CHAP. IT.] INCIPIENT STRUCTURES. 27 



" Slight individual differences, however, suffice for the 

 work, and are probably the sole differences which are effec- 

 tive in the production of new species." And again, after 

 mentioning the frequent sudden appearances of domestic 

 varieties, he speaks of " the false belief as to the similarity 

 of natural species in this respect." * In his work on the 

 " Origin of Species," he also observes, " Natural Selection 

 acts only by the preservation and accumulation of small 

 inherited modifications." 2 And " Natural Selection, if it 

 be a true principle, will banish the belief ... of any 

 great and sudden modification in their structure." 3 Finally, 

 he adds, " If it could be demonstrated that any complex 

 organ existed, which could not possibly have been formed 

 by numerous, successive, slight modifications, rny theory 

 would absolutely break down." 4 



Now the conservation of minute variations in many 

 instances is, of course, plain and intelligible enough ; such, 

 e.g., as those which tend to promote the destructive 

 faculties of beasts of prey on the one hand, or to 

 facilitate the flight or concealment of the animals pursued 

 on the other ; provided always that these minute beginnings 

 are of such a kind as really to have a certain efficiency, 

 however small, in favour of the conservation of the in- 

 dividual possessing them ; and also provided that no un- 

 favourable peculiarity in any other direction accompanies 

 and neutralizes, in the struggle for life, the minute favour- 

 able variation. 



1 "Animals and Plants under Domestication," vol. ii. p. 414. 



2 "Origin of Species," 5th edit., 1869, p. 110. 



3 Ibid. p. 111. 



4 Ibid. p. 227. Even in his recently published work, Mr. Darwin 

 observes, " Slight fluctuating differences in the individual suffice for the 

 work of natural selection." See "Descent of Man," vol. ii. p. 387. 



