* * * * *

Horns wherever they occur, are found to be of high importance for

purposes of classification. They are restricted to the Ruminants, and

appear under three different forms or types--namely solid, as in

antelopes; hollow, as in sheep; and deciduous, as in deer. Now, in each

of these divisions we have a tolerably complete palaeontological history

of the evolution of horns. The early ruminants were altogether hornless

(Fig. 60). Then, in the middle Miocene, the first antelopes appeared

with tiny horns, which progressively increased in size among the

ever-multiplying species of antelopes until the present day. But it is

in the deer tribe that we meet with even better evidence touching the

progressive evolution of horns; because here not only size, but shape,

is concerned. For deer's horns, or antlers, are arborescent; and hence

in their case we have an opportunity of reading the history, not only of

a progressive growth in size, but also of an increasing development of

form. Among the older members of the tribe, in the lower Miocene, there

are no horns at all. In the mid-Miocene we meet with two-pronged horns

(_Cervus dicrocerus_, Figs. 61, 62, 1/5 nat. size). Next, in the upper

Miocene (_C. matheronis_, Fig. 63, 1/8 nat. size), and extending into

the Pliocene (_C. pardinensis_, Fig. 64, 1/18 nat. size), we meet with

three-pronged horns. Then, in the Pliocene we find also four-pronged

horns (_C. issiodorensis_, Fig. 65, 1/16 nat. size), leading us to

five-pronged (_C. tetraceros_). Lastly, in the Forest-bed of Norfolk we

meet with arborescent horns (_C. Sedgwickii_, Fig. 66, 1/35 nat. size).

The life-history of existing stags furnishes a parallel development

(Fig. 67), beginning with a single horn (which has not yet been found

palaeontologically), going on to two prongs, three prongs, four prongs,

and afterwards branching.

[Illustration: FIG. 60.--Skull of _Oreodon Culbertsoni_. (After

Leidy.)]

[Illustration: FIGS. 61-66. The series is reduced from Gaudry's

illustrations, after Farge, Croizet, Jobert and Boyd Dawkins.]

[Illustration: FIG. 67.--Successive stages in the development of an

existing Deer's Antlers. (After Gaudry, but a better illustration

has already been given on p. 100.)]

* * * * *

Coming now to bones, we have a singularly complete record of transition

from one type or pattern of structure to another in the phylogenetic

history of tails. This has been so clearly and so tersely conveyed by

Prof. Le Conte, that I cannot do better than quote his statement.

It has long been noticed that there are among fishes two styles of

tail-fins. These are the even-lobed, or homocercal (Fig. 68), and

the uneven-lobed, or heterocercal (Fig. 69). The one is

characteristic of ordinary fishes (teleosts), the other of sharks

and some other orders. In structure the difference is even more

fundamental than in form. In the former style the backbone stops

abruptly in a series of short, enlarged joints, and thence sends

off rays to form the tail-fin (Fig. 68); in the latter the

backbone runs through the fin to its very point, growing slenderer

by degrees, and giving off rays above and below from each joint,

but the rays on the lower side are much longer (Fig. 69). This type

of fin is, therefore, _vertebrated_, the other _non-vertebrated_.

Figs. 68 and 69 show these two types in form and structure. But

there is still another type found only in the lowest and most

generalized forms of fishes. In these the tail-fin is vertebrated

and yet symmetrical. This type is shown in Fig. 70.

[Illustration: FIG. 68.--Homocercal Tail, showing (A) external form

and (B) internal structure.]

[Illustration: FIG. 69.--Heterocercal Tail, showing (A) external

form and (B) internal structure.]

[Illustration: FIG. 70.--Vertebrated but symmetrical fin

(diphycercal), showing (A) external form and (B) internal

structure.]

Now, in the development of a teleost fish (Fig. 68), as has been

shown by Alexander Agassiz, the tail-fin is first like Fig. 70;

then becomes heterocercal, like Fig. 69; and, finally, becomes

homocercal like Fig. 68. Why so? Not because there is any special

advantage in this succession of forms; for the changes take place

either in the egg or else in very early embryonic states. The

answer is found in the fact that _this is the order of change in

the phylogenetic series_. The earliest fish-tails were either like

Fig. 69 or Fig. 70; never like Fig. 68. The earliest of all were

almost certainly like Fig. 70; then they became like Fig. 69; and,

finally, only much later in geological history (Jurassic or

Cretaceous), they became like Fig. 68. This order of change is

still retained in the embryonic development of the last introduced

and most specialized order of existing fishes. The family history

is repeated in the individual history.

Similar changes have taken place in the form and structure of

birds' tails. The earliest bird known--the Jurassic

_Archaeopteryx_--had a long reptilian tail of twenty-one joints,

each joint bearing a feather on each side, right and left (Fig.

71): [see also Fig. 73]. In the typical modern bird, on the

contrary, the tail-joints are diminished in number, shortened up,

and enlarged, and give out long feathers, fan-like, to form the

so-called tail (Fig. 72). The _Archaeopteryx'_ tail is

_vertebrated_, the typical bird's _non-vertebrated_. This

shortening up of the tail did not take place at once, but

gradually. The Cretaceous birds, intermediate in time, had tails

intermediate in structure. The _Hesperornis_ of Marsh had twelve

joints. At first--in Jurassic strata--the tail is fully a half of

the whole vertebral column. It then gradually shortens up until it

becomes the aborted organ of typical modern birds. Now, in

embryonic development, the tail of the modern typical bird _passes

through all these stages_. At first the tail is nearly one half the

whole vertebral column; then, as development goes on, while the

rest of the body grows, the growth of the tail stops, and thus

finally becomes the aborted organ we now find. The ontogeny still

passes through the stages of the phylogeny. The same is true of all

tailless animals.

[Illustration: FIG. 71.--Tail of _Archaeopteryx_. A indicates origin

of simply-jointed tail.]

[Illustration: FIG. 72.--Tail of modern Bird. The numerals indicate

the foreshortened, enlarged, and consolidated joints; _f_, terminal

segment of the vertebral column; D, shafts of feathers.]

[Illustration: FIG. 73.--_Archaeopteryx macura_, restored, 1/2 nat.

size. (After Flower.) The section of the tail is copied from Owen,

nat. size.]

The extinct _Archaeopteryx_ above alluded to presents throughout its

whole organization a most interesting assemblage of "generalized

characters." For example, its teeth, and its still unreduced digits of

the wings (which, like those of the feet, are covered with scales),

refer us, with almost as much force as does the vertebrated tail, to the

Sauropsidian type--or the trunk from which birds and reptiles have

diverged.

We will next consider the palaeontological evidence which we now

possess of the evolution of mammalian limbs, with special reference to

the hoofed animals, where this line of evidence happens to be most

complete.

I may best begin by describing the bones as these occur in the sundry

branches of the mammalian type now living. As we shall presently see,

the modifications which the limbs have undergone in these sundry

branches chiefly consist in the suppression of some parts and the

exaggerated development of others. But, by comparing all mammalian limbs

together, it is easy to obtain a generalized type of mammalian limb,

which in actual life is perhaps most nearly conformed to in the case of

bears. I will therefore choose the bear for the purpose of briefly

expounding the bones of mammalian limbs in general--merely asking it to

be understood, that although in the case of many other mammalia some of

these bones may be dwindled or altogether absent, while others may be

greatly exaggerated as to relative size, in no case do any _additional_

bones appear.

On looking, then, at the skeleton of a bear (Fig. 74), the first thing

to observe is that there is a perfect serial homology between the bones

of the hind legs and of the fore legs. The thigh-bone, or femur,

corresponds to the shoulder-bone, or humerus; the two shank bones (tibia

and fibula) correspond to the two arm-bones (radius and ulna); the many

little ankle-bones (tarsals) correspond to the many little wrist-bones

(carpals); the foot-bones (meta-tarsals) correspond to the hand-bones

(meta-carpals); and, lastly, the bones of each of the toes correspond to

those of each of the fingers.

[Illustration: FIG. 74.--Skeleton of Polar Bear, drawn from nature

(_Brit. Mus._).]

The next thing to observe is, that the disposition of bones in the case

of the bear is such that the animal walks in the way that has been

called plantigrade. That is to say, all the bones of the fingers, as

well as those of the toes, feet, and ankles, rest upon the ground, or

help to constitute the "soles." Our own feet are constructed on a

closely similar pattern. But in the majority of living mammalian forms

this is not the case. For the majority of mammals are what has been

called digitigrade. That is to say, the bones of the limb are so

disposed that both the foot and hand bones, and therefore also the ankle

and wrist, are removed from the ground altogether, so that the animal

walks exclusively upon its toes and fingers--as in the case of this

skeleton (Fig. 75), which is the skeleton of a lion. The next figures

display a series of limbs, showing the progressive passage of a

completely plantigrade into a highly digitigrade type--the curved lines

of connexion serving to indicate the homologous bones (Figs. 76, 77).

[Illustration: _Fig_. 75.--Skeleton of Lion. (After Huxley.)]

[Illustration: FIG. 76.--Anterior limb of Man, Dog, Hog, Sheep, and

Horse. (After Le Conte.) _Sc_, shoulder-blade; _c_, coracoid; _a_,

_b_, bones of fore-arm; 5, bones of the wrist; 6, bones of the hand;

7, bones of the fingers.]

[Illustration: FIG. 77.--Posterior limb of Man, Monkey, Dog, Sheep

and Horse. (After Le Conte.) 1, Hip-joint; 2, thigh-bone; 3,

knee-joint; 4, bones of leg; 5, ankle-joint; 6, bones of foot; 7,

bones of toes.]

I will now proceed to detail the history of mammalian limbs, as this has

been recorded for us in fossil remains.

The most generalized or primitive types of limb hitherto discovered in

any vertebrated animal above the class of fishes, are those which are

met with in some of the extinct aquatic reptiles. Here, for instance, is

a diagram of the left hind limb of _Baptanodon discus_ (Fig. 78). It has

six rows of little symmetrical bones springing from a leg-like origin.

But the whole structure resembles the fin of a fish about as nearly as

it does the leg of a mammal. For not only are there six rows of bones,

instead of five, suggestive of the numerous rays which characterise the

fin of a fish; but the structure as a whole, having been covered over

with blubber and skin, was throughout flexible and unjointed--thus in

function, even more than in structure, resembling a fin. In this

respect, also, it must have resembled the paddle of a whale (see Fig.

79); but of course the great difference will be noted, that the paddle

of a whale reveals the dwindled though still clearly typical bones of a

true mammalian limb; so that although in outward form and function these

two paddles are alike, their inward structure clearly shows that while

the one testifies to the absence of evolution, the other testifies to

the presence of degeneration. If the paddle of _Baptanodon_ had occurred

in a whale, or the paddle of a whale had occurred in _Baptanodon_,

either fact would in itself have been well-nigh destructive of the whole

theory of evolution.

[Illustration: FIG. 78.--A, posterior limb of _Baptanodon discus_.

(After Marsh.) F, thigh-bone; I to VI, undifferentiated bones of the

leg and foot. B, anterior limb of _Chelydra serpentina_. (After

Gegenbaur.) U and R, bones of the fore-arm; I to V, fully

differentiated bones of the hand, following those of the wrist.]

[Illustration: FIG. 79.--Paddle of a Whale.]

Such, then, is the most generalized as it is the most ancient type of

vertebrate limb above the class of fishes. Obviously it is a type

suited only to aquatic life. Consequently, when aquatic Vertebrata began

to become terrestrial, the type would have needed modification in order

to serve for terrestrial locomotion. In particular, it would have needed

to gain in consolidation and in firmness, which means that it would have

needed also to become jointed. Accordingly, we find that this archaic

type gave place in land-reptiles to the exigencies of these

requirements. Here for example is a diagram, copied from Gegenbaur, of

the right fore-foot of _Chelydra serpentina_ (Fig. 78). As compared with

the homologous limb of its purely aquatic predecessor, there is to be

noticed the disappearance of one of the six rows of small bones, a

confluence of some of the remainder in the other five rows, a

duplication of the arm-bone into a radius and ulna, in order to admit of

jointed rotation of the hand, and a general disposition of the small

bones below these arm-bones, which clearly foreshadows the joint of the

wrist. Indeed, in this fore-foot of _Chelydra_, a child could trace all

the principal homologies of the mammalian counterpart, growing, like the

next stage in a dissolving view, out of the primitive paddle of

_Baptanodon_--namely, first the radius and ulna, next the carpals, then

the meta-carpals, and, lastly, the three phalanges in each of the five

digits.

