Genesis of Species
Another instance which may be cited is the asymmetrical condition of the heads of the flat-fishes (Pleuronectidae), such as the sole, the flounder, the brill, the turbot, &c. In all these fishes the two eyes, which in the young are situated as usual one on each side, come to be placed, in the adult, both on the same side of the head. If this condition had appeared at once, if in the hypothetically fortunate common ancestor of these fishes an eye had suddenly become thus transferred, then the perpetuation of such a transformation by the action of “Natural Selection” is conceivable enough. Such sudden changes, however, are not those favoured by the Darwinian theory, and indeed the accidental occurrence of such a spontaneous transformation is hardly conceivable. But if this is not so, if the transit was gradual, then how such transit of one eye a minute fraction of the journey towards the other side of the head could benefit the individual is indeed far from clear. It seems, even, that such an incipient transformation must rather have been injurious. Another point with regard to these flat-fishes is that they appear to be in all probability of recent origin—i.e. geologically speaking. There is, of course, no great stress to be laid on the mere absence of their remains from the secondary strata, nevertheless that absence is noteworthy, seeing that existing fish families, e.g. sharks (Squalidae), have been found abundantly even down so far as the carboniferous rocks, and traces of them in the Upper Silurian.
Another difficulty seems to be the first formation of the limbs of the higher animals. The lowest Vertebrata are perfectly limbless, and if, as most Darwinians would probably assume, the primeval vertebrate creature was also apodal, how are the preservation and development of the first rudiments of limbs to be accounted for—such rudiments being, on the hypothesis in question, infinitesimal and functionless?
In reply to this it has been suggested that a mere flattening of the end of the body has been useful, such, e.g., as we see in sea-snakes, which may be the rudiment of a tail formed strictly to aid in swimming. Also that a mere roughness of the skin might be useful to a swimming animal by holding the water better, that thus minute processes might be selected and preserved, and that, in the same way, these might be gradually increased into limbs. But it is, to say the least, very questionable whether a roughness of the skin, or minute processes, would be useful to a swimming animal; the motion of which they would as much impede as aid, unless they were at once capable of a suitable and appropriate action, which is against the hypothesis. Again, the change from mere indefinite and accidental processes to two regular pairs of symmetrical limbs, as the result of merely fortuitous, favouring variations, is a step the feasibility of which hardly commends itself to the reason, seeing the very different positions assumed by the ventral fins in different fishes. If the above suggestion made in opposition to the views here asserted be true, then the general constancy of position of the limbs of vertebrata may be considered as due to the position assumed by the primitive rugosities from which those limbs were generated. Clearly only two pairs of rugosities were so preserved and developed, and all limbs (on this view) are descendants of the same two pairs, as all have so similar a fundamental structure. Yet we find in many fishes the pair of fins, which correspond to the hinder limbs of other animals, placed so far forwards as to be either on the same level with, or actually in front of, the normally anterior pair of limbs; and such fishes are from this circumstance called “thoracic,” or “jugular” fishes respectively, as the weaver fishes and the cod. This is a wonderful contrast to the fixity of position of vertebrate limbs generally. If then such a change can have taken place in the comparatively short time occupied by the evolution of these special fish forms, we might certainly expect other and far more bizarre structures would (did not some law forbid) have been developed, from other rugosities, in the manifold exigencies of the multitudinous organisms which must (on the Darwinian hypothesis) have been gradually evolved during the enormous period intervening between the first appearance of vertebrate life and the present day.
Yet, with these exceptions, the position of the limbs is constant from the lower fishes up to man, there being always an anterior pectoral pair placed in front of a posterior or pelvic pair when both are present, and in no single instance are there more than these two pairs.
The development of whalebone (baleen) in the mouth of the whale is another difficulty. A whale’s mouth is furnished with very numerous horny plates, which hang down from the palate along each side of the mouth. They thus form two longitudinal series, each plate of which is placed transversely to the long axis of the body, and all are very close together. On depressing the lower lip the free outer edges of these plates come into view. Their inner edges are furnished with numerous coarse hair-like processes, consisting of some of the constituent fibres of the horny plates—which, as it were, fray out—and the mouth is thus lined, except below, by a network of countless fibres formed by the inner edges of the two series of plates. This network acts as a sort of sieve. When the whale feeds it takes into its mouth a great gulp of water, which it drives out again through the intervals of the horny plates of baleen, the fluid thus traversing the sieve of horny fibres, which retains the minute creatures on which these marine monsters subsist. Now it is obvious, that if this baleen had once attained such a size and development as to be at all useful, then its preservation and augmentation within serviceable limits, would be promoted by “Natural Selection” alone. But how to obtain the beginning of such useful development? There are indeed certain animals of exclusively aquatic habits (the dugong and manatee) which also possess more or less horn on the palate, and at first sight this might be taken as a mitigation of the difficulty; but it is not so, and the fact does not help us one step further along the road: for, in the first place, these latter animals differ so importantly in structure from whales and porpoises that they form an altogether distinct order, and cannot be thought to approximate to the whale’s progenitors. They are vegetarians, the whales feed on animals; the former never have the ribs articulated in the mode in which they are in some of the latter; the former have pectoral mammae, and the latter are provided with two inguinal mammary glands, and have the nostrils enlarged into blowers, which the former have not. The former thus constitute the order Sirenia, while the latter belong to the Cetacea. In the second place, the horny matter on the palates of the dugong and manatee has not, even initially, that “strainer” action, which is the characteristic function of the Cetacean “baleen.”
