An Introduction to a Biology 



lation cannot be permanent unless the Mendelian is pledged 

 not to change his theory in the smallest degree. I hold 

 that, in the first place, Mendelism has, as I have shown, a 

 wider signification namely, that it embraces the method 

 as well ; and secondly, that no Mendelian can be expected 

 to take the pledge demanded, if by doing so he believed, 

 as he probably would, that he would be prevented from 

 attaining his end. It is idle to accuse him of inconsistency. 

 What should we think of the consistency of a well-digger 

 who died of thirst because he would stick to his spade although 

 only a few feet of granite separated him from watei; ? 



And what right have we to expect that the demon should 

 pledge himself not to alter his theory of the nature of atoms, 

 if he hopes that by being free to alter it he will attain a 

 knowledge of them that will enable him to live in a warm 

 compartment without having to do any work for it ? What 

 right has a physicist to expect a demon not to alter his 

 theory, on the ground that such an alteration makes it 

 exceedingly difficult for him (the physicist) to use the theory 

 as a basis for statistical calculation ? 



(c) THE DIFFERENCE BETWEEN MENDEL'S LAW AND THE 

 LAW OF CONTRIBUTION 



Now that we come to discuss the difference between 

 Mendel's Law and the Law of Diminishing Individual Con- 

 tribution, we must clearly understand that by Mendel's 

 Law we mean the theory associated with that name, and 

 not the method. 



These two Laws resemble each other in being physiological, 

 in that they attempt to picture the way in which characters 

 are represented in the germ-cell. But they differ profoundly 

 in the picture which they draw. The difference is so obvious 

 that it is hardly necessary to speak about it. A remark 

 on the difference between the predictions of the two Laws 

 as to the nature of the offspring of extracted recessives will 

 suffice. Suppose that two hybrid mice with grey coats 



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