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let us see how it will stand the various tests which I laid 

 down just now. In the first place, do these supposed 

 causes of the phenomena exist in nature ? Is it the 

 fact that in nature these properties of organic matter 

 ■ — atavism and variability — and those phenomena which 

 we have called the conditions of existence, — is it true 

 that they exist ? Well, of course, if they do not exist, 

 all that I have told you in the last three or four lec- 

 tures must be incorrect, because I have been attempting 

 to prove that they do exist, and I take it that there is 

 abundant evidence that they do exist ; so far, therefore, 

 the hypothesis does not break down. 



But in the next place comes a much more difficult 

 inquiry : — Are the causes indicated competent to give 

 rise to the phenomena of organic nature ? I suspect 

 that this is indubitable to a certain extent. It is de- 

 monstrable, I think, as I have endeavoured to show 

 you, that they are perfectly competent to give rise to all 

 the phenomena which are exhibited by Races in nature. 

 Furthermore, I believe that they are quite competent 

 to account for all that we may call purely structural 

 phenomena which are exhibited by Species in nature. 

 On that point also I have already enlarged somewhat. 

 Again, I think that the causes assumed are competent 

 to account for most of the physiological characteristics 

 of species, and I not only think that they are competent 

 to account for them, but I think that they account for 

 many things which otherwise remain wholly unaccount- 

 able and inexplicable, and I may say incomprehensible. 

 For a full exposition of the grounds on which this con- 

 viction is based, I must refer you to Mr. Darwin's 

 work ; all that I can do now is to illustrate what I have 

 said by two or three cases taken almost at random. 



