SUMMARY OF THE EVIDENCE. 2O$ 



evidence, and contain no contradictions. Some of 

 them on the other hand, such as those considered 

 under the head of homology, are not due to lack of 

 evidence, but indicate that there are certain internal 

 principles of life which we do not understand, and 

 which are not covered by the heredity explanation, 

 at least in its ordinary sense. But in spite of these 

 obstacles the heredity explanation is the only one 

 which has stood the test of examination, and it 

 stands more firmly to-day than ever before. Finally 

 we have seen that the present distribution of 

 animals and plants is such as not only to be in 

 accordance with the descent theory, but in some 

 cases practically to prove the origin of species from 

 older ones. Specialists, in all of the branches of 

 study which we have considered, tell us that their 

 department of science considers the question of 

 evolution as no longer questionable. 



All of the evidence is indirect evidence, evolution 

 being simply an induction from the numerous facts. 

 Granting evolution, and it is plain that the present 

 condition of the world would be explanable by cer- 

 tain laws. The study of the present, which is all that 

 we have to study, shows that the condition of the 

 organic world is such as fully coincides with the 

 necessities of the theory. But this fact does not 

 prove the theory to be true. Proof is something 

 never found in the inductive sciences, and the evi- 

 dence collected here is of the same kind and nearly 

 as cogent as that brought forward for other induc- 

 tive conclusions. It is, for example, impossible to 

 prove that the fossils in our rocks have ever been 



