TYPES OF VARIATION 237 
size which are quantitative in character. This type of variation 
is very common, a simple example being two chicks which are 
exactly alike except that one is larger than the other (Fig. 120). 
In this instance there is no difference in the characteristics of the 
two individuals, but merely the fact that in one growth had been 
more rapid and proceeded farther than in the other. This type 
of variation is especially important in breeding for large-sized 
birds for market poultry. 
Substantive variation is shown by differences in the quality of 
different individuals as distinct from mere size and form. Such 
Fic. 121.—Two birds of the same parentage, showing variation in color only—an 
example of substantive variation. 
variations are qualitative rather than quantitative in nature. This 
type of variation refers to the constitution or nature of the indi- 
vidual, and is manifested by differences between individuals of 
the same breed (Fig. 121) and between different breeds. In regard 
to the character of flesh, some are hard (Games) and others soft 
(Brahmas). In the quality and taste of the meat, wild and domes- 
tic species differ widely. 
Birds of the same breed differ in their power to withstand cold. 
Individuals differ as to their power to resist certain communicable 
diseases. 
