INTRODUCTION 



diversity has become what we perceive it to be, we have to confess an 

 ignorance nearly total." — William Bateson, Problems of Genetics 

 (1913), p. 248. 



''The demonstration of evolution as a universal law of living 

 nature is the great intellectual achievement of the nineteenth century. 

 Evolution has outgrown the. rank of a theory, for it has won a place 

 in natural law beside Newton's law of gravitation, and in one sense 

 holds a still higher rank, because evolution is the universal master, 

 while gravitation is among its many agents. Nor is the law of evolu- 

 tion any longer to be associated 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 interpreting the work- . 

 ings 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 ihem. 

 In this open court of conjecture, of hypothesis, of more or less heated 

 controversy the names of Lamarck, of Darwin, of Weismann figure 

 prominently 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 Muta- 

 tion by De Vries. 



"In truth, from the period of the earlier stages of Greek thought 

 man has been eager to discover some natural cause of evolution, and 

 to abandon the idea of supernatural intervention 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 another: each of these waves of confidence 

 has ended in disappointment, until finally we have reached a stage 

 of very general scepticism. Thus the long period of evolution, experi- 

 ment, and reasoning which began with the French natural philosopher, 

 Buffon, one hundred and fifty years ago, ends in 1916 with the general 

 feeling that our search for causes, far from being near completion, has 

 only just begun. 



