92 SEX AND HEREDITY 



of a man's eye is but little affected by his environment, 

 but is almost entirely determined by his innate constitu- 

 tion. On the other hand, the skill of a pianist is plainly 

 dependent both on his innate mental and physical qualities, 

 and on the fact that he has been provided with the 

 opportunity of learning to play the piano. 



FIG. 47. 



Diagrams of the stream of life A under its simplest condition, as found in 

 some of the lower animals and plants, where there is only one parent ; B under 

 ordinary conditions, where two parents are concerned with each act of repro- 

 duction. 



The base lines represent the continuous streams of germ-plasm, the uprights 

 the bodies produced by them. In A the streams of germ-plasm flow independently, 

 giving off bodies at intervals. In B bodies are produced only at the intersection 

 of two streams. 



Now if our views as to the relation between individuals 

 and the germ-plasm which gave rise to them are correct, 

 only the innate qualities can be inherited, for the germ- 

 plasm produces the body, not the body the germ-plasm. 

 For example, take two children of equal (innate) musical 

 capacity, and put one in a desert island where he will never 

 see a musical instrument, and train up the other to music 

 as a profession ; there is no reason to believe that the 

 children of the professional musician will show greater 



