An Introduction to a Biology 



Let us consider these objections one by one. With re- 

 gard to the first I would say, what I have said before, that 

 the service which Mendelian theory has done to progress 

 in the study of heredity lies partly in the facts which it has 

 accounted for, and partly in the method which it has intro- 

 duced ; and that even if Mendel's Law has a limited applica- 

 tion, his method has a great future. 



The second objection is merely a detailed expression of 

 the first ; it states in what the limitation lies. Mendel's 

 Law is said to apply to a very few characters, of which colour 

 stands out pre-eminently among the rest. And although it 

 is true that the list of characters whose inheritance can 

 be described in terms of Mendel's Law comprises many other 

 characters than colour, e.g. the shape of the comb in fowls, 

 the waltzing habit in mice, and even, lately, resistance to 

 disease in plants, it is nevertheless true that the number of 

 characters to which Mendel's Law can be said to apply is 

 very small indeed when compared with the number of char- 

 acters which go to make up an organism. And it can be 

 said with some truth that the characters with which the 

 hybridiser can deal are in a sense superficial. When we 

 cross an albino and a waltzing mouse the result is to our 

 eyes remarkably different from either parent ; it is like a 

 wild mouse, but it is a mouse. The feature in which it 

 differs from its parents are its colour, its progression it 

 never waltzes like one of its parents and to a certain extent 

 its vigour and temperament, for it is healthier and wilder 

 than either parent : but it is still a mouse. The charge is 

 brought against the hybridiser that he can only stir up the 

 surface, but that he cannot disturb the depths. My answer 

 to this objection is that it is entirely well founded ; that 

 there certainly are two sets of characters, one which can 

 be affected by hybridisation, and another, a much larger 

 one, which cannot, and that it is legitimate to regard the 

 former as upper and the latter as lower. By saying this I 

 do not mean to subscribe to the view that recently arisen 



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