An Introduction to a Biology 



based on a firm belief in the Law of Diminishing Individual 

 Contribution ? 



These three cases show how widespread is belief in this 

 Law ; and they also show that in these three cases at least 

 it is not valid. 



The difference between the expectation based on this 

 Law 1 and the accurate knowledge of what actually takes 

 place (which it is the business of Mendelian investigation 

 to supply) is the same as the difference between common 

 sense and science, and the same as the difference between 

 that which stands to reason and that which rests on 

 evidence. 



(6) MENDEL'S LAW 



I do not propose to discuss here the statement that the 

 time has not yet come when we are justified in speaking 

 of Mendel's Law, nor to inquire into the meaning of this 

 statement : the question I propose to answer is, " What 

 is the essential feature of that which is called Mendelism 

 by those who believe in it, and Mendelianism by those who 

 do not ? " 



I divide definitions of the Law into two primary cate- 

 gories : 



(i.) Suitable for those who desire to establish the 



invalidity of the Law. 

 (ii.) Suitable for those who wish to discover whether 



Mendelism has helped us or is likely to help us 



to attain to a more intimate knowledge of 



heredity. 



There is no difficulty in finding a definition of the first 

 class : a very satisfactory one is one which binds the Men- 

 delian down to the Law exactly as enunciated, and the 

 description of the phenomena exactly as given by Mendel 



1 Huxley must have been thinking of some such Law as this when he 

 made the remarkable statement that science was organised common sense. 



176 



