THE COMING OF EVOLUTION 207 



or experimental evidence, and no satisfying suggestion 

 of a mode of operation. 



Nevertheless, through the eighteenth century and 

 increasingly in the first half of the nineteenth, one 

 naturalist after another ran counter to the prevailing 

 consensus of scientific opinion, and upheld some form 

 of evolutionary theory. First Buff on, who oscillated 

 between the orthodoxy of the Sorbonne and a belief 

 in " I'enchainement des toes," put forward a theory 

 of the direct modification of animals by external con- 

 ditions ; next Erasmus Darwin, poet, naturalist and 

 philosopher, caught a glimpse of the revelation which 

 was to be given in its fullness to his grandson, and 

 taught that, from " the metamorphoses of animals, as 

 from the tadpole to the frog, . . . the changes produced 

 by artificial cultivation, as in the breeds of horses, dogs, 

 and sheep, . . . the changes produced by conditions 

 of climate and season, ... the essential unity of 

 plan in all warm-blooded animals, we are led to con- 

 clude that they have been alike produced from a 

 similar living filament." 



But the first connected and logical theory is that 

 of Lamarck, who sought the cause of evolution in 

 the cumulative inheritance of modification induced 

 by the action of the environment. While, pace 

 Buffon, the effect of change in environment is small 

 on the structure of the individual, Lamarck held that, 

 if the necessary changes in habits became constant 

 and lasting, they would modify old organs, or, by the 

 need for new organs, call them into being. Thus the 

 ancestors of the giraffe acquired longer and longer 

 necks by continually stretching for leaves on trees 

 just beyond their reach, and the change of structure 



