34 EVOLUTION OF TO-DAY. 



The only really logical distinction ever given to 

 separate species and varieties is that of the sterility 

 of species when crossed, and the fertility of varie- 

 ties under the same conditions. It is said that 

 species cannot interbreed with each other, while all 

 varieties are perfectly fertile when crossed. This 

 gives a new understanding of species and varieties. 

 The difference between the two is not in any amount 

 of difference in bodily structure, but in affiliation. 

 All the varieties of a species are believed to have 

 descended from the same parent, and can conse- 

 quently breed with each other. Different species, 

 however, have not thus been connected, and can- 

 not interbreed. Sterility is thus regarded as a bar 

 set by the Creator to prevent the confusion which 

 would result from crossing. It is upon this distinc- 

 tion that those who believe in the stability of species 

 found most of their argument. If this be ad- 

 mitted as the definition of a species, the question 

 can at least be discussed, although open still to the 

 phantom chase above mentioned. Here is a limit 

 beyond which it is claimed variations cannot go. 

 It is pointed out that so far as our observations have 

 gone, no amount of variation has ever produced a 

 new species, if this be admitted as a distinction. In 

 no case has variation produced among domestic varie- 

 ties any degree of sterility. All of our breeds of 

 pigeons, as widely different as they are, can breed 

 freely with each other ; all of the numerous and 

 diverse breeds of dogs are perfectly fertile inter se ; 

 and so with domestic races in general. Indeed Dar- 

 win himself admits that he knows of no well- 



