Page:George Archdall Reid 1896 The present evolution of man.djvu/122

110 of the horns would have been nugatory. With the larger horns it is as likely as not that weaker skull bones or structures in the neck, limbs, or trunk occurred. It is unreasonable to suppose that all the thousand co-ordinated structures did ever vary favourably in one and the same individual, and that they continued to vary favourably in a succession of individuals till the evolution of the moose was complete. On the contrary, it is only reasonable to suppose that some structures varied favourably, some unfavourably, and some varied not at all. A chain is only as strong as its weakest link. If with the larger horns there were associated co-ordinate structures in the head, neck, limbs, or trunk, weaker than the ordinary or only as strong as the ordinary, the larger horns would confer no advantage, but rather from their weight be a positive disadvantage. Consequently individuals with larger horns would not be the fittest, and therefore would not survive in increased numbers, and consequently there would be no evolution in horns. In Mr. Spencer's words—

"Other things equal, the blow given by a larger horn would be a blow given by a heavier mass moving at a smaller velocity; the momentum would be the same as before, and the area of contact with the body struck being somewhat increased, while the velocity was decreased, the injury would be somewhat less. That the horns may become better weapons, the whole apparatus which moves them must be so strengthened as to impress more force on them, and to bear the more violent reaction of the blows given. The bones of the skull on which the horns are seated must be thickened, otherwise they will break. To render the thickening of these bones advantageous the vertebræ of the neck must be further developed; and without the ligaments that hold together these vertebræ and the muscles that