THE THEORY OF ORGANIC EVOLUTION. 425 



from yet simpler forms, and so on backwards, till we 

 lose our clue in the unknown but doubtless momen- 

 tous vital events of pre-Cambrian ages, or, in other 

 words, in the thick mist of life's beginnings. 



HISTORY OF THE EVOLUTION-IDEA. 



" Though the general idea of organic evolution is 

 simple, it has been slowly evolved, gaining content 

 as research furnished fuller illustration, and gaining 

 clearness as criticism forced it to keep in touch with 

 facts. It has slowly developed from the stage of 

 suggestion to the stage of verification ; from being an 

 a priori anticipation it has become an interpretation 

 of nature ; and from being a modal interpretation it 

 is advancing to the rank of a causal theory." 4 



(1) In what we may call "the Greek Period," 

 there were many who more or less vaguely suggested 

 the evolution-idea, notably Empedocles (495-435 

 B.C.). Aristotle (384-322 B.C.) speaks clearly 

 of a gradual progression in nature from the inor- 

 ganic to the organic and from one grade of life to 

 another. f From Epicurus (341-270 B.C.), the 

 first poet of evolution, we pass after a long interval 

 to Lucretius (99-55 B.C.). 



(2) In the medireval period, though there was a 

 general arrest of enquiry, the light of the evolution- 

 idea did not wholly die. Bruno (1548-1600) at 

 least, who proclaimed that " the investigation of Na- 

 ture in the unbiased light of reason is our only 

 guide to truth," was in some degree an evolutionist. 



* See the writer's Science of Life, 1899 p. 213, where this 

 section forms the subject of a whole chapter " The Evolu- 

 tion of Evolution-Theory." 



f See E. Clodd, Pioneers of Evolution (1897); H. F. 03- 

 born, From the Greeks to Darwin (1894). 



