138 THE STORY OF THE LIVING MACHINE. 



tory has been simply that of perfecting the early 

 machines rather than the production of new types. 



Evidence for this History. As just outlined, we 

 see that the living machines have been gradually 

 brought into their present condition by a process 

 which has been called organic evolution. But we 

 must pause for a moment to ask what is our evi- 

 dence that such has been the history of the living 

 machine. The whole possibility of understand- 

 ing living nature depends upon our accepting 

 this history and rinding an explanation of it. At 

 the outset we have the question of fact, and we 

 must notice the grounds upon which we stand in 

 assuming this history to be as outlined. 



This problem is the one which has occupied 

 such a prominent place in the scientific world 

 during the last forty years, and which has contrib- 

 uted so largely toward making modern biology 

 such a different subject from the earlier studies 

 of natural history. It is simply the evidence 

 for organic evolution, or the theory of descent. 

 The subject has for forty years been thoroughly 

 sifted and tested by every conceivable sort of test. 

 As a result of the interest in the question there 

 has been disclosed an immense mass of evidence, 

 relevant and irrelevant. As the evidence has ac- 

 cumulated it has become more and more evident 

 that the evolution theory must be recognized as 

 the only one which is in accord with the facts, and 

 the outcome has been a practical unanimity among 

 thinkers that the theory of descent must be the 

 foundation of our further study. The evidence 

 which has forced this conclusion upon scientists 

 we must stop for a moment to consider, since 

 it bears very directly upon the subject we are 

 studying. 