Such a type of foot no doubt admirably meets the requirements of slow

reptilian locomotion over swampy ground. But for anything like rapid

locomotion over hard and uneven ground, greater modifications would be

needed. Such modifications, however, need not be other in kind: it is

enough that they should continue in the same line of advance, so as to

reach a higher degree of firmness, combined with better joints.

Accordingly we find that this took place, not indeed among reptiles,

whose habits of cold-blooded life have not changed, but among their

warm-blooded descendants, the mammals. Moreover, when we examine the

whole mammalian series, we find that the required modifications must

have taken place in slightly different ways in three lines of descent

simultaneously. We have first the plantigrade and digitigrade

modifications already mentioned (pp. 178, 179) Of these the plantigrade

walking entailed least change, because most resembling the ancestral or

lizard-like mode of progression. All that was here needed was a general

improvement as to relative lengths of bones, with greater consolidation

and greater flexibility of joints. Therefore I need not say anything

more about the plantigrade division. But the digitigrade modification

necessitated a change of structural plan, to the extent of raising the

wrist and ankle joints off the ground, so as to make the quadruped walk

on its fingers and toes. We meet with an interesting case of this

transition in the existing hare, which while at rest supports itself on

the whole hind foot after the manner of a plantigrade animal, but when

running does so upon the ends of its toes, after the manner of a

digitigrade animal.

It is of importance for us to note that this transition from the

original plantigrade to the more recent digitigrade type, has been

carried out on two slightly different plans in two different lines of

mammalian descent. The hoofed mammals--which are all digitigrade--are

sub-classified as artiodactyls and perissodactyls, i. e. even-toed and

odd-toed. Now, whether an animal has an even or an odd number of toes

may seem a curiously artificial distinction on which to found so

important a classification of the mammalian group. But if we look at the

matter from a less empirical and more intelligent point of view, we

shall see that the alternative of having an even or an odd number of

toes carries with it alternative consequences of a practically important

kind to any animal of the digitigrade type. For suppose an aboriginal

five-toed animal, walking on the ends of its five toes, to be called

upon to resign some of his toes. If he is left with an even number, it

must be two or four; and in either case the animal would gain the

firmest support by so disposing his toes as to admit of the axis of his

foot passing between an equal number of them--whether it be one or two

toes on each side. On the other hand, if our early mammal were called

upon to retain an odd number of toes, he would gain best support by

adjusting matters so that the axis of his foot should be coincident with

his middle toe, whether this were his only toe, or whether he had one on

either side of it. This consideration shows that the classification into

even-toed and odd-toed is not so artificial as it no doubt at first

sight appears. Let us, then, consider the stages in the evolution of

both these types of feet.

Going back to the reptile _Chelydra_, it will be observed that the axis

of the foot passes down the middle toe, which is therefore supported by

two toes on either side (Fig. 78). It may also be noticed that the wrist

or ankle bones do not interlock, either with one another or with the

bones of the hand or foot below them. This, of course, would give a

weak foot, suited to slow progression over marshy ground--which, as we

have seen, was no doubt the origin of the mammalian plantigrade foot.

Here, for instance, to all intents and purposes, is a similar type of

foot, which belonged to a very early mammal, antecedent to the elephant

series, the horse series, the rhinoceros, the hog, and, in short, all

the known hoofed mammalia (Fig. 80). It was presumably an inhabitant of

swampy ground, slow in its movements, and low in its intelligence.

[Illustration: FIG. 80.--Fossil skeleton of _Phenacodus primavus_.

(After Cope.)]

But now, as we have seen, for more rapid progression on hard uneven

ground, a stronger and better jointed foot would be needed. Therefore we

find the bones of the wrist and ankle beginning to interlock, both among

themselves and also with those of the foot and hand immediately below

them. Such a stage of evolution is still apparent in the now existing

elephant. (See Fig. 81.)

[Illustration: FIG. 81.--Bones of the foot of four different forms

of the perissodactyl type, showing gradual reduction in the number

of digits, coupled with a greater consolidation of the bones above

the digits. The series reads from right to left. Drawn from nature

(_Brit. Mus._).]

Next, however, a still stronger foot was made by the still further

interlocking of the wrist and ankle bones, so that both the first and

second rows of them were thus fitted into each other, as well as into

the bones of the hand and foot beneath. This further modification is

clearly traceable in some of the earlier perissodactyls, and occurs in

the majority at the present time. Compare, for example, the greater

interlocking and consolidation of these small bones in the Rhinoceros as

contrasted with the Elephant (Fig. 81). Moreover, simultaneously with

these consolidating improvements in the mechanism of the wrist and ankle

joints, or possibly at a somewhat later period, a reduction in the

number of digits began to take place. This was a continuation of the

policy of consolidating the foot, analogous to the dropping out of the

sixth row of small bones in the paddle of _Baptanodon_. (Fig. 78.) In

the pentadactyl plantigrade foot of the early mammals, the first digit,

being the shortest, was the first to leave the ground, to dwindle,

and finally to disappear. More work being thus thrown on the remaining

four, they were strengthened by interlocking with the wrist (or ankle)

bones above them, as just mentioned; and also by being brought closer

together.

[Illustration: FIG. 82.--Bones of the foot of four different forms

of the artiodactyl type, showing gradual reduction of the number of

digits, coupled with a greater consolidation of the bones above the

digits. The series reads from right to left. Drawn from nature

(_Brit. Mus._).]

The changes which followed I will render in the words of Professor

Marsh.

Two kinds of reduction began. One leading to the existing

perissodactyl foot, and the other, apparently later, resulting in

the artiodactyl type. In the former the axis of the foot remained

in the middle of the third digit, as in the pentadactyl foot. [See

Fig. 81.] In the latter, it shifted to the outer side of this

digit, or between the third and fourth toe. [See Fig. 82.]

In the further reduction of the perissodactyl foot, the fifth

digit, being shorter than the remaining three, next left the

ground, and gradually disappeared. [Fig. 81 B.] Of the three

remaining toes, the middle or axial one was the longest, and

retaining its supremacy as greater strength and speed were

required, finally assumed the chief support of the foot [Fig. 81

C], while the outer digits left the ground, ceased to be of use,

and were lost, except as splint-bones [Fig. 81 D]. The feet of the

existing horse shows the best example of this reduction in the

Perissodactyls, as it is the most specialized known in the

Ungulates [Fig. 81 D].

In the artiodactyl foot, the reduction resulted in the gradual

diminution of the two outer of the four remaining toes, the third

and fourth doing all the work, and thus increasing in size and

power. The fifth digit, for the same reasons as in the

perissodactyl foot, first left the ground and became smaller. Next,

the second soon followed, and these two gradually ceased to be

functional, [and eventually disappeared altogether, as shown in the

accompanying drawing of the feet of still existing animals, Fig. 82

B, C, D].

The limb of the modern race-horse is a nearly perfect piece of

machinery, especially adapted to great speed on dry, level ground.

The limb of an antelope, or deer, is likewise well fitted for

rapid motion on a plain, but the foot itself is adapted to rough

mountain work as well, and it is to this advantage, in part, that

the Artiodactyls owe their present supremacy. The plantigrade

pentadactyl foot of the primitive Ungulate--and even the

perissodactyl foot that succeeded it--both belong to the past humid

period of the world's history. As the surface of the earth slowly

dried up, in the gradual desiccation still in progress, new types

of feet became a necessity, and the horse, antelope, and camel were

gradually developed, to meet the altered conditions.

The best instance of such progressive modifications in the case of

perissodactyl feet is furnished by the fossil pedigree of the existing

horse, because here, within the limits of the same continuous family

line, we have presented the entire series of modifications.

There are now known over thirty species of horse-like creatures,

beginning from the size of a fox, then progressively increasing in bulk,

and all standing in linear series in structure as in time. Confining

attention to the teeth and feet, it will be seen from the wood-cut on

page 189 that the former grow progressively longer in their sockets, and

also more complex in the patterns of their crowns. On the other hand,

the latter exhibit a gradual diminution of their lateral toes, together

with a gradual strengthening of the middle one. (See Fig. 83.) So that

in the particular case of the horse-ancestry we have a practically

complete chain of what only a few years ago were "missing links." And

this now practically completed chain shows us the entire history of what

happens to be the most peculiar, or highly specialized, limb in the

whole mammalian class--namely, that of the existing horse. Of the other

two wood-cuts, the former (Fig. 84) shows the skeleton of a very early

and highly generalized ancestor, while the other is a partial

restoration of a much more recent and specialized one. (Fig. 85.)

[Illustration: FIG. 83.--Feet and teeth in fossil pedigree of the

Horse. (After Marsh.) _a_, bones of the fore-foot; _b_, bones of the

hind-foot; _c_, radius and ulna; _d_, tibia and fibula; _e_, roots

of a tooth; _f_ and _g_, crowns of upper and lower molar teeth.]

[Illustration: FIG. 84.--_Palaeotherium_. (Lower Tertiary of Paris

Basin.)]

[Illustration: FIG. 85.--_Hipparion_. (New World Pliocene.)]

On the other hand, progressive modifications of the artiodactyl feet may

be traced geologically up to the different stages presented by living

ruminants, in some of which it has proceeded further than in others. For

instance, if we compare the pig, the deer, and the camel (Fig. 82), we

immediately perceive that the dwindling of the two rudimentary digits

has proceeded much further in the case of the deer than in that of the

pig, and yet not so far as in that of the camel, seeing that here they

have wholly disappeared. Moreover, complementary differences are to be

observed in the degree of consolidation presented by the two useful

digits. For while in the pig the two foot-bones are still clearly

distinguishable throughout their entire length, in the deer, and still

more in the camel, their union is more complete, so that they go to

constitute a single bone, whose double or compound character is

indicated externally only by a slight bifurcation at the base.

Nevertheless, if we examine the state of matters in the unborn young of

these animals, we find that the two bones in question are still

separated throughout their length, and thus precisely resemble what used

to be their permanent condition in some of the now fossil species of

hoofed mammalia.

Turning next from bones of the limb to other parts of the mammalian

skeleton, let us briefly consider the evidence of evolution that is here

likewise presented by the vertebral column, the skull, and the teeth.

As regards the vertebral column, if we examine this structure in any of

the existing hoofed animals, we find that the bony processes called

zygapophyses, which belong to each of the constituent vertebrae, are so

arranged that the anterior pair belonging to each vertebra interlocks

with the posterior pair belonging to the next vertebra. In this way the

whole series of vertebrae are connected together in the form of a chain,

which, while admitting of considerable movement laterally, is everywhere

guarded against dislocation. But if we examine the skeletons of any

ungulates from the lower Eocene deposits, we find that in no case is

there any such arrangement to secure interlocking. In all the hoofed

mammals of this period the zygapophyses are flat. Now, from this flat

condition to the present condition of full interlocking we obtain a

complete series of connecting links. In the middle Miocene period we

find a group of hoofed animals in which the articulation begins by a

slight rounding of the previously flat surfaces: later on this rounding

progressively increases, until eventually we get the complete

interlocking of the present time.

As regards teeth, and still confining attention to the hoofed mammals,

we find that low down in the geological series the teeth present on

their grinding surfaces only three simple tubercles. Later on a fourth

tubercle is added, and later still there is developed that complicated

system of ridges and furrows which is characteristic of these teeth at

the present time, and which was produced by manifold and various

involutions of the three or four simple tubercles of Eocene and lower

Miocene times. In other words, the principle of gradual improvement in

the construction of teeth, which has already been depicted as regards

the particular case of the Horse-family (Fig. 83), is no less apparent

in the pedigree of all the other mammalia, wherever the palaeontological

history is sufficiently intact to serve as a record at all.

