418 V. THE NATURE OF EVOLUTION 



the change in the brain pattern even if the effect of use or disuse is 

 not involved, Therefore, the addition of the effect of use and disuse 

 to that of the hormones may result in a striking change in the mental 

 pattern, and when the effects continue to have their influences in 

 successive generations, the mental characteristics will become strong 

 and fixed and accordingly inheritable. 



As to the inheritance of memory, a detailed consideration was 

 made in the beginning of this Part. The memory in our brain is 

 considered to be a structural change in the protoplasm protein of 

 brain cells. Such a structural change can be transmitted to the newly 

 formed proteins ; thus the memory can be transferred successively to 

 newly formed proteins or protoplasm. If this change is transmitted 

 to germ cells by protoplasm particles, namely by virus-like agents, 

 and if the changed structure does not return to the original during 

 the development of the germ cell to the young individual, the memory 

 can be inherited by the young. The memory of phylogeny has been 

 inherited from generation to generation for a dreadful long span of 

 time as the ontogeny. Moreover, every instinct of creatures must 

 depend upon the memory thus inherited for generations. 



One may say that not only do English children have to learn their 

 own language, but they learn it no quicker than they would learn 

 French if brought up from the first in a French-speaking household, 

 and that this fact demonstrates evidently the failure of the inherit- 

 ance of memory. However, if this is true, it can be considered that 

 minute structural differences corresponding to the memory of difference 

 between French and English cannot be transmitted, but that the faculty 

 to learn words as a whole must be inherited and strengthened when 

 man continues to speak a language. 



A number of experimental evidences suggesting the possibility 

 of the inheritance of habit has been presented by several workers, but 

 mostly have been regarded as very doubtful like other experimental 

 data concerning the inheritance of acquired character. Since the struc- 

 tural change in the protoplasm in central nervous system must also 

 be reversible, it should naturally follow that the clear demonstration 

 of the inheritance of habitude likewise failed when observations were 

 made only for a few generations. From the theory of the writer thus 

 far described the inheritance of habitude seems to be a natural con- 

 sequence. The splendid advancement of animals, especially of mankind 

 as seen in the present day, might not have occurred without the 

 inheritance of habitude. 



Domestic animals such as dogs and horses are very faithful as 

 well as obedient to their masters. This may probably not only due 

 to the artificial selection, but also to the inheritance of habitude. 

 Thus, habit does become a nature. 



