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 Zhe 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 vagenalis 
and veeveszz, and from Phastanus 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. cygnozdes), 
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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