Lastly, as regards the skull, casts of the interior show that all the

earlier mammals had small brains with comparatively smooth or

unconvoluted surfaces; and that as time went on the mammalian brain

gradually advanced in size and complexity. Indeed so small were the

cerebral hemispheres of the primitive mammals that they did not overlap

the cerebellum, while their smoothness must have been such as in this

respect to have resembled the brain of a bird or reptile. This, of

course, is just as it ought to be, if the brain, which the skull has to

accommodate, has been gradually evolved into larger and larger

proportions in respect of its cerebral hemispheres, or the upper masses

of it which constitute the seat of intelligence. Thus, if we look at the

above series of wood-cuts, which represents the comparative structure of

the brain in the existing classes of the Vertebrata, we can immediately

understand why the fossil skulls of Mammalia should present a gradual

increase in size and furrowing, so as to accommodate the general

increase of the brain in both these respects between the level marked

"maml" and that marked "man," in the last of the diagrams. (Fig. 87.)

[Illustration: FIG. 86.--Comparative series of Brains. (After Le

Conte.) The series reads from above downwards, and represents

diagrammatically the brain of a Fish, a Reptile, a Bird, a Mammal,

and a Man. In each case the letter A marks a side view, and the

letter B a top view. The small italics throughout signify the

following homologous parts: _m_, medulla; _cb_, cerebellum; _op_,

optic lobes; _cr_, cerebrum and thalamus; _ol_, olfactory lobes. The

series shows a progressive consolidation and enlargement of the

brain in general, and of the cerebrum and cerebellum in particular,

which likewise exhibit continually advancing structure in respect of

convolution. In the case of Man, these two parts of the brain have

grown to so great a size that they conceal all the other parts from

the superficial points of view represented in the diagram.]

[Illustration: FIG. 87.--Ideal section through all the above stages.

(After Le Conte.])

The tabular statement on the following diagram, which I borrow from

Prof. Cope, will serve at a glance to reveal the combined significance

of so many lines of evidence, united within the limits of the same group

of animals.

To give only one special illustration of the principle of evolution as

regards the skull, here is one of the most recent instances that has

occurred of the discovery of a missing link, or connecting form (see

Fig. 88). The fossil (B), which was found in New Jersey, stands in an

intermediate position between the stag and the elk. In the stag (A) the

skull is high, showing but little of that anterior attenuation which is

such a distinctive feature of the skull of the elk (C). The nasal bones

(N) of the former, again, are remarkably long when compared with the

similar bones of the latter, and the premaxillaries (PMX), instead of

being projected forward along the horizontal plane of the base of the

skull, are deflected sharply downward. In all these points, it will be

seen, the newly discovered form (_Cervalces_) holds an intermediate

position (B). "The skull exhibits a partial attenuation anteriorly,

the premaxillaries are directed about equally downward and forward, and

the nasal bones are measurably contracted in size. The horns likewise

furnish characters which further serve to establish this dual

relationship[18]."

[18] Heilprin, _Geological Evidences of Evolution_, pp. 73-4 (1888).

[Illustration: FIG. 88.--Skulls of--A, Canadian Stag; B, _Cervalces

Americanus_; and C, Elk. (After Heilprin.)]

Formation.

|No. of toes

| |Feet

| | |Astragalus.

| | | |Carpus and tarsus.

| | | | |Ulno-radius.

| | | | | |Superior molars.

| | | | | | |Zygapophyses.

| | | | | | | |Brain.

| | | | | | | |

Pliocene.

|1-1, 2-2

| |Digitigrade. (Plantigrade.)

| | |Grooved. (Flat.)

| | | |Interlocking. (Opposite.)

| | | | |Faceted.

| | | | | |4-tubercles, crested and cemented.

| | | | | | |Doubly involute. Singly involute.

| | | | | | | |Hemispheres larger, convoluted.

| | | | | | | |

Upper Miocene. (Loup Fork.)

|3-3, 4-4, (5-5)

| |

| | |

| | | |

| | | | |

| | | | | |

| | | | | | |

| | | | | | | |

| | | | | | | |

Middle. (John Day.)

|2-2, 3-3, 4-4

| |Digitigrade.

| | |Grooved.

| | | |Interlocking.

| | | | |Faceted. Smooth

| | | | | |4-tubercles, and crested

| | | | | | |Singly involute. Double involute.

| | | | | | | |Hemispheres larger, convoluted.

| | | | | | | |

Lower (White River.)

|3-3, 4-3

| |Digitigrade. Plantigrade.

| | |Grooved.

| | | |Interlocking.

| | | | |Smooth. Faceted.

| | | | | |4-tubercles, and crested

| | | | | | |? Singly involute.

| | | | | | | |Hemispheres small, and largeer.

| | | | | | | |

Eocene. Upper (Bridger.)

|3-3, 4-3, 4-5

| |(Digitigrade.) Plantigrade.

| | |Grooved. (Flat.)

| | | |Opposite. Interlocking.

| | | | |Smooth.

| | | | | |4-tubercles. 3-tubercles, and crested.

| | | | | | |Singly involute. Plane

| | | | | | | |Hemispheres small.

| | | | | | | |

Middle. (Wasatch.)

|4-3, 4-5, 5-5

| |Plantigrade. (Digitigrade.)

| | |Flat. (Grooved.)

| | | |Opposite. Interlocking.

| | | | |Smooth.

| | | | | |4-tubercles. 3-tubercles, a few crested.

| | | | | | |Plane. Singly involute.

| | | | | | | |Hemispheres small;

| | | | | | | |mesencephalon sometimes exposed

| | | | | | | |

Lower (Puerco.)

|5-5

| |Plantigrade.

| | |Flat.

| | | |Opposite.

| | | | |Smooth.

| | | | | |3-tubercles. (4-tubercles), none crested.

| | | | | | |Plane.

| | | | | | | |Mesencephalon exposed;

| | | | | | | |hemisphere small and smoother.

| | | | | | | |

The evidence, then, which is furnished by all parts of the vertebral

skeleton--whether we have regard to Fishes, Reptiles, Birds, or

Mammals--is cumulative and consistent. Nowhere do we meet with any

deviation or ambiguity, while everywhere we encounter similar proofs of

continuous transformation--proofs which vary only with the varying

amount of material which happens to be at our disposal, being most

numerous and detailed in those cases where the greatest number of fossil

forms has been preserved by the geological record. Here, therefore, we

may leave the vertebral skeleton; and, having presented a sample of the

evidence as yielded by horns and bones, I will conclude by glancing with

similar brevity at the case of shells--which, as before remarked,

constitute the only other sufficiently hard or permanent material to

yield unbroken evidence touching the fossil ancestry of animals.

Of course it will be understood that I am everywhere giving merely

samples of the now superabundant evidence which is yielded by

palaeontology; and, as this chapter is already a long one, I must content

myself with citing only the case of mollusk-shells, although shells of

other classes might be made to yield highly important additions to the

testimony. Moreover, even as regards the one division of mollusk-shells,

I can afford to quote only a very few cases. These, however, are in my

opinion the strongest single pieces of evidence in favour of

transmutation which have thus far been brought to light.

Near the village of Steinheim, in Wuertemberg, there is an ancient

lake-basin, dating from Tertiary times. The lake has long ago dried up;

but its aqueous deposits are extraordinarily rich in fossil shells,

especially of different species of the genus _Planorbis_. The following

is an authoritative _resume_ of the facts.

As the deposits seem to have been continuous for ages, and the

fossil shells very abundant, this seemed to be an excellent

opportunity to test the theory of derivation. With this end in

view, they have been made the subject of exhaustive study by

Hilgendorf in 1866, and by Hyatt in 1880. In passing from the

lowest to the highest strata the species change greatly and many

times, the extreme forms being so different that, were it not for

the intermediate forms, they would be called not only different

species, but different genera. And yet the gradations are so

insensible that the whole series is nothing less than a

demonstration, in this case at least, of origin of species by

derivation with modifications. The accompanying plate of successive

forms (Fig. 89), which we take from Prof. Hyatt's admirable memoir,

will show this better than any mere verbal explanation. It will be

observed that, commencing with four slight varieties--probably

sexually isolated varieties--of one species, each series shows a

gradual transformation as we go upward in the strata--i. e. onward

in time. Series I branches into three sub-series, in two of which

the change of form is extreme. Series IV is remarkable for great

increase in size as well as change in form. In the plate we give

only selected stages, but in the fuller plates of the memoir, and

still more in the shells themselves, the subtilest gradations are

found[19].

[19] Le Conte, _loc. cit._, pp. 236-7.

[Illustration: FIG. 89.--Transmutations of _Planorbis_. (After

Hyatt.)]

Here is another and more recently observed case of transmutation in the

case of mollusks.

The recent species, _Strombus accipitrinus_, still inhabits the coasts

of Florida. Its extinct prototype, _S. Leidy_, was discovered a few

years ago by Prof. Heilprin in the Pliocene formations of the interior

of Florida. The peculiar shape of the wing, and tuberculation of the

whorl, are thus proved to have grown but of a previously more conical

form of shell.

[Illustration: FIG. 90.--Transformation of _Strombus_. (After

Heilprin.) 1, 1_a_, _Strombus Leidy_ (1, typical), Pliocene; 2,

2_a_, _Strombus accipitrinus_ (2_a_ typical) Recent.]

Lastly, attention may here again be directed to the very instructive

series of shells which has already been shown in a previous chapter, and

which serves to illustrate the successive geological forms of _Paludina_

from the Tertiary beds of Slavonia, as depicted by Prof. Neumayr of

Vienna. (Fig. 1, p. 19.)

CHAPTER VI.

GEOGRAPHICAL DISTRIBUTION.

The argument from geology is the argument from the distribution of

species in time. I will next take the argument from the distribution of

species in space--that is, the present geographical distribution of

plants and animals.

Seeing that the theory of descent with adaptive modification implies

slow and gradual change of one species into another, and progressively

still more slow and gradual changes of one genus, family, or order into

another genus, family, or order, we should expect on this theory that

the organic types living on any given geographical area would be found

to resemble or to differ from organic types living elsewhere, according

as the area is connected with or disconnected from other geographical

areas. For instance, the large continental islands of Australia and New

Zealand are widely disconnected from all other lands of the world, and

deep sea soundings show that they have probably been thus disconnected,

either since the time of their origin, or, at the least, through immense

geological epochs. The theory of evolution, therefore, would expect to

find two general facts with regard to the inhabitants of these islands.

First, that the inhabitants should form, as it were, little worlds of

their own, more or less unlike the inhabitants of any other parts of the

globe. And next, that some of these inhabitants should present us with

independent information touching archaic forms of life. For it is

manifestly most improbable that the course of evolutionary history

should have run exactly parallel in the case of these isolated oceanic

continents and in continents elsewhere. Australia and New Zealand,

therefore, ought to present a very large number, not only of peculiar

species and genera, but even of families, and possibly of orders. Now

this is just what Australia and New Zealand do present. The case of the

dog being doubtful, there is an absence of all mammalian life, except

that of one of the oldest and least highly developed orders, the

Marsupials. There even occurs a unique order, still lower in the scale

of organization--so low, in fact, that it deserves to be regarded as but

nascent mammalian: I mean, of course, the Monotremata. As regards Birds,

we have the peculiar wingless forms alluded to in a previous chapter

(viz. that on Morphology); and, without waiting to go into details, it

is notorious that the faunas of Australia and New Zealand are not only

highly peculiar, but also suggestively archaic. Therefore, in both the

respects above mentioned, the anticipations of our theory are fully

borne out. But as it would take too long to consider, even cursorily,

the faunas and floras of these immense islands, I here allude to them

only for the sake of illustration. In order to present the argument from

geographical distribution within reasonable limits, I think it is best

to restrict our examination to smaller areas; for these will better

admit of brief and yet adequate consideration. But of course it will be

understood that the less isolated the region, and the shorter the time

that it has been isolated, the smaller amount of peculiarity should we

expect to meet with on the part of its present inhabitants. Or,

conversely stated, the longer and the greater the isolation, the more

peculiarity of species would our theory expect to find. The object of

the present chapter will be to show that these, and other cognate

expectations, are fully realized by facts; but, before proceeding to do

this, I must say a few words on the antecedent standing of the argument.

