The Making of Species 



only a rather common fact was elevated into a 

 law which had no exceptions." 



Thus the sterility of hybrids was a zoological 

 bogey which had to be demolished. The plan 

 of campaign adopted by Darwin and Wallace 

 was, firstly, to try to disprove the assertion that 

 the hybrids between different species are always 

 sterile, and secondly, to find a reason for the 

 alleged sterility of these hybrids. 



Darwin succeeded in obtaining some examples 

 of crosses between botanical species which 

 were said to be fertile. These he quotes in 

 chapter viii. of The Origin of Species. As 

 regards animals, he met with less success. 

 " Although," he writes, " I do not know of any 

 thoroughly well-authenticated cases of perfectly 

 fertile hybrid animals, I have some reason to 

 believe that the hybrids from Cervulus vaginalis 

 and reevesii, and from Phasianus colchicus and 

 P. torquatus and with P. versicolor are perfectly 

 fertile. There is no doubt that these three 

 pheasants, namely, the common, the true ring- 

 necked, and the Japan, intercross, and are 

 becoming blended together in the woods of 

 several parts of England. The hybrids from 

 the common and Chinese geese (A. cygnoides\ 

 species which are so different that they are 

 generally ranked in distinct genera, have often 

 been bred in this country with either pure 

 parent, and in one single instance they have 



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