276 THE EVOLUTION OF SEX. 



CHAPTER XXI. 

 THE REPRODUCTIVE FACTOR IN EVOLUTION. 



I. General History of Evolution.— The history of the doctrine 

 of evolution is essentially modern; for though the idea glimmered 

 before the minds of many ancient philosophers from Empedocles to 

 Lucretius, 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 distin- 

 guish, on the one hand, the gradual demonstration of the fact that 

 evoluti on is a mod al explanation of the origin of organisms; and, on 

 the other, the deeper problem of the real mechanism of the pro- 

 cess. The former, the empirical fact of evolution, may be said to 

 have been virtually demonstrated, soon after the middle of this 

 century, by the labors of Spencer, 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. 



Th e idea of evolutio n, 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 g eneral con ception with 

 diplomatic skill and powerful irony, b ut sought to elucidate the 

 wor king out of the pro cess. He ill ustrated the influenc e of new 

 condition s in evoking new functions; showed how these in turn 

 reacted upon the structure of the organism; a nd how, most direc tly 

 of all, altered climate, food, and other elements of the environment 

 wer e external factors in internal chang e, whether for progress or 

 for degeneration - 

 Contrasted with Buflfon in many ways, both in his mode of treat- 

 ment 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 humor and common-sense of a true Englishman, 

 and with a really living conception of Nature, he urged the general 

 conception of evolution, and .emphasized the organis m's inherent 

 power of self-improvement, the molding influence of new needs, 

 de sires, and exertions T a nd the indirect action of the environment in 

 evoking these. 



To Treviranus (writing in 1802-31) — a biologist too much 

 neglected both in his lifetime and since — organisms appeared almost 

 indefinitely plastic, especially however under the direct influence of 