Where the question is, as at present, between the rival theories of

special creation and gradual transmutation, it may at first sight well

appear that no test can be at once so crucial and so easily applied as

this of comparing the species of one geographical area with those of

another, in order to see whether there is any constant correlation

between differences of type and degrees of separation. But a little

further thought is enough to show that the test is not quite so simple

or so absolute--that it is a test to be applied in a large and general

way over the surface of the whole earth, rather than one to be relied

upon as exclusively rigid in every special case.

In the first place, there is the obvious consideration that lands or

seas which are discontinuous now may not always have been so, or not for

long enough to admit of the effects of separation having been exerted to

any considerable extent upon their inhabitants. Next, there is the

scarcely less important consideration, that although land areas may long

have been separated from one another by extensive tracts of ocean,

birds and insects may more or less easily have been able to fly from

one to the other; while even non-flying animals and plants may often

have been transported by floating ice or timber, wind or water currents,

and sundry other means of dispersal. Again, there is the important

influence of climate to be taken into account. We know from geological

evidence that in the course of geological time the self-same continents

have been submitted to enormous changes of temperature--varying in fact

from polar cold to almost tropical heat; and as it is manifestly

impossible that forms of life suited to one of these climates could have

survived during the other, we can here perceive a further and most

potent cause interfering with the test of geographical distribution as

indiscriminately applied in all cases. When the elephant and

hippopotamus were flourishing in England amid the luxuriant vegetation

which these large animals require, it is evident that scarcely any one

species of either the fauna or the flora of this country can have been

the same as it was when its African climate gave place to that of

Greenland. Therefore, as Mr. Wallace observes, "If glacial epochs in

temperate lands and mild climates near the poles have, as now believed

by men of eminence, occurred several times over in the past history of

the earth, the effects of such great and repeated changes both on

migration, modification, and extinction of species, must have been of

overwhelming importance--of more importance perhaps than even the

geological changes of sea and land."

But although for these, and certain other less important reasons which I

need not wait to detail, we must conclude that the evidence from

geographical distribution is not to be regarded as a crucial test

between the rival theories of creation and evolution in all cases

indiscriminately, I must next remark that it is undoubtedly one of the

strongest lines of evidence which we possess. When we once remember

that, according to the general theory of evolution itself, the present

geographical distribution of plants and animals is "the visible outcome

or residual product of the whole past history of the earth," and,

therefore, that of the conditions determining the characters of life

inhabiting this and that particular area continuity or discontinuity

with other areas is but one,--when we remember this, we find that no

further reservation has to be made: all the facts of geographical

distribution speak with one consent in favour of the naturalistic

theory.

* * * * *

The first of these facts which I shall adduce is, that although the

geographical range of any given species is, as a rule, continuous, such

is far from being always the case. Very many species have more or less

discontinuous ranges--the mountain-hare, for instance, extending from

the Arctic regions over the greater portion of Europe to the Ural

Mountains and the Caucasus, and yet over all this enormous tract

appearing only in isolated or discontinuous patches, where there happen

to be either mountain ranges or climates cold enough to suit its nature.

Now, in all such cases of discontinuity in the range of a species the

theory of evolution has a simple explanation to offer--namely, either

that some representatives of the species have at some former period been

able to migrate from one region to the other, or else that at one time

the species occupied the whole of the range in question, but afterwards

became broken up as geographical, climatic, or other changes rendered

parts of the area unfit for the species to inhabit. Thus, for instance,

it is easy to understand that during the last cold epoch the

mountain-hare would have had a continuous range; but that as the Arctic

climate gradually receded to polar regions, the species would be able to

survive in southern latitudes only on mountain ranges, and thus would

become broken up into many discontinuous patches, corresponding with

these ranges. In the same way we can explain the occurrence of Arctic

vegetation on the Alps and Pyrenees--namely, as left behind by the

retreat of the Arctic climate at the close of the glacial period.

But now, on the other hand, the theory of special creation cannot so

well afford to render this obvious explanation of discontinuity. In the

case of the Arctic flora of the Alps, for instance, although it is true

that much of this vegetation is of an Arctic type, it is not true that

the species are all identical with those which occur in the Arctic

regions. Therefore the theory of special creation would here have to

assume that, although the now common species were left behind on the

Alps by the retreat of glaciation northwards, the peculiar Alpine

species were afterwards created separately upon the Alps, and yet

created with such close affinities to the pre-existing species as to be

included with them under the same genera. Looking to the absurdity of

this supposition, as well as of others which I need not wait to mention,

certain advocates of special creation have sought to take refuge in

another hypothesis--namely, that species which present a markedly

discontinuous range may have had a corresponding number of different

centres of creation, the same specific type having been turned down, so

to speak, on widely separated areas. But to me it seems that this

explanation presents even greater difficulty than the other. If it is

difficult to say why the Divinity should have chosen to create new

species of plants on the Alps on so precisely the same pattern as the

old, much more would it be difficult to say why, in addition to these

new species, he should also have created again the old species which he

had already placed in the Arctic regions.

* * * * *

So much, then, for discontinuity of distribution. The next general fact

to be adduced is, that there is no constant correlation between habitats

and animals or plants suited to live upon them. Of course all the

animals and plants living upon any given area are well suited to live

upon that area; for otherwise they could not be there. But the point now

is, that besides the area on which they do live, there are usually many

other areas in different parts of the globe where they might have lived

equally well--as is proved by the fact that when transported by man they

thrive as well, or even better, than in their native country. Therefore,

upon the supposition that all species were separately created in the

countries where they are respectively found, we must conclude that they

were created in only some of the places where they might equally well

have lived. Probably there is at most but a small percentage either of

plants or animals which would not thrive in some place, or places, on

the earth's surface other than that in which they occur; and hence we

must say that one of the objects of special creation--if this be the

true theory--was that of depositing species in only some among the

several parts of the earth's surface equally well suited to support

them.

Now, I do not contend that this fact in itself raises any difficulty

against the theory of special creation. But I do think that a very

serious difficulty is raised when to this fact we add another--namely,

that on every biological region we encounter species related to other

species in genera, and usually also genera related to other genera in

families. For if each of all the constituent species of a genus, and

even of a family, were separately created, we must hence conclude that

in depositing them there was an unaccountable design manifested to make

areas of distribution correspond to the natural affinities of their

inhabitants. For example, the humming-birds are geographically

restricted to America, and number 120 genera, comprising over 400

species. Hence, if this betokens 400 separate acts of creation, it

cannot possibly have been due to chance that they were all performed on

the same continent: it must have been design which led to every species

of this large family of birds having been deposited in one geographical

area. Or, to take a case where only the species of a single genus are

concerned. The rats and mice proper constitute a genus which comprises

altogether more than 100 species, and they are all exclusively

restricted to the Old World. In the New World they are represented by

another genus comprising about 70 species, which resemble their Old

World cousins in form and habits; but differ from them in dentition and

other such minor points. Now, the question is,--Why should all the 100

species have been separately created on one side of the Atlantic with

one pattern of dentition, and all the 70 species on the other side with

another pattern? What has the Atlantic Ocean got to do with any

"archetypal plan" of rats' teeth?

Or again, to recur to Australia, why should all the mammalian forms of

life be restricted to the one group of Marsupials, when we know that not

only the Rodents, such as the rabbit, but all other orders of mammals,

would thrive there equally well. And similarly, of course, in countless

other instances. Everywhere we meet with this same correlation between

areas of distribution and affinities of classification.

Now, it is at once manifest how completely this general fact harmonizes

with the theory of evolution. If the 400 species of humming-birds, for

instance, are all modified descendants of common ancestors, and if none

of their constituent individuals have ever been large enough to make

their way across the oceans which practically isolate their territory

from all other tropical and sub-tropical regions of the globe, then we

can understand why it is that all the 400 species occupy the same

continent. But on the special-creation theory we can see no reason why

the 400 species should all have been deposited in America. And, as

already observed, we must remember that this correlation between a

geographically restricted habitat and the zoological or botanical

affinities of its inhabitants, is repeated over and over and over again

in the faunas and floras of the world, so that merely to enumerate the

instances would require a separate chapter.

Furthermore, the general argument thus presented in favour of descent

with continuous modification admits of being enormously strengthened by

three different classes of additional facts.

The first is, that the correlation in question--namely, that between a

geographically restricted habitat and the zoological or botanical

affinities of its inhabitants--is not limited to the now existing

species, but extends also to the extinct. That is to say, the dead

species are allied to the living species, as we should expect that they

must be, if the latter are modified descendants of the former. On the

alternative theory, however, we have to suppose that the policy of

maintaining a correlation between geographical restriction and natural

affinity extends very much further back than even the existing species

of plants and animals; indeed we must suppose that a practically

infinite number of additional acts of separate creation were governed by

the same policy, in the case of long lines of species long since

extinct.

Thus far, then, the only answer which an advocate of special creation

can adduce is, that for some reason unknown to us such a policy may have

been more wise than it appears: it may have served some inscrutable

purpose that allied products of distinct acts of creation should all be

kept together on the same areas. Well, in answer to this unjustifiable

appeal to the argument from ignorance, I will adduce the second of the

three considerations. This is, that in cases where the geographical

areas are not restricted the policy in question fails. In other words,

where the inhabitants of an area are free to migrate to other areas, the

policy of correlating affinity with distribution is most significantly

forgotten. In this case species wander away from their native homes, and

the course of their wanderings is marked by the origination of new

species springing up en route. Now, is it reasonable to suppose that the

mere circumstance of some members of a species being able to leave their

native home should furnish any occasion for creating new and allied

species upon the tracts over which they travel, or the territories to

which they go? When the 400 existing species of humming-birds have all

been created on the same continent for some reason supposed to be

unknown, why should this reason give way before the accident of any

means of migration being furnished to humming-birds, so that they should

be able to visit, say the continents of Africa and Asia, there gain a

footing beside the sun-birds, and henceforth determine a new centre for

the separate creation of additional species of humming-birds peculiar to

the Old World--as has happened in the case of the majority of species

which, unlike the humming-birds, have been at any time free to migrate

from their original homes?

Lastly, my third consideration is, that the supposed policy in question

does not extend to affinities which are wider than those between species

and genera--more rarely to families, scarcely ever to orders, and never

to classes. In other words, nature shows a double correlation in her

geographical distribution of organic types:--first, that which we have

already considered between geographical restriction and natural

affinity among inhabitants of the same areas; second, another of a more

detailed character between _degrees_ of geographical restriction and

_degrees_ of natural affinity. The more distant the affinity, the more

general is the extension. This, of course, is what we should expect on

the theory of descent with modification, because the more distant the

affinity, and therefore, _ex hypothesi_, the larger and the older the

original group of organisms, the greater must be the chance of

dispersal. The 400 species of humming-birds may well be unable to

migrate from their native continent; but it would indeed have been an

unaccountable fact if no other species of all the class of birds had

ever been able to have crossed the Atlantic Ocean. Thus, on the theory

of evolution, we can well understand the second correlation now before

us--namely, between remoteness of affinity and generality of

dispersal,--so that there is no considerable portion of the habitable

globe without representatives of all the classes of animals, few

portions without representatives of all the orders, but many portions

without many of the families, innumerable portions without innumerable

genera, and, of course, all portions without the great majority of

species. Now, while this general correlation thus obviously supports the

theory of natural descent with progressive modification, it makes

directly against the opposite theory of special creation. For we have

recently seen that when we restrict our view to the case of species and

genera, the theory of special creation is obliged to suppose that for

some inscrutable reason the Deity had regard to systematic affinity

while determining on what large areas to create his species[20]. But

now we see that he must be held to have neglected this inscrutable

reason (whatever it was) when he passed beyond the range of genera--and

this always in proportion to the remoteness of systematic affinity on

the part of the species concerned.

