Heredity and the Law of Evolution. 287 



are preserved and transmitted without modification. Nothing in- 

 creases, nothing diminishes, nothing changes. 



On the other hand, suppose both evolution and heredity, and 

 then life and variation become possible. Evolution produces 

 physiological and psychological modifications ; habit fixes these in 

 the individual, heredity fixes them in the race. These modifica- 

 tions as they accumulate, and in course of time, become organic, 

 make new modifications possible in the succession of generations ; 

 thus heredity becomes in a manner a creative power. This fact 

 of the heredity of acquired modifications has made its appearance 

 often in the course of the present work ; though we shall have to 

 examine it in detail further on, it will be useful to dwell upon it 

 here for a little while, as it will give us a better understanding of 

 the relations between heredity and the law of evolution. 



In the physiological introduction we showed that acquired 

 modifications can certainly be transmitted. We have seen, for 

 instance, that animals artificially made epileptic transmit that 

 morbid disposition to their descendants. We have also seen 

 that this point is possessed of some difficulty, for facts seem to 

 show that these deviations from the type tend to return to the 

 normal state, and that the law is, that accidental states are not 

 perpetuated, but that, after subsisting for a few generations at 

 longest, they first grow fainter, and then disappear. Thus we 

 should return to the difficulty we met at the outset, that we should 

 have evolution without heredity, or at best with only a restricted 

 heredity, yielding no results of any importance. The difficulty, 

 however, is only an apparent one. Even were we to accept the 

 hypothesis of a return to the primitive type, which is the one most 

 at variance with our theory, it will be observed that this return 

 has no place except when a race is lefj: to itself. The experience 

 of breeders shows that certain physiological characters can be 

 thoroughly fixed and perpetuated by continual selection, notwith- 

 standing some exceptions and cases of reversion ; but educations 

 acts upon the mental faculties precisely as the breeder's art acts 

 on the organism and its functions. We shall see that the capacity 

 for seizing abstract ideas, and for complying with the conditions 

 of civilized life, becomes fixed only after a considerable length of 

 time in certain races ; these, left to themselves, return also to the 



