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country in classical times with restricted environment, and contrast 

 it with the corresponding output of the whole enlarged modern world, 

 with its highly elaborated setting, there is occasion to wonder whether 

 the intrinsic capabilities of man have increased as much as his oppor- 

 tunities. It has always been easier for man to modify his surroundings 

 than to control his own heredity. To quote Joseph Jastrow, the 

 psychologist, "The fact that modern schoolboys are far better 

 equipped to withstand, utilize, and control the forces of nature than 

 was Aristotle, is not due to the superiority of the schoolboys, but to 

 the contributions of the Aristotles of past generations." 



Furthermore, the range of hereditary possibilities, particularly in 

 the case of man, may be considerably influenced by training or educa- 

 tion, which is a hopeful factor that perhaps cannot be entirely ac- 

 counted for either by heredity or environment. Education in itself 

 forms no part of the hereditary stream, since it is only the capacity 

 to acquire education in a yroper environment that can be handed on 

 from parent to child. In the 

 case of plants, and those ani- 

 mals whose automatic in- 

 stincts make it unnecessary 

 for them to learn how to live, 

 the factor of training or edu- 

 cation does not play as domi- 

 nant a part as in man. 



In the accompanying 

 diagram an attempt has been 

 made to indicate the mutual 

 dependence of heredity and 

 environment, in the forma- 

 tion of three different hypo- 

 thetical individuals. A, B, and C, represented by the rectangles in the 

 figure. When the parallel edge indicating the environment is shoved 

 back and forth, like a slide rule, different-sized rectangles result. 

 The act of shoving, particularly when the slide rule is shortened and 

 the "rectangular individual" is consequently enlarged, is much like 

 the process of education or training. In each case it will be noted 

 that neither the whole of the hereditary nor the whole of the envi- 

 ronmental edge is involved in the resulting individual. This cor- 

 responds with our common observation and conviction that neither 

 our capacities nor our opportunities are all ever entirely utilized. 



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A "slide-rule" diagram, showing how the 

 interplay between heredity and environment 

 may result in different individuals, A, B, 

 and C. 