[20] I say "_large_ areas" for the sake of argument; but the same

correlation between distribution and affinity extends likewise to

_small_ areas where only _small_ differences of affinity are

concerned. Thus, for instance, speaking of smaller areas, Moritz

Wagner says:--"The broader and more rapid the river, the higher and

more regular the mountain-chain, the calmer and more extensive the

sea, the more considerable, as a general rule, will be the taxonomic

separation between the populations"; and he shows that, in

correlation with such differences in the _degrees_ of separation,

are the _degrees_ of diversification--i. e., the _numbers_ of

species, and even of varieties, which these topographical barriers

determine.

I cannot well conceive a _reductio ad absurdum_ more complete than this.

But, having now presented these most general facts of geographical

distribution in their relation to the issue before us, we may next

proceed to consider a few illustrations of them in detail, for in this

way I think that their overwhelming weight may become yet more

abundantly apparent.

* * * * *

It will assist us in dealing with these detailed illustrations if we

begin by considering the means of dispersal of organisms from one place

to another. Of course the most ordinary means is that of continuous

wandering, or emigration; but where geographical barriers of any kind

have to be surmounted, organisms may only be able to pass them by more

exceptional and accidental means. The principal barriers of a

geographical kind are oceans, rivers, mountain-chains, and

desert-tracts, in the case of terrestrial organisms; and, in the case

of aquatic organisms, the presence of land. But it is to be observed

that, as regards marine organisms, any considerable difference in the

temperature of the water may constitute a barrier as effectual as the

presence of land; and also that, in the case of all shallow-water

faunas, a tract of deep ocean constitutes almost as complete a barrier

as it does to terrestrial faunas.

Now, the means whereby barriers admit of being accidentally or

occasionally surmounted are, of course, various; and they differ in the

case of different organisms. Birds, bats, and insects, on account of

their powers of flight, are particularly apt to be blown out great

distances to sea, and hence of all animals are most likely to become the

involuntary colonists of distant shores. Floating timber serves to

convey seeds and eggs of small animals over great distances; and Darwin

has shown that many kinds of seeds are able of themselves to float for

more than a month in sea-water without losing their powers of

germination. For instance, out of 87 kinds, 64 germinated after an

immersion of 28 days, and a few survived an immersion of 137 days. As a

result of all his experiments he concludes, that the seeds of at least

ten per cent. of the species of plants of any country might be floated

by sea-currents during 28 days, without losing their powers of

germination; and this, at the average rate of flow of several Atlantic

currents, would serve to transport the seeds to a distance of at least

900 miles. Again, he proved that even seeds which are quickly destroyed

by contact with sea-water admit of being successfully transported during

30 days, if they be contained within the crop of a dead bird. He also

proved that living birds are most active agents in the work of

dissemination, and this not only by taking seeds into their crops

(where, so long as they remain, the seeds are uninjured), but likewise

by carrying seeds (and even young mollusks) attached to their feet and

feathers. In the course of these experiments he found that a small

cup-full of mud, which he gathered from the edges of three ponds in

February, was so charged with seeds that when sown in the ground these

few ounces of mud yielded no less than 537 plants, belonging to many

different species. It is therefore evident what opportunities are thus

afforded for the transportation of seeds on the feet and bills of

wading-birds. Lastly, floating ice is well known to act as a carrier of

any kind of life which may prove able to survive this mode of transit.

Such being the nature of geographical barriers, and the means that

organisms of various kinds may occasionally have of overcoming them, I

will now give a few detailed illustrations of the argument from

geographical distribution, as previously presented in its general form.

To begin with aquatic animals. As Darwin remarks, "the marine

inhabitants of the Eastern and Western shores of South America are very

distinct; with extremely few shells, crustacea, or echinodermata in

common." Again, westward of the shores of America, a wide space of open

ocean extends, which, as we have seen, furnishes as effectual a barrier

as does the land to any emigration of shallow-water animals. Now, as

soon as this reach of deep water is passed, we meet in the eastern

islands of the Pacific with another and totally distinct fauna. "So that

three marine faunas range northward and southward in parallel lines not

far from each other, under corresponding climates": they are, however,

"separated from each other by impassable barriers, either of land or

open sea": and it is in exact coincidence with the course of these

barriers that we find so remarkable a differentiation of the faunas[21].

Obviously, therefore, it is impossible to suggest that this correlation

is accidental. Altogether many thousands of species are involved, and

within this comparatively limited area they are sharply marked off into

three groups as to their natural affinities, and into three groups as to

their several basins. Hence, if all these species were separately

created, there is no escape from the conclusion that for some reason or

another the act of creation was governed by the presence of these

barriers, so that species deposited on the Eastern shores of South

America were formed with one set of natural affinities, while species

deposited on the Western shore were formed with another set; and

similarly with regard to the third set of species in the third basin,

which, extending over a whole hemisphere to the coast of Africa without

any further barrier, nowhere presents, over this vast area, any other

case of a distinct marine fauna. But what conceivable reason can there

have been thus to consult these geographical barriers in the original

creation of specific types? Even if such a case stood alone, it would

be strongly suggestive of error on the part of the special creation

theory. But let us take another case, this time from fresh-water faunas.

[21] The only exception is in the case of the fish on each side of

the isthmus of panama, where about 30 per cent, of the species are

identical. But it is possible enough that at some previous time this

narrow isthmus may have been even narrower than at present, if not

actually open. At all events, the fact that this partial exception

occurs just where the land-barrier is so narrow, is more suggestive

of migration than of independent creation.

Although the geographical distribution of fresh-water fish and

fresh-water shells is often surprisingly extensive and apparently

capricious, this may be explained by the means of dispersal being here

so varied--not only aquatic birds, floods, and whirlwinds, but also

geographical changes of water-shed having all assisted in the process.

Moreover, in some cases it is possible that the habits of more widely

distributed fresh-water fish may have originally been wholly or partly

marine--which, of course, would explain the existing discontinuity of

their existing fresh-water distribution. But, be this as it may (and it

is not a question that affects the issue between special creation and

gradual evolution, since it is only a question as to how a given species

has been dispersed from its original home, whether or not in that home

it was specially created), the point I desire to bring forward is, that

where we find a barrier to the emigration of fresh-water forms which is

more formidable than a thousand miles of ocean--a barrier over which

neither water-fowl nor whirlwinds are likely to pass, and which is above

the reach of any geological changes of water-shed,--where we find such a

barrier, we always find a marked difference in the fresh-water faunas on

either side of it. The kind of barrier to which I allude is a high

mountain-chain. It may be only a few miles wide; yet it exercises a

greater influence on the diversification of specific types, where

fresh-water faunas are concerned, than almost any other. But why should

this be the case on any intelligible theory of special creation? Why, in

the depositing of species of newly created fresh-water fish, should the

presence of an impassable mountain-chain have determined so uniformly a

difference of specific affinity on either side of it? The question, so

far as I can see, does not admit of an answer from any reasonable

opponent.

* * * * *

Turning now from aquatic organisms to terrestrial, the body of facts

from which to draw is so large, that I think the space at my disposal

may be best utilized by confining attention to a single division of

them--that, namely, which is furnished by the zoological study of

oceanic islands.

In the comparatively limited--but in itself extensive--class of facts

thus presented, we have a particularly fair and cogent test as between

the alternative theories of evolution and creation. For where we meet

with a volcanic island, hundreds of miles from any other land, and

rising abruptly from an ocean of enormous depth, we may be quite sure

that such an island can never have formed part of a now submerged

continent. In other words, we may be quite sure that it always has been

what it now is--an oceanic peak, separated from all other land by

hundreds of miles of sea, and therefore an area supplied by nature for

the purpose, as it were, of testing the rival theories of creation and

evolution. For, let us ask, upon these tiny insular specks of land what

kind of life should we expect to find? To this question the theories of

special creation and of gradual evolution would agree in giving the

same answer up to a certain point. For both theories would agree in

supposing that these islands would, at all events in large part, derive

their inhabitants from accidental or occasional arrivals of wind-blown

or water-floated organisms from other countries--especially, of course,

from the countries least remote. But, after agreeing upon this point,

the two theories must part company in their anticipations. The

special-creation theory can have no reason to suppose that a small

volcanic island in the midst of a great ocean should be chosen as the

theatre of any extraordinary creative activity, or for any particularly

rich manufacture of peculiar species to be found nowhere else in the

world. On the other hand, the evolution theory would expect to find that

such habitats are stocked with more or less peculiar species. For it

would expect that when any organisms chanced to reach a wholly isolated

refuge of this kind, their descendants should forthwith have started

upon an independent course of evolutionary history. Protected from

intercrossing with any members of their parent species elsewhere, and

exposed to considerable changes in their conditions of life, it would

indeed be fatal to the general theory of evolution if these descendants,

during the course of many generations, were not to undergo appreciable

change. It has happened on two or three occasions that European rats

have been accidentally imported by ships upon some of these islands, and

even already it is observed that their descendants have undergone a

slight change of appearance, so as to constitute them what naturalists

call local varieties. The change, of course, is but slight, because the

time allowed for it has been so short. But the longer the time that a

colony of a species is thus completely isolated under changed conditions

of life the greater, according to the evolution theory, should we expect

the change to become. Therefore, in all cases where we happen to know,

from independent evidence of a geological kind, that an oceanic island

is of very ancient formation, the evolution theory would expect to

encounter a great wealth of peculiar species. On the other hand, as I

have just observed, the special-creation theory can have no reason to

suppose that there should be any correlation between the age of an

oceanic island and the number of peculiar species which it may be found

to contain.

Therefore, having considered the principles of geographical distribution

from the widest or most general point of view, we shall pass to the

opposite extreme, and consider exhaustively, or in the utmost possible

detail, the facts of such distribution where the conditions are best

suited to this purpose--that is, as I have already said, upon oceanic

islands, which may be metaphorically regarded as having been formed by

nature for the particular purpose of supplying naturalists with a

crucial test between the theories of creation and evolution. The

material upon which my analysis is to be based will be derived from the

most recent works upon geographical distribution--especially from the

magnificent contributions to this department of science which we owe to

the labours of Mr. Wallace. Indeed, all that follows may be regarded as

a condensed filtrate of the facts which he has collected. Even as thus

restricted, however, our subject-matter would be too extensive to be

dealt with on the present occasion, were we to attempt an exhaustive

analysis of the floras and faunas of all oceanic islands upon the face

of the globe. Therefore, what I propose to do is to select for such

exhaustive analysis a few of what may be termed the most oceanic of

oceanic islands--that is to say, those oceanic islands which are most

widely separated from mainlands, and which, therefore, furnish the most

unquestionable of test cases as between the theories of special creation

and genetic descent.

* * * * *

_Azores._--A group of volcanic islands, nine in number, about 900 miles

from the coast of Portugal, and surrounded by ocean depths of 1,800 to

2,500 fathoms. There is geological evidence that the origin of the group

dates back at least as far as Miocene times. There is a total absence of

all terrestrial Vertebrata, other than those which are known to have

been introduced by man. Flying animals, on the other hand, are abundant;

namely, 53 species of birds, one species of bat, a few species of

butterflies, moths, and hymenoptera, with 74 species of indigenous

beetles. All these animals are unmodified European species, with the

exception of one bird and many of the beetles. Of the 74 indigenous

species of the latter, 36 are not found in Europe; but 19 are natives of

Madeira or the Canaries, and 3 are American, doubtless transplanted by

drift-wood. The remaining 14 species occur nowhere else in the world,

though for the most part they are allied to other European species.

There are 69 known species of land-shells, of which 37 are European, and

32 peculiar, though all allied to European forms. Lastly, there are 480

known species of plants, of which 40 are peculiar, though allied to

European species.

