COSMIC PHILOSOPHY 



phologically the carrier, the pouter, and the 

 tumbler may well be regarded as distinct species 

 artificially developed from a common wild stock ; 

 but so long as mutual infertility is held to be 

 the physiological test by which we are to dis- 

 tinguish between varieties and species, it may 

 be argued that, in spite of their great morpho- 

 logical differences, the carrier and the tumbler 

 are only varieties and not true species. And 

 going a step farther, it may be argued that until 

 the theory of natural selection has accounted 

 for the rise of infertility between races descended 

 from a common stock, it has not completely 

 performed the task of reconciling deduction with 

 observation. 



Against the derivation theory in general this 

 objection has no weight whatever. That races 

 originally fertile together should, after long 

 subjection to different sets of circumstances, be- 

 come infertile with one another, is a priori in 

 the highest degree probable, when we reflect 

 upon the extreme sensitiveness of the reproduc- 

 tive system to changes of habit in the organism 

 as a whole. When we remember that " the 

 constitution of many wild animals is so altered 

 by confinement that they will not breed even 

 with their own females," we need not be sur- 

 prised that the leopard and the lion, which dur- 

 ing many ages have had very different habits 

 of life, will not breed with each other. Nor 



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