THE DAWN OF THE EVOLUTIONARY PERIOD. 227 



almost all the weight which might otherwise have been 

 attached to it. Goethe, likewise, arrived at the idea of the 

 mutability of species, but he only expressed his views 

 ' aphoristically,' and they met with no acceptance from the 

 world at large. Erasmus Darwin, however, firmly grasped 

 and clearly laid down many of the principles which are 

 involved in the modern theories of the evolution of 

 species. His views on this question are mostly contained 

 in the section of the 'ZoonormV which deals with the 

 function of reproduction ; but most of the ideas to which 

 he had been led had been more or less explicitly 

 propounded in the previously published 'Loves of the 

 Plants.' 



In the first place, he not only recognised the natural 

 variations which present themselves in different individuals 

 of a species, but also those which are the result of 

 artificial or accidental cultivation. Thus, he pointed out 

 the numerous structural peculiarities which have been 

 induced in special breeds of such animals as horses and 

 dogs, which have been long exercised for particular 

 purposes; and he drew attention to the fact that some 

 of our domestic animals had undergone changes so great 

 that it was now no longer possible to determine with 

 certainty from what wild species they had their origin. 

 He also indicated that variations, sometimes of con- 

 siderable importance, such as the presence of an additional 

 digit, or the want of the tail, might occur, and might 

 become permanent. 



In the second place, he clearly recognised the principle 

 of heredity; and he pointed out that not only might 

 the structural peculiarities of individual animals be trans- 



