CHAPTER XXV 



CHANGE FACTORS. INTRODUCTION 



Change has already been contrasted with diversity by citing the 

 analogy of the kaleidoscope (p. 187). Another analogy may help to 

 emphasize this difference. If one were to shuffle and deal a very elabo- 

 rate deck of cards, the hands dealt would show very great diversity, but 

 there would be a certain statistical limitation to the number of possible 

 combinations of cards. After a time the whole series of possible com- 

 binations would be dealt out and the series would go on repeating it- 

 self, and nothing new would appear so long as the cards remained un- 

 changed. Add a new card or a new series of cards, or merely change 

 some of the spots on a card, and at once the whole character of the 

 combinations produced would be altered. Dealing an unchanged deck 

 of cards is the sort of thing that the diversity mechanism (sex) does, 

 but the mutation mechanism actually adds new cards or alters the 

 spots. Changes in the germinal substances themselves are called 

 mutations. Hence mutation is the change mechanism. 



CHANGING VIEWS AS TO THE ORIGIN OF 

 NEW HEREDITARY CHARACTERS 



Lamarck believed that all evolutionary change was initiated in the 

 body (soma) directly or indirectly in response to environmental stimuli, 

 causing increased or decreased functioning of parts. He had no theory 

 as to how such changes could be inherited, but assumed that they were. 

 This belief is embodied in his theory of the inheritance of acquired 

 characters, known as the "Lamarckian theory." 



Charles Darwin also believed that all variations that are frequent 

 enough to serve as the raw material for selection originated in the soma 

 in response to differences in the environment or indirectly, to changes 

 in the amount of use to which a given part was put. To account for 

 such changes being hereditary, he proposed a theory with which he was 

 not very well satisfied, for he called it "the provisional theory of pan- 

 genesis." According to this view, each part of the organism is con- 

 tinually giving off into the blood stream minute particles, "pangenes," 

 each of which is characteristic of the particular status of a part of the 

 organism at the time when the pangene was given off. Thus a 

 strengthened muscle or a more efficient eye, each resulting from in- 



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