428 NINETEENTH CENTURY. PT. in. 



There is only one difficulty. It is clear that the strong- 

 winged birds must not pair with the dark-winged birds, or 

 otherwise both peculiarities would come out in the young 

 birds, and the two kinds would no longer remain distinct. 

 And this is the one stumbling-block in the theory ; we 

 have never yet been able to trace out two varieties of an 

 animal which have become so different that they do not pair 

 together. You should fix this difficulty firmly in your mind, 

 because it is almost the only real one we shall meet with. 

 Mr. Darwin's answer to it is, that we have only watched 

 plants and animals for such a short time, and even then not 

 with this idea in our minds, so that we are not likely to 

 have found a case to help us. It has indeed been observed 

 that animals, if left free to choose, do often pair with those 

 which resemble themselves, and do in some cases show a 

 dislike to those that differ; still this is not proved to be 

 always the case, and it must be acknowledged to be a 

 difficulty. 



Selection of Animals by Man. But now setting this 

 aside, let us see what proof there is that animals vary, and that 

 they can be picked out, so that any peculiarity may become 

 stronger in each succeeding generation. The best instance is 

 in pigeons. All our pigeons come from the common wild 

 rock-pigeon ; and the way in which all our pouters, fan-tails, 

 barbs, and other pigeons have been produced, is by merely 

 picking out from the young ones those which had either large 

 crops, or wider tails, or longer beaks, and pairing them to- 

 gether, so that the young birds had these peculiarities still 

 more strongly. The same thing is true of our different kinds 

 of oxen, sheep, horses, and fowls ; so we see clearly that 

 different varieties can be produced by choosing out parti- 

 cular animals. Man does this quickly, because he only 



