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Show 128 DARWINISM CHAP. variation is not essential. All animals in a state of nature are kept, by the constant struggle for existence and the survival of the fittest, in such a state of perfect health a11<l usually superabundant vigour, that in all ordinary circumstances they possess a surplus power in every important organ- a surplus only drawn upon in cases of the direst neces ity when their very existence is at stake. It follow. , therefore, thnt any additional power given to one of the component parts of nn organ mnst be useful- an increase, for example, either in the wing muscles or in the form or length of the wino- might crive some increased powers of flight; and thus alternate v:Lria.tionsin one generation in the muscles, in another generation in the wing itself-might be as effective in permanently improving the power. of flight as coincident variations at longer intervnl s. On either supposition, however, this objection appears to h;tve little weight if we talw into consideration the large amount of coincident variability that has been shown to exist. The Beginnings of Important Organs. We now come to an objection which has perhaps been more frequently urged than any other, and which Darwin himself felt to have much weight-the first beginnings of important organs, such, for example, as wings, eyes, mammary glands, and numerous other structures. It is uro-cd, th:tt it is almost impossible to conceive how the fir t rudiments of these could have been of any use, and, if not of use they conl(l not h_ave been preserved and further developed by natural selectiOn. Now~ the first remark to be made on objections of this na.t~re Is, that. t~ey are really outside the qnestion of the or1gm of all ex1stmg species from allied species not very far removed from them, which is all that Darwin undertook to p1·ove by means of his theory. Organs and structmes snch a. those above mentioned all date back to a very remote past, when the world and its inhabitants were both very different from what they arc now. To ask of a new theory that it shall reveal to us ~xactly what took place in remote geologica1 epochs, and how 1t took place, is unreasonable. The most th~t. sh~uld be asked is, that some probable or possible mode of ongmat1on should be pointed out in some at least of these VI DIFI•'ICUL'l'IEH AND OB.JECTIONS 129 difficult cases, and this Mr. Darwin has dono. One or two of these may be briefly given here, but the whole series should be carefully rend by any one who wi. hes to see how many curious facts and observations h:we been required in order to elucidate them ; whence we may conclude that further knowlodge wilr probably throw light on any difficulties that still remain.1 In the case of the mammary glands Mr. Darwin remarks that it is admitted that the ancestral mammals wore allied to the marsupials. Now in tho very earliest mammals, almost before they really deserved that name, the young may have been nourished by a fluid secreted by the interior surface of the marsupia1 sack, as is believed to be the case with the fish (Hippocampus) whoso eggs are hatched within a somewhat similar sack. This being tho case, those individuals which secreted a more nutritious fluid, and those whose young were able to obtain and swallow a more constant supply by suction, would be more likely to live and come to a healthy maturity, and would therefore be preserved by natmal.selection. In another case which has been adduced as one of special difficulty, a more complete explanation is given. Soles, turbots, and other flatfish are, as is well known, unsymmetrical. They live and move on their sides, the under side being usually differently coloured from that which is kept uppermost. Now tho eyes of these fish are curiously distorted in order that both eyes may bo on the upper side, where alone they would be of any use. It was objected by Mr. Mivart. that a sudden transformation of tho eye from one side to the other was inconceivable, while, if the transit were gradual the first stop could be of no use, since this would not remove the eye from the lower side. But, as Mr. Darwin shows by reference to the researches of Malm and others, the young of these fish are quite symmetrical, and during their growth exhibit to us the whole process of change. This begins by the fish (owing to the increasing depth of the body) being unable to maintain the vertical position, so that it falls on one side. It then twists tho lower eye as much as possible towards the upper side; and, the whole bony structure of the head being at 1 See Origin of Species, pp. 176-198. K |