Darwin s Artificial and Natural Selection 163 



breeder has obtained his results in artificial selection. For 

 instance, the long-tailed variety of the domestic cock of Japan 

 owes its existence, it is claimed, to skilful selection, and not 

 at all to the circumstance that, at some period of the race's 

 history, a cock with tail-feathers six feet in length suddenly 

 and spasmodically appeared. 



Weismann continues: "Now what does this mean? Simply 

 that the hereditary diathesis, the germinal constitution (the 

 Anlage) of the breed was changed in the respect in question, 

 and our conclusion from this and numerous similar facts of 

 artificial selection runs as follows : by the selection alone of the 

 plus or minus variations of a character is the constant modifi- 

 cation of that character in the plus or minus direction deter- 

 mined. Obviously the hereditary diminution of a part is also 

 effected by the simple selection of the individuals in each 

 generation possessing the smallest parts, as is proved, for 

 example, by the tiny bills and feet of numerous breeds of 

 doves. We may assert, therefore, in general terms : a defi- 

 nitely directed progressive variation of a given part is pro- 

 duced by continued selection in that definite direction. This 

 is no hypothesis, but a direct inference from the facts and 

 may also be expressed as follows : by a selection of the kind 

 referred to the germ is progressively modified in a manner 

 corresponding with the production of a definitely directed 

 progressive variation of the part." 



So far there is nothing essentially new offered, since Darwin 

 often tacitly recognized that the standard of variation could 

 be raised in this way, and in some places he has made 

 definite statements that this will take place. Weismann 

 thinks that after each selection, fluctuation will then occur 

 around a higher average (mode). He says "that this is a 

 fact," and is proved by the case of the Japanese cock. It 

 need scarcely be pointed out that it is an assumption, based 

 on what is supposed to have taken place in this bird, and is 

 not a "fact." 



