Evolution of Evolution-Theory. 219 



George Louis Leclerc Buffon (1707-1788) was the 

 first of the great pioneers of modern evolution doctrine. 

 Reversing Cuvier's change of opinion, he 

 passed from an early belief in the fixity of SrModrn 

 species to an extreme theory of their muta- 

 bility (1761-1766), from which he afterwards 

 in some measure reacted. Although frequently quite 

 explicit as to the general idea of evolution, he continu- 

 ally recoiled from his own conclusions, and contradicted 

 himself to avoid contradicting the Scriptures. But it 

 is hard to tell whether this was an expression of ironical 

 humour, or an attempt to temporize between science 

 and orthodoxy, or due to a perception of the difficulty 

 of the problem. His conception of descent was im- 

 perfect in so far as he adhered to the linear series 

 expounded by Bonnet, nor did he combine his various 

 aetiological suggestions into a consistent theory; but he 

 is entitled to a very high place in the history, since he 

 asked many new questions if he did not answer them, 

 and because of his anticipation of many important ideas, 

 such as pangenesis, the struggle for existence, artificial 

 and natural selection, and geographical isolation. His 

 most significant contribution to aetiology was his theory 

 that the direct action of the environment produced 

 structural changes which were conserved by here- 

 dity. 



Erasmus Darwin (1731-1802), grandfather of Charles 

 Darwin, expounded in prose and verse a theory of the 

 gradual and natural development of organisms from 

 spontaneously generated primordial forms of great sim- 

 plicity, endowed with an irritability and excitability 

 which made evolution possible. He extended the con- 

 ception of the struggle for existence to plants as well as 

 animals, but does not seem to have perceived the vital 

 connection between struggle and progress. Although 

 much influenced by BufFon, he held a different causal 

 theory, emphasizing not the direct influence of the 

 environment, but its indirect effect in evoking functional 

 reactions, which in turn produced modifications. "All 

 animals", he says, "undergo transformations which are 

 in part produced by their own exertions, in response to 



