INDIRECT EQUILIBRATION. 403 



permanent -weakness in one of its ligaments ■will greatly 

 diminisli. tlie power of a limb, it will be seen that unless all 

 these many changes are simultaneously made, they may as 

 well be none of them made — or rather, they had better be 

 none of them made ; since, the enlargements of some parts, 

 by putting greater strains on connected parts, would render 

 Ihem relatively weaker if they remained xmenlarged. Thus, 

 then, to account by the hj'pothesis of natural selection, for such 

 a structure as that of the moose deer, or the extinct Irish elk, 

 we must suppose a spontaneous increase in the size of the 

 horns, to be accompanied by a spontaneous increase in each 

 of these numerous bones and muscles and ligaments directly 

 and indirectly implicated in the use of the horns. Can we 

 with any propriety do this ? I think not. It would be a 

 strong supposition that the vertebrae and muscles of the neck, 

 spontaneously enlarged at the same time as the horns. It 

 would be a still stronger supposition that the upper dorsal 

 vertebrae not only at the same time spontaneously became 

 more massive, but also spontaneously altered their pro- 

 portions in appropriate ways, by the development of their 

 immense neural spines. And it would be an assumption 

 still more straining our powers of belief, that along with 

 heavier horns there should spontaneously take place the re- 

 quired strengthenings of the scapular arch and the fore-legs. 

 Besides the multiplication of directly-cooperativf organs, 

 the multiplication of organs that do not cooperate, save in 

 the degree implied by their combination in the same organ- 

 ism, seems to me a further hindrance to the development of 

 special structures by natural selection alone. Where the Ufa 

 is comparatively simple, or where surrounding circumstances 

 render some one function supremely important, the survival 

 of the fittest may readily bring about the appropriate struc- 

 tural change, without any aid from the transmission of fimc- 

 tionaUy-acquired modifications. But in proportion as the 

 life grows complex — in proportion as a healthy existence 

 cuimot be secured by a large endowment of some one power. 



