DARWIN 347 



Darwin Wallace 



It has been shown in a for- (No cause of variation as- 



mer part of this work that such signed.) 



changes of external conditions Varieties do frequently oc- 

 would, from their acting upon cur spontaneously, 

 the reproductive system, prob- 

 ably cause the organisation All variations from the typi- 

 ... to become plastic. cal form have some definite 



Can it be doubted that . . . effect, however slight, on the 



any minute variation in struc- habits or capacities of the in- 



ture, habits, or instincts, adapt- dividuals. Abundance or rarity 



ing that individual better to the of a species is dependent on its 



new conditions, would tell upon more or less perfect adapta- 



its vigor and health? tion. If any species should pro- 



In the struggle it would have duce a variety having slightly 

 a better chance of surviving; increased powers of preserving 

 and those of the offspring who existence, that variety must in- 

 inherited the variation, be it evitably in time acquire a su- 

 ever so slight, would also have periority in numbers, 

 a better chance. 



Remarkable as this parallelism is, it is not com- 

 plete. The line of argument is the same, but the 

 point d'appui is different ; that is, Darwin had in 

 mind variations. Wallace had in mind varieties, 

 and there is a great biological difference between 

 the two concepts. Darwin dwells upon vari- 

 ations in single characters, as taken hold of 

 by selection; Wallace mentions variations, but 

 dwells upon full-formed varieties, as favorably 

 or unfavorably adapted. It is perfectly clear that 

 with Darwin the struggle is so intense that the 

 chance of survival of each individual turns upon 

 a single and even slight variation. With Wal- 

 lace, varieties are already presupposed by causes 

 which he does not discuss, a change in the envi- 

 ronment occurs, and those varieties which hap- 