_Bermudas._--A small volcanic group of islands, 700 miles from North

Carolina. Although there are about 100 islands in the group, their total

area does not exceed 50 square miles. The group is surrounded by water

varying in depth from 2,500 to 3,800 fathoms. The only terrestrial

Vertebrate (unless the rats and mice are indigenous) is a lizard allied

to an American form, but specifically distinct from it, and therefore a

solitary species which does not occur anywhere else in the world. None

of the birds or bats are peculiar, any more than in the case of the

Azores; but, as in that case, a large percentage of the land-shells are

so--namely, at least one quarter of the whole. Neither the botany nor

the entomology of this group has been worked out; but I have said enough

to show how remarkably parallel are the cases of these two volcanic

groups of islands situated in different hemispheres, but at about the

same distance from large continents. In both there is an extraordinary

paucity of terrestrial vertebrata, and of any peculiar species of bird

or beast. On the other hand, there is in both a marvellous wealth of

peculiar species of insects and land-shells. Now these correlations are

all abundantly intelligible. It is a difficult matter for any

terrestrial animal to cross 900, or even 700, miles of ocean: therefore

only one lizard has succeeded in doing so in one of the two parallel

cases; and, living cut off from intercrossing with its parent form, the

descendants of that lizard have become modified so as to constitute a

peculiar species. But it is more easy for large flying animals to cross

those distances of ocean: consequently, there is only one instance of a

peculiar species of bird or bat--namely, a bull-finch in the Azores,

which, being a small land-bird, is not likely ever to have had any other

visitors from its original parent species coming over from Europe to

keep up the original breed. Lastly, it is very much more easy for

insects and land-mollusca to be conveyed to such islands by wind and

floating timber than it is for terrestrial mammals, or even than it is

for small birds and bats; but yet such means of transit are not

sufficiently sure to admit of much recruiting from the mainland for the

purpose of keeping up the specific types. Consequently, the insects and

the land-shells present a much greater proportion of peculiar

species--namely, one half and one fourth of the land-shells in the one

case, and one eighth of the beetles in the other. All these

correlations, I say, are abundantly intelligible on the theory of

evolution; but who shall explain, on the opposite theory, why orders of

beetles and land-mollusca should have been chosen from among all other

animals for such superabundant creation on oceanic islands, so that in

the Azores alone we find no less than 32 of the one and 14 of the other?

And, in this connexion, I may again allude to the peculiar species of

beetles in the island of Madeira. Here there are an enormous number of

peculiar species, though they are nearly all related to, or included

under the same genera as, beetles on the neighbouring continent. Now, as

we have previously seen, no less than 200 of these species have lost the

use of their wings. Evolutionists explain this remarkable fact by their

general laws of degeneration under disuse, and the operation of natural

selection, as will be shown later on; but it is not so easy for special

creationists to explain why this enormous number of peculiar species of

beetles should have been deposited on Madeira, all allied to beetles on

the nearest continent, and nearly all deprived of the use of their

wings. And similarly, of course, with all the peculiar species of the

Bermudas and the Azores. For who will explain, on the theory of

independent creation, why all the peculiar species, both of animals and

plants, which occur on the Bermudas should so unmistakably present

American affinities, while those which occur on the Azores no less

unmistakably present European affinities? But to proceed to other, and

still more remarkable, cases.

_The Galapagos Islands._--This archipelago is of volcanic origin,

situated under the equator between 500 and 600 miles from the West Coast

of South America. The depth of the ocean around them varies from 2,000

to 3,000 fathoms or more. This group is of particular interest, from the

fact that it was the study of its fauna which first suggested to

Darwin's mind the theory of evolution. I will, therefore, begin by

quoting a short passage from his writings upon the zoological relations

of this particular fauna.

Here almost every product of the land and of the water bears the

unmistakeable stamp of the American continent. There are twenty-six

land birds; of these, twenty-one, or perhaps twenty-three, are

ranked as distinct species, and would commonly be assumed to have

been here created; yet the close affinity of most of these birds to

American species is manifest in every character, in their habits,

gestures, and tones of voice. So it is with the other animals, and

with a large proportion of the plants, as shown by Dr. Hooker in

his admirable Flora of this archipelago. The naturalist, looking at

the inhabitants of these volcanic islands in the Pacific, distant

several hundred miles from the continent, feels that he is standing

on American land. Why should this be so? Why should the species

which are supposed to have been created in the Galapagos

Archipelago, and nowhere else, bear so plainly the stamp of

affinity to those created in America? There is nothing in the

conditions of life, in the geological nature of the islands, in

their height or climate, or in the proportions in which the several

classes are associated together, which closely resembles the

conditions of the South American coast; in fact, there is a

considerable dissimilarity in all these respects. On the other

hand, there is a considerable degree of resemblance in the volcanic

nature of the soil, in the climate, height, and size of the

islands, between the Galapagos and Cape de Verde Archipelagoes; but

what an entire and absolute difference in their inhabitants! The

inhabitants of the Cape de Verde Islands are related to those of

Africa, like those of the Galapagos to America. Facts such as these

admit of no sort of explanation on the ordinary view of independent

creation; whereas on the view here maintained, it is obvious that

the Galapagos Islands would be likely to receive colonists from

America, and the Cape de Verde Islands from Africa; such colonists

would be liable to modification--the principle of inheritance still

betraying their original birthplace[22].

[22] _origin of species_, pp. 353-4.

The following is a synopsis of the fauna and flora of this archipelago,

so far as at present known. The only terrestrial vertebrates are two

peculiar species of land-tortoise, and one extinct species; five species

of lizards, all peculiar--two of them so much so as to constitute a

peculiar genus;--and two species of snakes, both closely allied to South

American forms. Of birds there are 57 species, of which no less than 38

are peculiar; and all the non-peculiar species, except one, belong to

aquatic tribes. The true land birds are represented by 31 species, of

which all, except one, are peculiar; while more than half of them go to

constitute peculiar genera. Moreover, while they are all unquestionably

allied to South American forms, they present a beautiful series of

gradations, "from perfect identity with the continental species, to

genera so distinct that it is difficult to determine with what forms

they are most nearly allied; and it is interesting to note that this

diversity bears a distinct relation to the probabilities of, and

facilities for, migration to the islands. The excessively abundant

rice-bird, which breeds in Canada, and swarms over the whole United

States, migrating to the West Indies and South America, visiting the

distant Bermudas almost every year, and extending its range as far as

Paraquay, is the only species of land-bird which remains completely

unchanged in the Galapagos; and we may therefore conclude that some

stragglers of the migrating host reach the islands sufficiently often to

keep up the purity of the breed[23]." Again, of the thirty peculiar

land-birds, it is observable that the more they differ from any other

species or genera on the South American continent, the more certainly

are they found to have their nearest relations among those South

American forms which have the more restricted range, and are therefore

the least likely to have found their way to the islands with any

frequency.

[23] Wallace, _Island Life_, pp. 271-2.

The insect fauna of the Galapagos islands is scanty, and chiefly

composed of beetles. These number 35 species, which are nearly all

peculiar, and in some cases go to constitute peculiar genera. The same

remarks apply to the twenty species of land-shells. Lastly, of the total

number of flowering plants (332 species) more than one half (174

species) are peculiar. It is observable in the case of these peculiar

species of plants--as also of the peculiar species of birds--that many

of them are restricted to single islands. It is also observable that,

with regard both to the fauna and flora, the Galapagos Islands as a

whole are very much richer in peculiar species than either the Azores or

Bermudas, notwithstanding that both the latter are considerably more

remote from their nearest continents. This difference, which at first

sight appears to make against the evolutionary interpretation, really

tends to confirm it. For the Galapagos Islands are situated in a calm

region of the globe, unvisited by those periodic storms and hurricanes

which sweep over the North Atlantic, and which every year convey some

straggling birds, insects, seeds, &c., to the Azores and Bermudas.

Notwithstanding their somewhat greater isolation geographically,

therefore, the Azores and Bermudas are really less isolated biologically

than are the Galapagos Islands; and hence the less degree of peculiarity

on the part of their endemic species. But, on the theory of special

creation, it is impossible to understand why there should be any such

correlation between the prevalence of gales and a comparative inertness

of creative activity. And, as we have seen, it is equally impossible on

this theory to understand why there should be a further correlation

between the _degree_ of peculiarity on the part of the isolated

species, and the degree in which their nearest allies on the mainland

are there confined to narrow ranges, and therefore less likely to keep

up any biological communication with the islands.

_St. Helena._--A small volcanic island, ten miles long by eight wide,

situated in mid-ocean, 1100 miles from Africa, and 1800 from South

America. It is very mountainous and rugged, bounded for the most part by

precipices, rising from ocean depths of 17,000 feet, to a height above

the sea-level of nearly 3,000. When first discovered it was richly

clothed with forests; but these were all destroyed by human agency

during the 16th, 17th and 18th centuries. The records of civilization

present no more lamentable instance of this kind of destruction. From a

merely pecuniary point of view the abolition of these primeval forests

has proved an irreparable loss; but from a scientific point of view the

loss is incalculable. These forests served to harbour countless forms of

life, which extended at least from the Miocene age, and which, having

found there an ocean refuge, survived as the last remnants of a remote

geological epoch. In those days, as Mr. Wallace observes, St. Helena

must have formed a kind of natural museum or vivarium of archaic species

of all classes, the interest of which we can now only surmise from the

few remnants of those remnants, which are still left among the more

inaccessible portions of the mountain peaks and crater edges. These

remnants of remnants are as follows.

There is a total absence of all indigenous mammals, reptiles,

fresh-water fish, and true land-birds. There is, however, a species of

plover, allied to one in South Africa; but it is specifically distinct,

and therefore peculiar to the island. The insect life, on the other

hand, is abundant. Of beetles no less than 129 species are believed to

be aboriginal, and, with one single exception, the whole number are

peculiar to the island. "But in addition to this large amount of

specific peculiarity (perhaps unequalled anywhere else in the world),

the beetles of this island are remarkable for their generic isolation,

and for the altogether exceptional proportion in which the great

divisions of the order are represented. The species belong to 39 genera,

of which no less than 25 are peculiar to the island; and many of these

are such isolated forms that it is impossible to find their allies in

any particular country[24]." More than two-thirds of all the species

belong to the group of weevils--a circumstance which serves to explain

the great wealth of beetle-population, the weevils being beetles which

live in wood, and St. Helena having been originally a densely wooded

island. This circumstance is also in accordance with the view that the

peculiar insect fauna has been in large part evolved from ancestors

which reached the island by means of floating timber; for, of course, no

explanation can be suggested why special creation of this highly

peculiar insect fauna should have run so disproportionately into the

production of weevils. About two-thirds of the whole number of beetles,

or over 80 species, show no close affinity with any existing insects,

while the remaining third have some relations, though often very remote,

with European and African forms. That this high degree of peculiarity

is due to high antiquity is further indicated, according to our theory,

by the large number of species which some of the types comprise. Thus,

the 54 species of _Cossonidae_ may be referred to three types; the 11

species of _Bembidium_ form a group by themselves; and the _Heteromera_

form two groups. "Now, each of these types may well be descended from a

single species, which originally reached the island from some other

land; and the great variety of generic and specific forms into which

some of them have diverged is an indication, and to some extent a

measure, of the remoteness of their origin[25]." But, on the

counter-supposition that all these 128 peculiar species were separately

created to occupy this particular island, it is surely unaccountable

that they should thus present such an arborescence of natural affinities

amongst themselves.

[24] Wallace, _Island Life_, p. 287.

[25] Wallace, _Island Life_, p. 287.

Passing over the rest of the insect fauna, which has not yet been

sufficiently worked out, we next find that there are only 20 species of

indigenous land-shells--which is not surprising when we remember by what

enormous reaches of ocean the island is surrounded. Of these 20 species

no less than 13 have become extinct, three are allied to European

species, while the rest are so highly peculiar as to have no near allies

in any other part of the globe. So that the land-shells tell exactly the

same story as the insects.

