Darwin and Descent 181 
it is not so obvious why the change should have been made 
at all, nor why the one “ my theory ” should have been 
taken and the other left, but I will return to this question. 
Again, Mr. Darwin writes :-— 
“ Although we must be extremely cautious in concluding 
that any organ could not possibly have been produced by 
small successive transitional gradations, yet, undoubtedly 
grave cases of difficulty occur, some of which will be dis- 
cussed in my future work ” (p. 192). 
This, as usual, implies descent with modification to be 
the theory that Mr. Darwin is trying to make good. 
Again :— 
“T have been astonished how rarely an organ can be 
named towards which no transitional variety is known to 
lead. . . . Why, on the theory of creation, should this be so ? 
. . - Why should not nature have taken a leap from struc- 
ture to structure? On the theory of natural selection we 
can clearly understand why she should not; for natural 
selection can act only by taking advantage of slight succes- 
sive variations; she can never take a leap, but must 
advance by the slowest and shortest steps ’’ (p. 194). 
Here “‘ the theory of natural selection ” is opposed to 
“the theory of creation ;” we took it, therefore, to be 
another way of saying ‘‘ the theory of descent with modifi- 
cation.” 
Again :— 
“We have in this chapter discussed some of the difficul- 
ties and objections which may be urged against my theory. 
Many of them are very grave, but I think that in the dis- 
cussion light has been thrown on several facts which, 
on the theory of independent acts of creation, are utterly 
obscure ”’ (p. 203). 
Here we have, on the one hand, “my theory,” on the 
other, ‘‘independent acts of creation.’”’ The natural 
antithesis to independent acts of creation is descent, and 
we assumed with reason that Mr. Darwin was claiming 
