HEREDITY 
535 
Sufficient progress has been made in the explanation of 
heredity so that those who raise prize horses, cattle, sheep, 
apples, berries, wheat, and other products can be reasonably 
certain that their efforts will be successful. The average 
American cow gives 3100 pounds (a pound is about one 
pint) of milk a year; while one cow has a record of giving 
30,000 pounds in a single year. If the farmer can sell 
his milk for five cents a quart, the milk of the average cow 
would be worth $77.50 a year; while the prize cow would 
bring its owner $750. The variation in the amount of milk 
that a cow gives is an inherited character; so if the breeder 
selects animals that are big milkers, he can secure cows that 
will produce more milk than the breeder who does not make 
such a selection. 
In a similar manner all well-informed men who deal with 
animals and plants seek to secure certain results, but they can¬ 
not produce a new kind of animal or plant. They simply 
magnify some of the parts and reduce others by a detailed 
study of the way these parts are inherited. Sometimes they 
spend years and are not successful and often the desired 
result does not remain fixed or permanent but disappears 
in the next generation. This is a phase of biology that you 
should try to keep in touch with for both its interest and 
value. 
407. Relation of Variation and Heredity to Human Prog¬ 
ress. — In a general way this has already been indicated, 
especially where the practical value in raising larger crops of 
hay or wheat or in producing more milk was mentioned. But 
we are also interested to learn how variation and heredity 
apply to man. Your study of your hands and the other parts 
of your body demonstrated to you that you had inherited 
certain peculiarities from your parents. As you studied 
these similarities, you found that there were small differences 
or variations. This is well illustrated in the study that is 
being made of finger prints. Each one of us has these minute 
