spiny and thorny species, and that these rise to a maximum

in South Africa, where herbivorous mammalia were (before the settlement

of the country), perhaps, more abundant and varied than in any other

part of the world; while another district, remarkable for well-armed

vegetation, is Chile, where the camel-like vicugnas, llamas, and

alpacas, and an abundance of large rodents wage perpetual war against

shrubby vegetation, we shall see the full significance of the almost

total absence of thorny and spiny plants in the chief oceanic islands;

and so far from "excluding the hypothesis of mammalian selection

altogether," we shall find in this hypothesis the only satisfactory

explanation of the facts.

conclude that, although the antagonism between vegetative and

reproductive growth is a real agency, and must be taken account of in

our endeavour to explain many of the fundamental facts in the structure

and form of plants, yet it is so overpowered and directed at every step

by the natural selection of favourable variations, that the results of

its exclusive and unmodified action are nowhere to be found in nature.

It may be allowed to rank as one of those "laws of growth," of which so

many have now been indicated, and which were always recognised by Darwin

as underlying all variation; but unless we bear in mind that its action

must always be subordinated to natural selection, and that it is

continually checked, or diverted, or even reversed by the necessity of

adaptation to the environment, we shall be liable to fall into such

glaring errors as the imputing to "ebbing vitality" alone such a

widespread phenomenon as the occurrence of spines and thorns, while

ignoring altogether the influence of the organic environment in their

production.[211]
The sketch now given of the chief attempts that have been made to prove

that either the direct action of the environment or certain fundamental