180 LIFE AND HABIT. 



to bar identity, and hence reproduction, by rendering 

 too severe an appeal to reason necessary for no crea- 

 ture can reproduce itself on the shallow foundation 

 which reason can alone give. Ordinarily, therefore, 

 the hybrid, or the spermatozoon or ovum, which it 

 may throw off (as the case may be), finds one single ex- 

 perience too small to give it the necessary faith, on the 

 strength of which even to try to reproduce itself. In 

 other cases the hybrid itself has failed to be developed ; 

 in others the hybrid, or first cross, is almost fertile ; in 

 others it is fertile, but produces depraved issue. The 

 result will vary with the capacities of the creatures 

 crossed, and the amount of conflict between their 

 several experiences. 



The above view would remove all difficulties out of 

 the way of evolution, in so far as the sterility of hybrids 

 is concerned. For it would thus appear that this steri- 

 lity has nothing to do with any supposed immutable 

 or fixed limits of species, but results simply from the 

 same principle which prevents old friends, no matter 

 how intimate in youth, from returning to their old in- 

 timacy after a lapse of years, during which they have 

 been subjected to widely different influences, inas- 

 much as they will each have contracted new habits, 

 and have got into new ways, which they do not like 

 now to alter. 



We should expect that our domesticated plants and 

 animals should vary most, inasmuch as these have been 

 subjected to changed conditions which would disturb 

 the memory, and, breaking the chain of recollection, 

 through failure of some one or other of the associated 



