556 THE EVOLUTION OP LIFE. 



forms show are profoundly significant. The unities of type 

 found under such different externals, are inexplicable except 

 as results of community of descent with non-community of 

 modification. Again, each organism analyzed apart, shows, 

 in the likenesses obscured by unlikenesses of its component 

 parts, a peculiarity which can be ascribed only to the formation 

 of a more heterogeneous organism out of a more homogeneous 

 one. And once more, the existence of rudimentary organs, 

 homologous with organs that are developed in allied animals 

 or plants, while it admits of no other rational interpretation, 

 is satisfactorily interpreted by the hypothesis of evolution. 



Last of the inductive evidences, came "the Arguments 

 from Distribution." While the facts of distribution in Space 

 are unaccountable as results of designed adaptation of organ- 

 isms to their habitats, they are accountable as results of the 

 competition of species, and the spread of the more fit into 

 the habitats of the less fit, followed by the changes which 

 new conditions induce. Though the facts of distribution in 

 Time are so fragmentary that no positive conclusion can be 

 drawn, yet all of them are reconcilable with the hypothesis 

 of evolution, and some of them yield it strong support: 

 especially the near relationship existing between the living 

 and extinct types in each great geographical area. 



Thus of these four groups, each furnished several argu- 

 ments which point to the same conclusion; and the conclu- 

 sion pointed to by the arguments of any one group, is that 

 pointed to by the arguments of every other group. This 

 coincidence of coincidences would give to the induction a 

 very high degree of probability, even were it not enforced by 

 deduction. But the conclusion deductively reached, is in 

 harmony with the inductive conclusion. 



§ 173. Passing from the evidence that evolution has taken 

 place, to the question — How has it taken place? we find in 

 known agencies and known processes, adequate causes of its 

 phenomena. 



