Ill 



SOURCES OF CHANGE 



All of the material things in the world, as far 

 as we know, are due to the action of certain forces 

 upon certain materials. Even the rocks may be 

 classified according to the substances of which 

 they are formed and the means whereby they were 

 shaped. They may be granitic or basaltic, lime- 

 stones, sandstones, or shales; they may be igneous 

 or sedimentary or metamorphic. Obviously a mod- 

 ification of the materials composing them or of 

 the forces shaping them must have given rise to 

 different products. So too in the case of man-made 

 things. If we desire a given result we must adhere 

 strictly to the materials and processes which give 

 that result. If we are careless of our specifications 

 we cannot expect a uniform product. 



The organism is subject to these same condi- 

 tions. It is a product of a certain complex type of 

 matter responding to various conditions of environ- 

 ment. The living matter of which organisms are 

 composed may be of many different kinds and the 

 conditions to which it responds are no less varied, 

 hence the great variety of living things which 

 populate the earth. May we conclude also that a 



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