122 CONDITIONS AFFECTING THE 



globe, and extirpate or replace the other kinds. That 

 is what is meant by Natural Selection ; that is the 

 kind of argument by which it is perfectly demonstrable 

 that the conditions of existence may play exactly the 

 same part for natural varieties as man does for domesti- 

 cated varieties. No one doubts at all that particular 

 circumstances may be more favorable for one plant and 

 less so for another, and the moment you admit that, you 

 admit the selective power of nature. Now, although I 

 have been putting a hypothetical case, you must not 

 suppose that I have been reasoning hypothetically. 

 There are plenty of direct experiments which bear out 

 what we may call the theory of natural selection ; there 

 is extremely good authority for the statement that if you 

 take the seed of mixed varieties of wheat and sow it, 

 collecting the seed next year and sowing it again, at 

 length you will find that out of all your varieties, only 

 two or three have lived, or perhaps even only one. 

 There were one or two varieties which were best fitted 

 to get on, and they have killed out the other kinds in 

 just the same way and with just the same certainty as 

 if you had taken the trouble to remove them. As I 

 have already said, the operation of nature is exactly the 

 same as the artificial operation of man. 



But if this be true of that simple case, which I put 

 before you, where there is nothing but the rivalry of one 

 member of a species with others, what must be the 

 operation of selective conditions, when you recollect as 

 a matter of fact, that for every species of animal or 

 plant there are fifty or a hundred species which might 

 all, more or less, be comprehended in the same climate, 

 food, and station ; — that every plant has multitudinous 

 animals which prey upon it, and which are its direct 



