THE HEREDITY OF SEX 45 



recessive to the white-skin character of the Brown 

 Leghorn, and he assumes that the genetic properties 

 of Oallus bankiva with regard to skin pigment are 

 similar to those of the Brown Leghorn. Therefore 

 in order that this character could have arisen in 

 the Silky, the pigment-producing factor P must be 

 added and the inhibiting factor D must drop out 

 or be lost. He says we have no conception of the 

 process by which these events took place. 1 Now 

 my experiment in crossing Silky with bankiva 

 shows that no inhibiting factor is present in the 

 latter, so that only one change, not two, was necessary 

 to produce the Silky. Mendelians find it so difficult 

 to conceive of the origin of a new dominant that 

 they even suggest that no such thing ever occurs : 

 what appears as a new character was present from 

 the beginning, but its development was prevented 

 by an inhibiting factor : when this goes into one 

 cell of a division and leaves the other free, the sup- 

 pressed character appears. This is the principle 

 proposed to get over the difficulty of the origin of a 

 new dominant. All characters are due to factors, 

 and all factors were present in the original ancestor 

 say Amoeba. Evolution has been merely ' the 

 rejection of various factors from an original complex, 

 and a reshuffling of those that were left.' Professor 

 Lotsy goes so far as to say that difference in species 

 arose solely from crossing, that all domestic animals 

 are of mixed stocks, and that it is easier to believe 

 that a given race was derived from some ancestor 

 of which all trace has been lost than that all races 

 of fowls, for example, arose by variation from a single 

 species. But the evidence that our varieties of 



1 Problems of Genetics, p. 85. 



