534 BIOLOGY AND HUMAN PROGRESS 
After you have made these comparisons, you realize that 
you are unlike both parents in that you have some features 
which are lacking in either your father or your mother. 
The total of the like parts and traits which are the same as 
in your father make up what you have inherited from your 
father; and the total of the parts and traits which are the 
same as those in your mother, make up what you have 
inherited from your mother. Thus we inherit from both 
parents. 
But there are usually found some structures and char¬ 
acteristics that do not represent anything found in either 
parent. If such are carefully analyzed, it is usually dis¬ 
covered that they exist in some of the grandparents. It is 
always interesting to try to locate their origin. 
This study of our hands and other parts of our body leads 
to an important general statement. All the parts of our body 
with their individual peculiarities have existed in other human 
beings and these persons were your immediate ancestors (parents, 
grandparents, great-grandparents, etc.). 
This explanation of heredity applies to all animals and 
plants, so that we can study heredity in our war gardens or 
with our pet animals. 
There is a limit to the differences that exist between child 
and parent, and these differences under normal conditions 
produce changes that would never make the structure a new 
one; for example, the finger is always a finger, and hair is 
always hair. Heredity is thus a descriptive, technical word 
used to explain the like parts between child and parent. 
During the past fifteen years, there has been a great deal 
of experimental work upon plants and animals in an attempt 
to explain just how an offspring inherits from its parents. 
It is impossible to record these experiments here because 
they would make a book several times as large as this one. 
It is too soon to be entirely certain just what these studies 
mean. When we do understand, then we can explain heredity. 
