CHAPTER IX 



THE EVOLUTIONARY CAREER 



I. EVOLUTION IN GENERAL 



{a) Let some physical system undergo repeated changes in 

 such a way that these changes have, on the average, some particular 

 direction, or tendency : we shall say, then, that the system 

 " evolves." 



(b) And since the changes may occur along different directions, 

 or exhibit different tendencies, it is plain that systems may 

 *' evolve " differently. 



(c) Let a physical system undergo repeated changes that have, 

 on the average, no tendency, or direction : then the system does 

 not '' evolve." (Presently we shall consider more fully what is 

 to be meant by the word '* evolve.") 



Familiar and trivial examples of these statements are afforded 

 by study of the card games called " Patience " ones. The pack 

 of cards is shuffled (or mixed up, so that inspection shows no 

 particular order) and then it is distributed according to certain 

 rules, or conventions. As the distribution (or the repeated 

 changes of the card-system) proceeds the cards come to exhibit 

 a particular arrangement — which may be said to " evolve." And 

 there are many different kinds of " Patience " games so that the 

 same system (or pack of cards) may be made to '' evolve " in as 

 many different ways, as there are sets of rules, or conventions. 



Let a pack of cards arranged as they " come out " in a successful 

 " Patience " game be repeatedly shuffled. As the shuffling 

 proceeds the particular arrangement disappears. Then, as shuffl- 

 ing still proceeds there will be a very great number of arrange- 

 ments, but any one of these will occur as often as any other 

 one and there will be no tendency in these arrangements. 

 While the particular arrangement brought about in the successful 

 game is disappearing we may say that there is an '' evolution " 

 — in a different sense (from " order " to disorder) — from that of 



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