484 THE CHANGING WORLD 



Although it may be necessary to extend the duration of observa- 

 tion in order to detect the occurrence of something different as 

 happening, nevertheless, it always comes about in the end. The 

 apparently stationary hour-hand of a clock, for example, is known to 

 shift its position during the day, in spite of its appearance of stand- 

 ing still. 



That no structure or action remains constant and enduring is 

 particularly evident in living things, in which change is inevitable 

 from the cradle to the grave, not only in mankmd but also in the 

 daily life of every animal and plant. 



Furthermore, if it were possible to take a complete census of all 

 the different kinds of organisms represented on the earth today, for 

 comparison with similar censuses taken during the different geologi- 

 cal periods, sweeping changes in the character of whole groups would 

 at once be apparent. Even with the partial census which biologists 

 have been able to make of organisms laiown to have existed in the 

 past, as contrasted with the catalogue of living forms thus far dis- 

 covered, it is proven without a doubt that the Law of Change is now, 

 and always has been, everywhere in constant operation. 



The causes, or sequences of events, leading up to all sorts of changes 

 are naturally diverse and numerous. With organisms they may be 

 inborn, that is, genetic in character, or largely external and environ- 

 mental, but in any case, the fact of change with its consequences 

 is observable and can be analyzed, even though the underlying 

 causes that bring these changes about are often uncertain and un- 

 known. 



Sometimes changes, in themselves slight, may have far-reaching 

 consequences. For example, when single-celled organisms, accus- 

 tomed from time immemorial to divide periodically each one into 

 two individuals, discovered the great advantages of partnership and 

 remained attached to each other after fission occurred, instead of- 

 separating and going their independent ways, right then was born 

 the pregnant idea of tissues and organs. The device of cell multipli- 

 cation opened up consequent possibilities of the working together of 

 parts for greater effectiveness, through the fertile principle of "divi- 

 sion of labor." This change was a great historical event in the world 

 of life, with extensive sequels. 



Again, when by gradual changes the shift from a single parent to 

 the sexual method of two parents came about, another great bio- 

 logical epoch began in which,' by utilizing two hereditary streams 



