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: dy the selection alone of the 
plus or minus variations of a character 1s 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: dy a selection of the kind 
referred to the germ is progressively modified in a manner 
corresponding with the production of a definitely directed 
progressive vartation 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.” 
