PREFACE ix 



agents. Nor is the law of evolution any longer to be associ- 

 ated with any single name, not even with that of Darwin, 

 who was its greatest exponent.^ It is natural that evolution 

 and Darwinism should be closely connected in many minds, 

 but we must keep clear the distinction that evolution is a law, 

 while Darwinism is merely one of the several ways of inter- 

 preting the workings of this law. 



In contrast to the unity of opinion on the law of evolution 

 is the wide diversity of opinion on the causes of evolution. 

 In fact, the causes of the evolution of life are as mysterious as 

 the law of evolution is certain. Some contend that we already 

 know the chief causes of evolution, others contend that we 

 know little or nothing of them. In this open court of con- 

 jecture, of hypothesis, of more or less heated controversy, the 

 great names of Lamarck, of Darwin, of Weismann figure promi- 

 nently as leaders of different schools of opinion; while there 

 are others, like myself,- who for various reasons belong to no 

 school, and are as agnostic about Lamarckism as they are 

 about Darwinism or Weismannism, or the more recent form 

 of Darwinism, termed Mutation by de Vries. 



In truth, from the period of the earliest stages of Greek 

 thought man has been eager to discover some natural cause of 

 evolution, and to abandon the idea of supernatural interven- 

 tion in the order of nature. Between the appearance of The 

 Origin of Species, in 1859, and the present time there have 

 been great waves of faith in one explanation and then in an- 

 other: each of these waves of confidence has ended in disap- 

 pointment, until finally we have reached a stage of very general 



1 See From the Greeks to Darwin (Macmillan & Co., 1894), by the present author, in 

 which the whole history of the evolution idea is traced from its first conception down to 

 the time of Darwin. 



* Osborn, H. F., "The Hereditary Mechanism and the Search for the Unknown Factors 

 of Evolution," The Amer. Naturalist, May, 1895, pp. 418-439. 



