110 OEGANIC EVOLUTION — THE FACTORS 



of the homs 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 favour- 

 ably in one and the same individual, and that they 

 continued' to vary favourably in a succession of indi- 

 viduals 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 homs 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 vertebrae of the neck 

 must be further developed ; and without the ligaments 

 that hold together these vertebrae and the muscles that 



