350 BIOLOGY 



vague way the idea of a gradual succession of higher and higher 

 forms of existence; and several other early philosophers specu- 

 lated concerning the origin of living things upon the earth accord- 

 ing to general processes of development. But these earlier 

 ideas were soon lost sight of and it was not until the seventeenth 

 century that any more modern ideas of the development of 

 animals from each other were advanced. During all of these 

 centuries, and indeed until about the middle of the nineteenth 

 century, so far as the subject was thought of at all, the view 

 generally accepted was that each different kind of animal and 

 plant was an independent creation. This view crystallized into 

 the special creation theory in the writings of John Ray in 1725, 

 and became the generally accepted view of all scientists. Dur- 

 ing the seventeenth and eighteenth centuries, however, several 

 philosophers expressed, in their writings, ideas approximating 

 the belief that living things do not remain forever constant, but 

 are ever going through the series of changes that we have al- 

 ready described as race divergence. Among those whose writ- 

 ings tended in this direction may be mentioned Kant, Goethe, 

 Leibnitz, Erasmus Darwin, and others. With the beginning of 

 the nineteenth century these conceptions began to take a more 

 definite shape. 



Lamarck. Lamarck was a French naturalist, living in about 

 the beginning of the nineteenth century, and was well versed in 

 botany and zoology. He formulated a clearly defined doctrine 

 of descent, and was the first of the modern scientists who had 

 any conception of the theory of evolution. Lamarck believed 

 that the fossils found in the rocks were the ancestors of 

 animals living to-day, and that the organisms of the present 

 world have been derived by descent from those that lived in 

 previous years. The changes that had taken place in their 

 structure he believed to have been slow and gradual, but contin- 

 uous, and produced by a variety of causes which he specified, 

 and which have received the name of Lamarckian factors. The 

 chief of these causes were the following: 



