THE ABSENCE OF DOMINANCE 59 



Phenomena of this kind, which are usually spoken of as 

 " reversions," are a measure of the purity of a breed. 

 The more numerous they are the more impure the breed. 

 It is worth noting that, if a particular character in a breed 

 throws only one reversion, as the black Aberdeen-Angus 

 colour throws only the red reversion, then the breed 

 character and the reversion differ from each other in one 

 pair of characters only. 



But there are characters which are not to be bred pure 

 even by the most persistent and long-continued efforts. 

 The example first made clear is the colour of the Blue 

 Andalusian breed of fowl, which is thus described by 

 Professor Bateson : " Andalusians are in general colour 

 what fanciers call blue — namely, a diluted black. In the 

 cocks the hackles and saddle feathers are full black, and 

 the feathers of the breast are edged or " laced " with 

 black. The hens are blue, laced with black more or less, 

 all over. This breed is recognized by the fanciers as never 

 breeding true to colour. When blue is bred with blue 

 three colours are produced, blacks, blues, and a peculiar 

 white splashed with grey." 



In 1902 Professors Bateson and Punnett learned from 

 a breeder of these fowl that her blue birds of that year 

 had thrown 36 blues, 22 blacks, and 17 whites ; and, 

 having procured birds of all three kinds, they found that 

 their blue birds also threw blues, blacks, and whites in 

 similar proportions, namely, 42, 19, and 22, while the 

 other two kinds, black and white, bred true. They also 

 found that the blacks and the whites threw blue Andalu- 

 sians when mated with each other. 



Stated in the usual order, this means that blacks mated 

 with whites throw hybrids different from both : from which 

 it is to be inferred that there are at least two pairs of 



