CHAPTER XXI 



THE REPRODUCTIVE FACTOR IN EVOLUTION. 



§ I. Ge7ieral History of Evohitio7i. — The history of the doctrine 

 of evolution is essentially modern ; for though the idea glim- 

 mered before the minds of many ancient philosophers from 

 Empedocles to I>ucretius, it was not till the eighteenth century 

 that naturalists began seriously to apply the conception to the 

 problem of the origin of our fauna and flora. In thinking of 

 the history, it is necessary to distinguish, on the one hand, the 

 gradual demonstration of the fact that evolution is a modal 

 explanation of the origin of organisms, and, on the other, the 

 deeper problem of the real mechanism of the process. The 

 former, the empirical fact of evolution, may be said to have 

 been virtually demonstrated, soon after the middle of this 

 century, by the labours of Sj^encer, Darwin, Wallace, Haeckel, 

 and others; the latter— the real aetiology of organisms, the 

 "how" of the process — is still the subject of searching inquiry 

 and keen debate. 



The idea of evolution, for so many centuries a latent germ, 

 first took definite shape, so far as biology is concerned, in the 

 mind of Buffon (1749), who not only urged the general con- 

 ception with diplomatic skill and powerful irony, but sought to 

 elucidate the working out of the process. He illustrated the 

 influence of new conditions in evoking new functions ; showed 

 how these in turn reacted upon the structure of the organism ; 

 and how, most directly of all, altered climate, food, and other 

 elements of the environment, were external factors in internal 

 change, whether for progress or for degeneration. 



Contrasted with Buffon in many ways, both in his mode of 

 treatment and in his view of the factors, was Erasmus Darwin 

 (1794), the grandfather of the author of the "Origin of Species." 

 In rhyme and reason, with all the humour and common-sense 

 of a true Englishman, and with a really living conception of 

 nature, he urged the general conception of evolution, and 



