226 PRINCIPLES OF POULTRY BREEDING 
portionately greater variation in the transmitted qualities; hence 
the necessity of breeding from parents as purely bred as it is pos- 
sible to obtain them. By eliminating alien blood the desired prop- 
erties become dominant, so to speak; that is, they become intensi- 
fied, and there are fewer contending characteristics to crowd them 
out. The longer a family of individuals can be bred purely, so 
much more powerful will its dominant traits become. (The mating 
and selection of individuals is discussed in the next chapter.) 
The influence of environment on future generations is im- 
portant. All conditions and operations included in the care 
and management of birds will more or less influence the indi- 
vidual, and also leave their mark upon the offspring; lack of 
proper environment may tear down and soon destroy all that has 
been accomplished by years of hard work in selection and breed- 
ing; hence the necessity of understanding the natural requirements 
of the birds before experimenting with the laws of breeding. 
Controlling Factors.—The influences which are active in the 
propagation or breeding of poultry are numerous and varied. 
A. A. Brigham* has grouped these under three heads, as follows: 
All characteristics which are transmitted from parent to off- 
spring, this group being termed inheritance. 
All characteristics which are due to external conditions sur- 
rounding the individual, these being termed environment. 
All characteristics which are functional in nature, and in many 
cases influenced by man’s activities. In demonstration these func- 
tions are nearly all influenced directly by man, while in the wild 
state they are given freedom of exercise. This group may be 
termed functional activities. ; 
Inheritance.—Inheritance, in the sense here used, is a much 
broader term than when employed to define the law of heredity. 
It embraces all the powers, qualities, and characteristics which are 
transmitted from the parents to the progeny through the egg, the 
combining or merging of traits possessed by both male and female 
into one, and the new characteristics of the resulting chicks. 
This factor of inheritance affects or influences a great variety 
of conditions. Among these are the shape and size of the body, 
and the quality and color pattern of the plumage; all internal 
bodily functions, such as the development of the digestive system, 
the power of the circulatory system, and the capacity of the 
respiratory system; the texture and structure of muscles, bones, and 
* “Progressive Poultry Culture,” by A. A. Brigham. 
