44 MENDELISM AND 



When two or three or more differences are studied 

 we find that they are usually inherited separately 

 without connexion with each other, although in 

 some cases they are connected or coupled. The 

 facts of Mendelism are of great interest and im- 

 portance, but we have to consider the general theory 

 based on them. This theory is that characters 

 are generally separate units which can exist side by 

 side, but do not mingle, and cannot be divided into 

 parts. When an apparently single character shows 

 itself double or treble, it is concluded that it has 

 not been really divided, but consists of two or three 

 units (Castle). Further, although Mendelism in 

 itself shows no evidence of the origin of the characters, 

 it assumes that they arose as complete units, and 

 one suggestion is that a dominant factor might 

 at some of the divisions in gametegenesis pass 

 entirely into one daughter cell, and therefore be 

 absent from the other, and thus individuals might 

 be developed in which a dominant character was 

 absent. Bateson in his well-known books, Mendel's 

 Principles of Heredity, 1909, and Problems of Genetics, 

 1913, discusses this question of the origin of the 

 factors which are inherited independently. The 

 difficulty that troubles him is the origin of a dominant 

 character. Naturally, if he persists in regarding 

 the determinant factor as a unit which does not 

 grow nor itself evolve in any way, it is difficult 

 to conceive where it came from. The dominant, 

 according to Bateson, must be due to the presence 

 of something which is absent in the recessive. He 

 gives as an' instance the black pigment in the Silky 

 fowl, which is present in the skin and connective 

 tissues. In his own experiments he found this was 



