190 EEV. J. T. OTJLICK ON DIVEEaENT EYOLIJTION 



' Nature ' for July 18, 1872 ; the other, entitled " Diversity of 

 Evolution under one Set of External Conditions," after being read 

 before the British Association for the Advancement of Science in 

 August 1872, was, through the kindness of Mr. Alfred Wallace, 

 brought before the Linnean Society, and was finally published in 

 the Linnean Society's Journal, Zoology, vol. xi. pp. 496-505. 



In the former paper I used the following words in calling 

 attention to the impossibility of explaining the origin and distri- 

 bution of these forms by Natural Selection. " "Whether we call 

 the diflferent forms species or varieties, the same questions are 

 suggested as to how they have arisen and as to how they have 

 been distributed in their several localities. In answering these 

 questions, we find it difficult to point to any of those active 

 causes of accumulated variation, classed by Darwin as Natural 



Selection There is no reason to doubt that some varieties 



less fitted to survive have disappeared; but it does not follow 

 that the ' Survival of the Fittest ' (those best fitted when com- 

 pared with those dying prematurely, but equally fitted when 

 compared with each other) is the determining cause which has 

 led to these three species being separated from each other in 

 adjoining valleys. The ^Survival of the Fittest ' still leaves a 

 problem concerning the distribution of those equally fitted. It 

 cannot be shown that the ' Survival of the Fittest ' is at variance 

 with the survival, under one set of external circumstances, 

 of varieties differing more and more widely from each other 

 in each successive generation. The case of the species under 

 consideration does not seem to be one in which diff'erence of 

 environment has been the occasion of diff'erent forms being 

 preserved in the different localities. It is rather one in which 

 varieties resulting from some other cause, though equally fitted 

 to survive in each of the localities, have been distributed accord- 

 ing to their affinities in separate localities." 



In the latter paper I raised the following questions con- 

 cerning Natural Selection. " The terms ' Natural Selection ' and 

 ' Survival of the Fittest ' . . . . imply that there are variations 

 that may be accumulated according to the diff"ering demands of 

 external conditions. What, then, is the eff'ect of these variations 

 when the external conditions remain the same ? Or, can it be 

 shown that there is no change in organisms that is not the result 

 of change in external conditions ? Again, if the initiation of 

 change in the organism is through change in the environment, . . . 



