236 PRINCIPLES OF POULTRY BREEDING 
ferent character. Variation is rather the result of changes taking 
place in existing characters, due to the changing relation between 
characters. 
The fact that individuals do vary makes improvement possible 
through selection and breeding which would otherwise be impos- 
sible. Indeed, without this factor there would be no chance for 
either improvement or deterioration; the type would be fixed in 
all its characteristics. 
Variations are of two kinds,—those which increase the useful- 
ness of the individual and those which are undesirable or create 
Fra. 120.—Barred Plymouth Rock chicks from the same mating and of the same age, 
showing morphological variation. 
an inferior condition. It is the duty and purpose of the breeder 
to select and intensify desirable variations whenever possible. 
Types of Variation.—The unit of variability is not the individ- 
ual, but the breed. The real measure of variation is the breed 
character. Four distinct types of variation have been described 
by Davenport.* The following brief discussion shows practical 
examples of these forms in poultry breeding and gives a clearer 
conception of variations. These types are (1) morphological, 
(2) substantive, (3) meristic, and (4) functional. 
Morphological variation has to do with differences in form or 
* Principles of Breeding,’ by Eugene Davenport. 
