CHAPTER VII 



THE BIOLOGICAL SCIENCE OF THE MODERN 



PERIOD: THE THEORY OF ORGANIC 



EVOLUTION 



THE Cell-Doctrine and the doctrine of Organic Evolution 

 are the two most fundamental generalizations thus far 

 established in biological science. It is difficult to say which 

 has been the more effective in unifying a wide range of 

 established facts. As we have seen the cell-theory is a key 

 to the structures and functions which are everywhere ob- 

 servable in animals and plants. Its significance in the his- 

 tory of living things is almost wholly by implication from 

 what exists in the present. The theory of organic evolu- 

 tion is primarily significant as an explanation of the past. 

 Whether we consider the one or the other the greater gener- 

 alization depends upon whether we are interested in the 

 immediate vital phenomena and their control by man, or 

 attracted by the philosophical aspects of biology. Cell 

 problems are problems of the present and of that part of the 

 future which will be important to the human race. The 

 problem of organic evolution is mainly a problem of the 

 historical origin of the animal and plant bodies around us. 

 The origin of the human species in comparatively recent 

 times and the beginnings of life upon our planet are two of its 

 most interesting aspects. 



But organic evolution is only an aspect of the Evolution 

 of the Cosmos. Evolutionary development has come to be 

 accepted as the most reasonable explanation for the origin 

 of what now exists. This is true, whether it be the bodies 

 of animals and plants, the surface of the earth, or solar 

 systems. Organic evolution is part of the cosmic evolution, 

 by which the universe has reached its present organization. 



155 



