536 
BIOLOGY AND HUMAN PROGRESS 
lines following a general pattern with an infinite number of 
variations possible. It is these very small variations that 
each one has that enable the expert to identify two finger 
prints made by the same person. The United States Gov¬ 
ernment has selected finger prints as the surest way to identify 
its soldiers and many banks have long used the finger-print 
method of identification. 
Is it possible to predict what human beings will inherit 
from their parents? In a very general way we can answer 
this question in the affirmative. One of the most striking 
ways in which this is seen is in a study of the inheritance of 
certain defects, such as feeblemindedness. This is a disease, 
the cause or causes of which are not well understood, but we 
do know that such people are usually unable to earn a living 
and have to be supported by public taxation. A large pro¬ 
portion of their children inherit this same mental defect. 
The scientific study of heredity has proved that this is the 
case and always will be so. It remains for us to decide 
what is the best thing to do with such people. What is true 
of imbecility is not true of most other diseases. 
General ability and a tendency to industry and thrift are 
inherited by a large proportion of the children of the parents 
that possess these admirable traits. The men and women 
who possess such mental traits carry on the business of the 
country and pay taxes not only to support the government 
but also to care for the idle, the shiftless, and the criminal. 
If we have inherited these together with other valuable traits 
of character, we should take care that they are passed on to 
our children in order that the next generation shall possess 
enough men and women who will be able to advance human 
progress beyond our best efforts. 
408. Environment. — All through this book attention has 
been directed to the environment in which the animal or plant 
lived that was being studied. The same fact was empha¬ 
sized in the beginning of this section dealing with human 
