EVOLUTION 169 



however, organic evolution was a pure speculation, with 

 no basis of scientific work. In other words, it was based 

 upon meditation rather than investigation, and was to 

 be regarded as a philosophy rather than a science. It 

 should be emphasized that the idea of evolution has 

 always been in the mind of men. 



During the latter part of this period certain facts be- 

 gan to be observed that made some thinking men con- 

 clude that evolution might be a fact, and not merely a 

 speculation. It will be helpful to note briefly, in his- 

 torical succession, the kinds of facts that set these men 

 to thinking, and that resulted in the second period in 

 the history of evolution, when it became a science. 



In classifying plants and animals, which was the 

 initial phase of biology, men rigidly defined the differ- 

 ent species, the thought being that the different kinds 

 had descended in unbroken succession "from the be- 

 ginning," whenever that may have been. When more 

 extensive observations were made in the field, numer- 

 ous intergrades began to be found. The species, as 

 defined, seemed to intergrade freely. In other words, 

 the pigeon-hole arrangement, with rigid partitions, did 

 not express the facts. It became evident that species 

 had been defined by man rather than by nature. Some 

 were distinct enough, but many intergraded. It ought 

 to be realized that a species is the conception of man, 

 and fluctuates just as do human opinions. Biologists 

 learned, therefore, that species are human inventions, 

 and intergrading suggested that one species might come 

 from another, the intergrades marking the trail. 



The next observations suggesting that evolution 



