128 CONDITIONS AFFECTING THE 



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 experi- 

 ments 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 opera- 

 tion of selective conditions, when you recollect as a matter 

 of fact, that for every species of animal or plant there 

 are fiftj' 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 opponents; 

 and that these have other animals preying upon them, 

 — that every plant has its indirect helpers in the birds 

 that scatter abroad its seed, and the animals that 

 manure it with their dung ; — I say, when these things 

 are considered, it seems impossible that any variation 



