CHAPTER XLII 



EXPLANATIONS OF EVOLUTION 



THE following chapter indicates the successive appear- 

 ance of the great groups of plants, beginning with simple 

 algae and ending with complex seed plants. This is an 

 illustration of what is called organic evolution, which means 

 that the plants and animals of to-day are the modified 

 descendants of earlier forms. This theory of descent, as 

 organic evolution is often called, is now universally ac- 

 cepted by biologists, but they differ widely among them- 

 selves as to how the modifications have been brought 

 about. The theory of evolution is as old as our record of 

 human thought, and no man can be cited as its author. 

 The names that have been conspicuously associated with it 

 are the names of men who have tried to explain it. All 

 their explanations may prove to be inadequate, but still the 

 theory of evolution will remain to be explained. 



The attempted explanations of evolution have been 

 numerous, but four great epochs in the history of the theory 

 are recognized, each introduced by a new explanation 

 which changed the point of view. 



i. The first epoch was introduced in the last decade of 

 the eighteenth century when three men independently 

 proposed the same explanation of evolution. They were 

 Erasmus Darwin of England, St. Hilaire of France, and 

 Goethe in Germany. Their explanation was called the 



333 



