FACTORS OF ORGANIC EVOLUTION 559 



ability to live independently, and are not so well equipped in 

 other ways as the Algae. Likewise through regressive evolution 

 the Bacteria are supposed to have originated from the Blue-green 

 Algae. 



Although evolution is most commonly considered in connection 

 with the past, its processes are still in operation and will continue 

 to be as long as matter can change. Its processes are so slow 

 that ordinarily centuries are required to produce perceptible 

 changes. In producing the forms of plants and animals that 

 are now in existence, some estimate that more than fifty million 

 years have been required. 



In this discussion we are concerned with the evolution of 

 organisms and chiefly with the evolution of plants, but evolution 

 is far broader than this. There is inorganic as well as organic 

 evolution. In books on evolution we find discussions upon the 

 evolution of matter, in which the idea is set forth that the earth, 

 moon, stars, and all of the bodies of the universe owe their present 

 form and features to the process of evolution. Books also treat 

 of the evolution of society, church, state, and of intellectual and 

 moral evolution. Thus evolution pertains to everything that is 

 undergoing transitions from one state of existence to another. 



Factors of Organic Evolution. Variations and heredity are 

 the chief factors of organic evolution. 



If organisms remained fixed in structure and function, the 

 origin of new forms from previously existing ones would be impos- 

 sible. All one celled organisms would have remained one celled 

 and constant in all of their features from generation to generation. 

 No multicellular organisms could have developed from them. But 

 the theory of evolution assumes that one celled organisms vary 

 so that from them multicellular organisms arise and these in turn 

 vary, giving rise to more multicellular and better organized forms. 

 Thus through variations occurring in every direction and affecting 

 every conceivable structure, forms differing from their ancestors 

 in all kinds of ways are constantly appearing. Of course, within 

 the period of one's life time, or even within the period of human 

 history, the effects of variations in producing new and distinct 

 types of plants and animals appear insignificant, but the numer- 

 ous centuries since life began are thought to afford enough time 

 for all the multitudinous forms of living beings to arise in this way. 



Accompanying variations there must be heredity, otherwise 



