XI PHENOMENA OF ORGANIC NATURE 453 
causes of the Present and of the Past conditions of 
ORGANIC NATURE, 
Such is the hypothesis as I understand it. Now 
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 con- 
ditions 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 lectures 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 diffi- 
cult inquiry :—Are the causes indicated compe- 
tent to give rise to the phenomena of organic 
nature? I suspect that this is indubitable to a 
certain extent. It is demonstrable, I think, as I 
have endeavoured to show you, that they are per- 
fectly competent to give rise to all the phenomena 
which are exhibited by RAcEsin nature. Further- 
more, 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 en- 
larged somewhat. Again, I think that the causes 
assumed are competent to account for most of the 