There is another very curious structure, the origin or the disappearance of which it seems impossible to account for on the hypothesis of minute indefinite variations. It is that of the mouth of the young kangaroo. In all mammals, as in ourselves, the air-passage from the lungs opens in the floor of the mouth behind the tongue, and in front of the opening of the gullet, so that each particle of food as it is swallowed passes over the opening, but is prevented from falling into it (and thus causing death from choking) by the action of a small cartilaginous shield (the epiglottis), which at the right moment bends back and protects the orifice. Now the kangaroo is born in such an exceedingly imperfect and undeveloped condition, that it is quite unable to suck. The mother therefore places the minute blind and naked young upon the nipple, and then injects milk into it by means of a special muscular envelope of the mammary gland. Did no special provision exist, the young one must infallibly be choked by the intrusion of the milk into the windpipe. But there is a special provision. The larynx is so elongated that it rises up into the posterior end of the nasal passage, and is thus enabled to give free entrance to the air for the lungs, while the milk passes harmlessly on each side of this elongated larynx, and so safely attains the gullet behind it.
Now, on the Darwinian hypothesis, either all mammals descended from marsupial progenitors, or else the marsupials, sprung from animals having in most respects the ordinary mammalian structure.
On the first alternative, how did “Natural Selection” remove this (at least perfectly innocent and harmless) structure in almost all other mammals, and, having done so, again reproduce it in precisely those forms which alone require it, namely, the Cetacea? That such a harmless structure need not be removed any Darwinian must confess, since a structure exists in both the crocodiles and gavials, which enables the former to breathe themselves while drowning the prey which they hold in their mouths. On Mr. Darwin’s hypothesis it could only have been developed where useful, therefore not in the gavials(!) which feed on fish, but which yet retain, as we might expect, this, in them superfluous but harmless formation.
On the second alternative, how did the elongated larynx itself arise, seeing that if its development lagged behind that of the maternal structure, the young primeval kangaroo must be choked: while without the injecting power in the mother, it must be starved? The struggle by the sole action of which such a form was developed must indeed have been severe!
The sea-urchins (Echinus) present us also with structures the origin of which it seems impossible to explain by the action of “Natural Selection” only. These lowly animals belong to that group of the star-fish class (Echinodermata), the species of which possess generally spheroidal bodies, built up of multitudinous calcareous plates, and constitute the order Echinoidea. They are also popularly known as sea-eggs. Utterly devoid of limbs, the locomotion of these creatures is effected by means of rows of small tubular suckers (which protrude through pores in the calcareous plates) and by moveable spines scattered over the body.
Besides these spines and suckers there are certain very peculiar structures, termed “Pedicellariae.” Each of these consists of a long slender stalk, ending in three short limbs—or rather jaws—the whole supported by a delicate internal skeleton. The three limbs (or jaws), which start from a common point at the end of the stalk, are in the constant habit of opening and closing together again with a snapping action, while the stalk itself sways about. The utility of these appendages is, even now, problematical. It may be that they remove from the surface of the animal’s body foreign substances which would be prejudicial to it, and which it cannot otherwise get rid of. But granting this, what would be the utility of the first rudimentary beginnings of such structures, and how could such incipient buddings have ever preserved the life of a single Echinus? It is true that on Darwinian principles the ancestral form from which the sea-urchin developed was different, and must not be conceived merely as an Echinus devoid of pedicellariae; but this makes the difficulty none the less. It is equally hard to imagine that the first rudiments of such structures could have been useful to any animal from which the Echinus might have been derived. Moreover, not even the sudden development of the snapping action could have been beneficial without the freely moveable stalk, nor could the latter have been efficient without the snapping jaws, yet no minute merely indefinite variations could simultaneously evolve these complex co-ordinations of structure; to deny this seems to do no less than to affirm a startling paradox.
Mr. Darwin explains the appearance of some structures, the utility of which is not apparent, by the existence of certain “laws of correlation.” By these he means that certain parts or organs of the body are so related to other organs or parts, that when the first are modified by the action of “Natural Selection,” or what not, the second are simultaneously affected, and increase proportionally or possibly so decrease. Examples of such are the hair and teeth in the naked Turkish dog, the general deafness of white cats with blue eyes, the relation between the presence of more or less down on young birds when first hatched, and the future colour of their plumage, with many others. But the idea that the modification of any internal or external part of the body of an Echinus carries with it the effect of producing elongated, flexible, triradiate, snapping processes, is, to say the very least, fully as obscure and mysterious as what is here contended for, viz. the efficient presence of an unknown internal natural law or laws conditioning the evolution of new specific forms from preceding ones, modified by the action of surrounding conditions, by “Natural Selection” and by other controlling influences.