Lastly, the plants likewise tell the same story. The truly indigenous

flowering plants are about 50 in number, besides 26 ferns. Forty of the

former and ten of the latter are peculiar to the island, and, as Sir

Joseph Hooker tells us, "cannot be regarded as very close specific

allies of any other plants at all" Seventeen of them belong to peculiar

genera, and the others all differ so markedly as species from their

congeners, that not one comes under the category of being an insular

form of a continental species. So that with respect to its plants no

less than with respect to its animals, we find that the island of St.

Helena constitutes a little world of unique species, allied among

themselves, but diverging so much from all other known forms that in

many cases they constitute unique genera.

_Sandwich Islands._--These are an extensive group of islands, larger

than any we have hitherto considered--the largest of the group being

about the size of Devonshire. The entire archipelago is volcanic, with

mountains rising to a height of nearly 14,000 feet. The group is

situated in the middle of the North Pacific, at a distance of

considerably over 2,000 miles from any other land, and surrounded by

enormous ocean depths. The only terrestrial vertebrata are two lizards,

one of which constitutes a peculiar genus. There are 24 aquatic birds,

five of which are peculiar; four birds of prey, two of which are

peculiar; and 16 land-birds, all of which are peculiar. Moreover, these

16 land-birds constitute no less than 10 peculiar genera, and even one

peculiar family of five genera. This is an amount of peculiarity far

exceeding that of any other islands, and, of course, corresponds with

the great isolation of this archipelago. The only other animals which

have here been carefully studied are the land-shells, and these tell the

same story as the birds. For there are no less than 400 species which

are all, without any exception, peculiar; while about three-quarters of

them go to constitute peculiar genera. Again, of the plants, 620 species

are believed to be endemic; and of these 377 are peculiar, yielding no

less than 39 peculiar genera.

* * * * *

Prejudice apart, I think we must all now agree that it is needless to

continue further this line of proof. I have chosen the smallest and most

isolated islands for the purposes of our present argument, first because

these furnish the most crucial kind of test, and next because they best

admit of being dealt with in a short space. But, if necessary, a vast

amount of additional material could be furnished, not only from other

small oceanic islands, but still more from the largest islands of the

world, such as Australia and New Zealand. However, after the detailed

inventories which have now been given in the case of some of the smaller

islands most remote from mainlands, we may well be prepared to accept it

as a general law, that _wherever_ there is evidence of land-areas having

been for a long time separated from other land-areas, there we meet with

a more or less extraordinary profusion of unique species, often running

up into unique genera. And, in point of fact, so far as naturalists have

hitherto been able to ascertain, _there is no exception to this general

law in any region of the globe_. Moreover, there is everywhere a

constant correlation between the _degree_ of this peculiarity on the

part of the fauna and flora, and the _time_ during which they have been

isolated. Thus, for instance, among the islands which I have called

into evidence, those that are at once the most isolated and give

independent proofs of the highest antiquity, are the Galapagos Islands,

the Sandwich Islands, and St. Helena. Now, if we apply the method of

tabular analysis to these three cases, we obtain the following most

astonishing results. For the sake of simplicity I will omit the

enumeration of peculiar genera, and confine attention to peculiar

species. Moreover, I will consider only terrestrial animals; for, as we

have already seen, aquatic animals are so much more likely to reach

oceanic islands that they do not furnish nearly so fair a test of the

evolutionary hypothesis.

PECULIAR SPECIES.

+------------+---------+----------+-----------+----------+----------+

| | Shells. | Insects. | Reptiles. | Birds. | Mammals. |

| +---------+----------+-----------+----------+----------+

| Sandwich. | 400 | ? | 2 | 16 | 0 |

| Galapagos | 15 | 35 | 10 | 30 | 0 |

| St. Helena | 20 | 128 | 0 | 1 | 0 |

+------------+---------+----------+-----------+----------+----------+

| Totals. | 435 | 163 | 12 | 47 | 0 |

+------------+---------+----------+-----------+----------+----------+

NON-PECULIAR SPECIES.

+------------+---------+----------+-----------+----------+----------+

| | Shells. | Insects. | Reptiles. | Birds. | Mammals. |

| +---------+----------+-----------+----------+----------+

| Sandwich. | 0 | ? | 0 | 0 | 0 |

| Galapagos | ? | ? | 0 | 1 | 0 |

| St. Helena | 0 | ? | 0 | 0 | 0 |

+------------+---------+----------+-----------+----------+----------+

| Totals. | 0 | ? | 0 | 1 | 0 |

+------------+---------+----------+-----------+----------+----------+

From this synopsis we perceive that out of a total of 658 species of

terrestrial animals known to inhabit these three oceanic territories,

all are peculiar, with the exception of a single land-bird which is

found in the Galapagos Islands. This is the rice-bird, so very abundant

on the American continent that its representatives must not unfrequently

become the involuntary colonists of the Archipelago. There are, however,

a few species of non-peculiar insects inhabiting the Sandwich and

Galapagos Islands, the exact number of which is doubtful, and on this

account are not here quoted. But at most they would be represented by

units, and therefore do not affect the general result. Lastly, the

remarkable fact will be noted, that there is no single representative of

the mammalian class in any of these islands.

If we turn next to consider the case of plants, we obtain the following

result:--

+-----------+-----------+--------------+

| |_Peculiar |_Non-peculiar |

| | Species._ | Species._ |

+-----------|-----------|--------------+

|Sandwich | 377 | 243 |

|Galapagos | 174 | 158 |

|St. Helena | 50 | 26 |

| | ---- | ---- |

| Totals | 601 | 427 |

+-----------+-----------+--------------+

So that by adding together peculiar species both of land-animals and

plants, we find that on these three limited areas alone there are 1258

forms of life which occur nowhere else upon the globe--not to speak of

the peculiar aquatic species, nor of the presumably large number of

peculiar species of all kinds not hitherto discovered in these

imperfectly explored regions.

Now let us compare these facts with those which are presented by the

faunas and floras of islands less remote from continents, and known

from independent geological evidence to be of comparatively recent

origin--that is, to have been separated from their adjacent mainlands in

comparatively recent times, and therefore as islands to be comparatively

young. The British Isles furnish as good an instance as could be chosen,

for they together comprise over 1000 islands of various sizes, which are

nowhere separated from one another by deep seas, and in the opinion of

geologists were all continuous with the European continent since the

glacial period.

BRITISH ISLES.

NON-PECULIAR SPECIES.

+---------+---------+----------+-----------+---------+---------+

| | Land | | Reptiles | Land | Land |

| Plants. | Shells. | Insects. | and | Birds. | Mammals.|

| | | | Amphibia. | | |

+---------+---------+----------+-----------+---------+---------+

| 1462 | 83 | 12,551 | 13 | 130 | 40 |

+---------+---------+----------+-----------+---------+---------+

PECULIAR SPECIES.

+---------+---------+----------+-----------+---------+---------+

| | Land | | Reptiles | Land | Land |

| Plants. | Shells. | Insects. | and | Birds. | Mammals.|

| | | | Amphibia. | | |

+---------+---------+----------+-----------+---------+---------+

| 46 | 4 | 149 | 0 | 1 | 0 |

+---------+---------+----------+-----------+---------+---------+

Total Peculiar Plants 46

Total Peculiar Animals 154

----

Grand Total 200

I have drawn up this table in the most liberal manner possible,

including as peculiar species forms which many naturalists regard as

merely local varieties. But, even as thus interpreted, how wonderful is

the contrast between the 1000 islands of Great Britain and the single

volcanic rock of St. Helena, where almost all the animals and about half

the plants are peculiar, instead of about 1/80 of the animals, and 1/30

of the plants. Of course, if no peculiar species of any kind had

occurred in the British Isles, advocates of special creation might have

argued that it was, so to speak, needless for the Divinity to have added

any new species to those European forms which fully populated the

islands at the time when they were separated from the continent. But, as

the matter stands, advocates of special creation must face the fact that

a certain small number of new and peculiar species have been formed on

the British Isles; and, therefore, that creative activity has not been

wholly suspended in their case. Why, then, has it been so meagre in this

case of a thousand islands, when it has proved so profuse in the case of

all single islands more remote from mainlands, and presenting a higher

antiquity? Or why should the Divinity have thus appeared so uniformly to

consult these merely accidental circumstances of space and time in the

depositing of his unique specific types? Do not such facts rather speak

with irresistible force in favour of the view, that while all ancient

and solitary islands have had time enough, and separation enough, to

admit of distinct histories of evolution having been written in their

living inhabitants, no one of the thousand islands of Great Britain has

had either time enough, or separation enough, to have admitted of more

than some of the first pages of such a history having been commenced?

But this allusion to Great Britain introduces us to another point. It

will have been observed that, unlike oceanic islands remote from

mainlands, Great Britain is well furnished both with reptiles (including

amphibia) and mammals. For there is no instance of any oceanic island

situated at more than 300 miles from a continent where any single

species of the whole class of mammals is to be found, excepting species

of the only order which is able to fly--namely, the bats. And the same

has to be said of frogs, toads, and newts, whose spawn is quickly killed

by contact with sea-water, and therefore could never have reached remote

islands in a living state. Hence, on evolutionary principles; it is

quite intelligible why oceanic islands should not present any species of

mammals or batrachians--peculiar or otherwise,--save such species of

mammals as are able to fly. But on the theory of special creation we can

assign no reason why, notwithstanding the extraordinary profusion of

unique types of other kinds which we have seen to occur on oceanic

islands, the Deity should have made this curious exception to the

detriment of all frogs, toads, newts, and mammals, save only such as are

able to fly. Or, if any one should go so far to save a desperate

hypothesis as to maintain that there must have been some hidden reason

why batrachians and quadrupeds were not specially created on oceanic

islands, I may mention another small--but in this relation a most

significant--fact. This is that on some of these islands there occur

certain peculiar species of plants, the seeds of which are provided with

numerous tiny hooks, obviously and beautifully adapted--like those on

the seeds of allied plants elsewhere--to catch the wool or hair of

moving quadrupeds, and so to further their own dissemination. But, as we

have just seen, there are no quadrupeds in the islands to meet these

beautiful adaptations on the part of the plants; so that special

creationists must resort to the almost impious supposition that in these

cases the Deity has only carried out half his plan, in that while he

made an elaborate provision for these uniquely created species of

plants, which depended for its efficiency on the presence of quadrupeds,

he nevertheless neglected to place any quadrupeds on the islands where

he had placed the plants. Such one-sided attempts at adaptation surely

resolve the thesis of special creation to a _reductio ad absurdum_; and

hence the only reasonable interpretation of them is, that while the

seeds of allied or ancestral plants were able to float to the islands,

no quadrupeds were ever able over so great a distance to swim.

* * * * *

Although much more evidence might still be given under the head of

geographical distribution, I must now close with a brief summary of the

main points that have been adduced.

After certain preliminary considerations, I began by noticing that the

theory of evolution has a much more intelligible account to give than

has its rival of the facts of discontinuous distribution--the Alpine

flora, for instance, being allied to the Arctic, not because the same

species were separately created in both places, but because during the

glacial period these species extended all over Europe, and were left

behind on the Alps as the Arctic flora receded northwards--which was

sufficiently long ago to explain why some of the Alpine species are

unique, though closely allied to Arctic forms.

