130 Rev. J. T. Gulick on the 



doctrine that without change in the environment there is no 

 change in the organism to the fruitless truism that witliout 

 some cause there is no change in the organism. An example 

 of Mr. Wallace's extending tlie meaning of the environment 

 so as to include the action of the members of a species on each 

 other is found on page 149. After mentioning several argu- 

 ments intended to show the impossibility that isolated portions 

 of a species should diverge while exposed to the same environ- 

 ment, he remarks, " It is impossible that the environment of 

 the isolated portion can be exactly like that of the bulk of the 

 species. It cannot be so physically, since no two separated 

 areas can be exactly alike in climate and soil ; and, even if 

 they are the same, the geographical features, size, contour, and 

 relation to winds, seas, and rivers would certainly differ. 

 Biologically the differences are sure to be considerable. The 

 isolated portion of a species will almost always be in a much 

 smaller area than that occupied by the species as a whole, hence 

 it is at once in a different position as regards its own hind.'''' 

 He then enumerates several differences in the biological 

 environment that are liable to occur ; but the point I wish 

 now to note is that he mentions as one of the differences in 

 the environment the " different position as regards its own 

 hind.^^ This is exactly the difference which, in so far as it is 

 the prevention of intercrossing and the consequent unification 

 of endowments and habits, constitutes isolation ; and unless he 

 is able to show that this difference is incapable of producing 

 any divergence, his contention is unsustained. But he here 

 yields the point at issue by mentioning this amongst the 

 effective differences. The only way to escape the force of his 

 concession is to claim, as he virtually does here, that isola- 

 tion, being the separation of the isolated fragment from the 

 influence of the original stock, is in itself a difference in 

 the environment. By taking this position, however, he 

 involves himself in another contradiction, for, if isolation is a 

 difference in the environment, why does he deny that it has a 

 direct influence in producing change in the organism ? 



Diversity oj Natural Selection during exposure to the 

 same Environment. 



Another discrepancy in Mr. Wallace's theory is that, while 

 he rightly assigns great importance to diversity of natural 

 selection arising from divergent habits in appropriating the 

 resources of the same environment, exhibited by different 

 sections of the same species occupying the same area^ he 

 nevertheless insists that the representatives of a species, iso- 



