Page:Darwinism by Alfred Wallace 1889.djvu/159

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a danger to the animal in passing rapidly through dense thickets. But Sir James Hector states, that the wapiti, in North America, throws back its head, thus placing the horns along the sides of the back, and is then enabled to rush through the thickest forest with great rapidity. The brow-antlers protect the face and eyes, while the widely spreading horns prevent injury to the neck or flanks. Thus an organ which was certainly developed as a sexual weapon, has been so guided and modified during its increase in size as to be of use in other ways. A similar use of the antlers of deer has been observed in India.[1]

The various classes of facts now referred to serve to show us that, in the case of the two higher groups—mammalia and birds—almost all the characters by which species are distinguished from each other are, or may be, adaptive. It is these two classes of animals which have been most studied and whose life-histories are supposed to be most fully known, yet even here the assertion of inutility, by an eminent naturalist, in the case of two important organs, has been sufficiently met by minute details either in the anatomy or in the habits of the groups referred to. Such a fact as this, together with the extensive series of characters already enumerated which have been of late years transferred from the "useless" to the "useful" class, should convince us, that the assertion of "inutility" in the case of any organ or peculiarity which is not a rudiment or a correlation, is not, and can never be, the statement of a fact, but merely an expression of our ignorance of its purpose or origin.[2]

  1. Nature, vol. xxxviii. p. 328.
  2. A very remarkable illustration of function in an apparently useless ornament is given by Semper. He says, "It is known that the skin of reptiles encloses the body with scales. These scales are distinguished by very various sculpturings, highly characteristic of the different species. Irrespective of their systematic significance they appear to be of no value in the life of the animal; indeed, they are viewed as ornamental without regard to the fact that they are microscopic and much too delicate to be visible to other animals of their own species. It might, therefore, seem hopeless to show the necessity for their existence on Darwinian principles, and to prove that they are physiologically active organs. Nevertheless, recent investigations on this point have furnished evidence that this is possible.

    "It is known that many reptiles, and above all the snakes, cast off the whole skin at once, whereas human beings do so by degrees. If by any accident they are prevented doing so, they infallibly die, because the old