JENNINGS: CHANGES IN HEREDITARY CHARACTERS 299 



that evolution has occurred by loss and disintegration. Daven- 

 port combines this idea with the theory that these disintegrating 

 variations follow a definite course, predetermined in large 

 measure by the constitution of the disintegrating material. 



There are two points worth consideration in dealing with this 

 theory. The first is one of fact; although it is true that many 

 of the so-called mutations appear to be cases of loss and disinte- 

 gration,, yet there is no indication that this is the case in such 

 effects of selection as have been described by Castle and myself; 

 variations are not limited to any particular direction. Secondly, 

 it appears to me that this conclusion — that because the variations 

 we see are cases of loss and disintegration, therefore evolution 

 must have occurred by loss and disintegration — it appears to 

 me, I say, that this conclusion involves an error in logic, which 

 makes it unworthy of serious consideration. The syllogism which 

 it involves seems something as follows : 



1. Major premise. Evolution has occurred by progress from 

 the visibly less differentiated in structure to the visibly more 

 differentiated in structure. 



2. Minor premise. By observation we detect only the visibly 

 less differentiated arising from the visibly more differentiated; 

 we see only a process of decreasing the visible differentiation. 



3. Conclusion. The visibly more differentiated must have 

 arisen from the visibly less differentiated, by decrease in the 

 visible differentiation of the latter. 



The conclusion is absurd; it cannot be drawn save for the 

 fact that while in the two premises we are talking of visible 

 differentiation and disintegration, in the conclusion the ground 

 is shifted to mean something entirely different — a sort of inner, 

 invisible, purely theoretical kind of differentiation -and simplicity 

 and disintegration. By putting in the word visible all the way 

 through, the absurdity is brought to light. All that we can 

 legitimately conclude from the two premises is that we have not 

 seen the process of evolution occurring. If we have seen nothing 

 but loss and disintegration, this is indeed the conclusion that we 

 must draw. But I believe that we cannot assert that this is all 

 that we have seen. 