Next we saw that, although living things are always adapted to the

climates under which they live (since otherwise they could not live

there at all), it is equally true that, as a rule, besides the area on

which they do live, there are many other areas in different parts of the

globe where they might have lived equally well. Consequently we must

conclude that, if all species were separately created, many species were

severally created on only one among a number of areas where they might

equally well have thrived. Now, although this conclusion in itself may

not seem opposed to the theory of special creation, a most serious

difficulty is raised when it is taken in connexion with another fact of

an equally general kind. This is, that on every biological region we

encounter chains of allied species constituting allied genera, families,

and so on; while we scarcely ever meet with allied species in different

biological regions, notwithstanding that their climates may be similar,

and, consequently, just as well suited to maintain some of the allied

species. Hence we must further conclude, if all species were separately

created, that in the work of creation some unaccountable regard was paid

to making areas of distribution correspond to degrees of structural

affinity. A great many species of the rat genus were created in the Old

World, and a great many species of another, though allied, genus were

created in the New World: yet no reason can be assigned why no one

species of the Old World series should not just as well have been

deposited in the New World, and _vice versa_. On the other hand, the

theory of evolution may claim as direct evidence in its support all the

innumerable cases such as these--cases, indeed, so innumerable that, as

Mr. Wallace remarks, it may be taken as a law of nature that "every

species has come into existence coincident both in space and time with a

pre-existing and closely allied species." A general law which, while in

itself most strongly suggestive of evolution, is surely impossible to

reconcile with any reasonable theory of special creation. Furthermore,

this law extends backwards through all geological time, with the result

that the extinct species which now occur only as fossils on any given

geological area, resemble the species still living upon that area, as we

should expect that they must, if the former were the natural progenitors

of the latter. On the other hand, if they were not the natural

progenitors, but all the species, both living and extinct, were the

supernatural and therefore independent creations which the rival theory

would suppose, then no reason can be given why the extinct species

should thus resemble the living--any more than why the living species

should resemble one another. For, as we have seen, there are almost

always many other habitats on other parts of the globe, where any

members of any given group of species might equally well have been

deposited; and this, of course, applies to geological no less than to

historical time. Yet throughout all time we meet with this most

suggestive correlation between continuity of a geographical area and

structural affinity between the forms of life which have lived, or are

still living, upon that area.

Similarly, we find the further, and no less suggestive, correlation

between the birth of new species and the immediate pre-existence of

closely allied species on the same area--or, at most, on closely

contiguous areas.

Where a continuous area has long been circumscribed by barriers of any

kind, which prevent the animals from wandering beyond it, then we find

that all the species, both extinct and living, constitute more or less a

world of their own; while, on the other hand, where the animals are free

to migrate from one area to another, the course of their migrations is

marked by the origination of new species springing up _en route_, and

serving to connect the older, or metropolitan, forms with the younger,

or colonising, forms in the way of a graduated series. This principle,

however, admits of being traced only in certain cases of species

belonging to the same genus, of genera belonging to the same family, or,

at most, of families belonging to the same order. In other words, the

more general the structural affinity, the more general is the

geographical extension--as we should expect to be the case on the theory

of descent with branching modifications, seeing that the larger, the

older, and the more diverse the group of organisms compared, the greater

must be their chances of dispersal.

These general considerations led us to contemplate more in detail the

correlation between structural affinity and barriers to free migration.

Such barriers, of course, differ in the cases of different organisms.

Marine organisms are stopped by land, unsuitable temperature, or

unsuitable depths; fresh-water organisms by sea and by mountain-chains;

terrestrial organisms chiefly by water. Now it is a matter of fact

which admits of no dispute, that in each of these cases we meet with a

direct correlation between the kind of barrier and the kind of organisms

whose structural affinities are affected thereby. Where we have to do

with marine organisms, barriers such as the Isthmus of Panama and the

varying depth of the Western Pacific determine three very distinct

faunas, ranging north and south in closely parallel lines, and under

corresponding climates. Where we have to do with fresh-water organisms,

we find that a mountain-chain only a few miles wide has more influence

in determining differences of organic type on either side of it than is

exercised by even thousands of miles of a continuous land-area, if this

be uninterrupted by any mountains high enough to prevent water-fowl,

whirlwinds, &c., from dispersing the ova. Again, where we have to do

with terrestrial organisms, the most effectual barriers are wide reaches

of ocean; and, accordingly, we find that these exercise an enormous

influence on the modification of terrestrial types. Moreover, we find

that the _more_ terrestrial an organism, or the _greater_ the difficulty

it has in traversing a wide reach of ocean, the _greater_ is the

modifying influence of such a barrier upon that type. In oceanic

islands, for example, many of the plants and aquatic birds usually

belong to the same species as those which occur on the nearest

mainlands, and where there are any specific differences, these but

rarely run up to generic differences. But the land-birds, insects, and

reptiles which are found on such islands are nearly always specifically,

and very often generically, distinct from those on the nearest

mainland--although invariably allied with sufficient closeness to leave

no manner of doubt as to their affinities with the fauna of that

mainland. Lastly, no amphibians and no mammals (except bats) are ever

found on any oceanic islands. Yet, as we have seen, on the theory of

special creation, these islands must all be taken to have been the

theatres of the most extraordinary creative activity, so that on only

three of them we found no less than 1258 unique species, whereof 657

were unique species of land animals, to be set against one single

species known to occur elsewhere. Nevertheless, notwithstanding this

prodigious expenditure of creative energy in the case of land-birds,

land-shells, insects, and reptiles, no single new amphibian, or no

single new mammal, has been created on any single oceanic island, if we

except the only kind of mammal that is able to fly, and the ancestors of

which, like those of the land-birds and insects, might therefore have

reached the islands ages ago. Moreover, with regard to mammals, even in

cases where allied forms occur on either side of a sea-channel, it is

found to be a general rule that if the channel is shallow, the species

on either side of it are much more closely related than if it be

deep--and this irrespective of its width. Therefore we can only

conclude, in the words of Darwin--"As the amount of modification which

animals of all kinds undergo partly depends on lapse of time, and as the

islands which are separated from each other or from the mainland by

shallow channels are more likely to have been continuously united within

a recent period than islands separated by deeper channels, we can

understand how it is that a relation exists between the depth of the sea

separating two mammalian faunas, and the degree of their affinity--a

relation which is quite inexplicable on the theory of independent acts

of creation."

* * * * *

Looking to all these general principles of geographical distribution,

and remembering the sundry points of smaller detail relating to oceanic

islands which I will not wait to recapitulate, to my mind it seems that

there is no escape from the following conclusion, with which I will

bring my brief epitome of the evidence to a close. The conclusion to

which, I submit, all the evidence leads is, that if the doctrine of

special creation is taken to be true, then it must be further taken that

the one and only principle which has been consistently followed in the

geographical deposition of species, is that of so depositing them as to

make it everywhere appear that they were not thus deposited at all, but

came into existence where they now occur by way of genetic descent with

perpetual migration and correlative modification. On no other principle,

so far as I can see, would it be possible to account for the fact that

"every species has come into existence coincident both in space and time

with a pre-existing and closely allied species," together with the

carefully graduated regard to physical barriers which the Creator must

have displayed while depositing his newly formed species on either sides

of them--everywhere making _degrees_ of structural affinity correspond

to _degrees_ of geographical continuity, and _degrees_ of structural

difference correspond to _degrees_ of geographical separation, whether

by mountain-chains in the case of fresh-water faunas, by land and by

deep sea in the case of marine faunas, or by reaches of ocean in the

case of terrestrial faunas--stocking oceanic islands with an enormous

profusion of peculiar species all allied to those on the nearest

mainlands, yet everywhere avoiding the creation upon them of any

amphibian or mammal, except an occasional bat. We are familiar with the

doctrine that God is a God who hideth himself; here, however, it seems

to me, we should have but a thinly-veiled insinuation, not merely that

in his works he is hidden, but that in these works he is untrue. Than

which I cannot conceive a stronger condemnation of the theory which it

has been my object fairly to represent and dispassionately to

criticise.

SECTION II

_SELECTION_

CHAPTER VII.

THE THEORY OF NATURAL SELECTION.

Thus far we have been considering the main evidences of organic

evolution considered as a fact. We now enter a new field, namely, the

evidences which thus far have been brought to light touching the causes

of organic evolution considered as a process.

As was pointed out in the opening chapter, this is obviously the

methodical course to follow: we must have some reasonable assurance that

a fact is a fact before we endeavour to explain it. Nevertheless, it is

not necessary that we should actually demonstrate a fact to be a fact

before we endeavour to explain it. Even if we have but a reasonable

presumption as to its probability, we may find it well worth while to

consider its explanation; for by so doing we may obtain additional

evidence of the fact itself. And this because, if it really is a fact,

and if we hit upon the right explanation of it, by proving the

explanation probable, we may thereby greatly increase our evidence of

the fact. In the very case before us, for example, the evidence of

evolution as a fact has from the first been largely derived from testing

Darwin's theory concerning its method. It was this theoretical

explanation of its method which first set him seriously to enquire into

the evidences of evolution as a fact; and ever since he published his

results, the evidences which he adduced in favour of natural selection

as a method have constituted some of the strongest reasons which

scientific men have felt for accepting evolution as a fact. Of course

the evidence in favour of this fact has gone on steadily growing, quite

independently of the assistance which was thus so largely lent to it by

the distinctively Darwinian theory of its method; and, indeed, so much

has this been the case, that in the present treatise we have been able

to consider such direct evidence of the fact itself, without any

reference at all to the indirect or accessory evidence which is derived

from that of natural selection as a method. From which it follows that

in most of what I am about to say in subsequent chapters on the

evidences of natural selection as a method, there will be furnished a

large addition to the evidences which have already been detailed of

evolution as a fact. But, as a matter of systematic treatment, I have

thought it desirable to keep these two branches of our subject separate.

Which means that I have made the evidences of evolution as a fact to

stand independently on their own feet--feet which in my opinion are

amply strong enough to bear any weight of adverse criticism that can be

placed upon them.

Our position, then, is this. On the foundation of the previous chapters,

I will henceforth assume that we all accept organic evolution as a fact,

without requiring any of the accessory evidence which is gained by

independent proof of natural selection as a method. But in making this

assumption--namely, that we are all now firmly persuaded of the fact of

evolution--I do not imagine that such is really the case. I make the

assumption for the purposes of systematic exposition, and in order that

different parts of the subject may be kept distinct. I confess it does

appear to me remarkable that there should still be a doubt in any

educated mind touching the general fact of evolution; while it becomes

to me unaccountable that such should be the case with a few still living

men of science, who cannot be accused of being ignorant of the evidences

which have now been accumulated. But in whatever measure we may

severally have been convinced--or remained unconvinced--on this matter,

for the purposes of exposition I must hereafter assume that we are all

agreed to the extent of regarding the process of evolution as, at least,

sufficiently probable to justify enquiry touching its causes on

supposition of its truth.

Now, the causes of evolution have been set forth in a variety of

different hypotheses, only the chief of which need be mentioned here.

Historically speaking the first of these was that which was put forward

by Erasmus Darwin, Lamarck, and Herbert Spencer. It consists in putting

together the following facts and inferences.

We know that, in the lifetime of the individual, increased use of

structures leads to an increase of their functional efficiency; while,

on the other hand, disuse leads to atrophy. The arms of a blacksmith,

and the legs of a mountaineer, are familiar illustrations of the first

principle: our hospital wards are full of illustrations of the second.

Again, we know that the characters of parents are transmitted to their

progeny by means of heredity. Now the hypothesis in question consists

in supposing that if any particular organs in a species are habitually

used for performing any particular action, they must undergo a

structural improvement which would more and more adapt them to the

performance of that action; for in each generation constant use would

better and better adapt the structures to the discharge of their

functions, and they would then be bequeathed to the next generation in

this their improved form by heredity. So that, for instance, if there

had been a thousand generations of blacksmiths, we might expect the sons

of the last of them to inherit unusually strong arms, even if these

young men had themselves taken to some other trade not requiring any

special use of their arms. Similarly, if there had been a thousand

generations of men who used their arms but slightly, we should expect

their descendants to show but a puny development of the upper

extremities. Now let us apply all this to the animal kingdom in general.

The giraffe, for instance, is a ruminant whose entire frame has been

adapted to support an enormously long neck, which is of use to the

animal in reaching the foliage of trees. The ancestors of the giraffe,

having had ordinary necks, were supposed by Lamarck to have gradually

increased the length of them, through many successive generations, by

constantly stretching to reach high foliage; and he further supposed

that, when the neck became so long as to require for its support special

changes in the general form of the animal as a whole, these special

changes would have brought about the dwindling of other parts from which

so much activity was no longer required--the general result being that

the whole organization of the animal became more and more adapted to

browsing on high foliage. And so in the cases of other animals, Lamarck

believed that the adaptation of their forms to their habits could be

explained by this simple hypothesis that the habits created the forms,

through the effects of use and disuse, coupled with heredity.