34 THE FACTORS OP ORGANIC EVOLUTION. 



powers which do not subserve self-preservation in appreci 

 able degrees, does development by natural selection appear 

 impracticable. 



It is a fact recognized by Mr. Darwin, that where, by 

 selection through successive generations, a part has been 

 increased or decreased, its reaction upon other parts 

 entails changes in them. This reaction is effected through 

 the changes of function involved. If the changes of 

 structure produced by such changes of function, are 

 inheritable, then the re-adjustment of parts throughout the 

 organism, taking place generation after generation, main 

 tains an approximate balance ; but if not, then generation 

 after generation the organism must get more and more out 

 of gear, and tend to become unworkable. 



Further, as it is proved that change in the balance of 

 functions registers its effects on the reproductive elements, 

 we have to choose between the alternatives that the regis 

 tered effects are irrelevant to the particular modifications 

 which the organism has undergone, or that they are such 

 as tend to produce repetitions of these modifications. The 

 last of these alternatives makes the facts comprehensible ; 

 but the first of them not only leaves us with several 

 unsolved problems, but is incongruous with the general 

 truth that by reproduction, ancestral traits, down to minute 

 details, are transmitted. 



Though, in the absence of pecuniary interests and the 

 interests in hobbies, no such special experiments as those 

 which have established the inheritance of fortuitous varia 

 tions have been made to ascertain whether functionally- 

 produced modifications are inherited ; yet certain apparent 

 instances of such inheritance have forced themselves on 

 observation without being sought for. In addition to 

 ether indications of a less conspicuous kind, is the one I 

 have given above the fact that the apparatus for tearing 

 and mastication has decreased with decrease of its function, 

 alike in civilized man and in some varieties of dogs which 



