190 
KEY. J. T. GULICK ON DIVERGENT EVOLUTION 
£ 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 different 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 Eittest ’ (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 Eittest ’ 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 difference of 
environment has been the occasion of different 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 Eittest ’ . . . . imply that there are variations 
that may be accumulated according to the differing demands of 
external conditions. What, then, is the effect 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 orgauism is through change in the environment, . . . 
