DIVERSE INHERITANCE. 41 



transmissible type. The reproductive system is 

 " extremely sensitive " to very slight changes, 

 and is often powerfully affected by circumstances 

 which otherwise have little effect on the indivi- 

 dual (Origin of Species , p. 7). Various animals and 

 plants become sterile when domesticated or sup- 

 plied with too much nourishment. The native Tas- 

 manians have already become extinct from sterility 

 caused by greatly changed diet and habits. If, 

 as Mr. Spencer teaches, continued culture and 

 brain-work will in time produce lessened fertility 

 or comparative sterility, we may yet have to be 

 careful that intellectual development does not 

 become a species of suicide, and that the 

 culture of the race does not mean its extinc- 

 tion or at least the extinction of those most 

 susceptible of culture. 



The reproductive elements are also disturbed 

 and modified in innumerable minor ways. 

 Changed conditions or habits tend to produce 



