400 
MAN AND THE OTHER ANIMALS 
Some of the men who have made a special study of the 
fossil remains of man in the rocks believe that man began 
living in Europe about 25,000 years ago. This is their esti¬ 
mate of the length of time that has passed since the rocks 
were formed in which are found jaw bones or the bones of 
the legs and arms. In all such cases so far there has been 
no difficulty in recognizing these fossil bones as belonging 
to man, although the races of people who lived fifteen or 
twenty thousand years ago no longer exist. 
The earliest homes of man must have been the shelter of 
trees and an occasional cave, and it is in certain caves in 
Spain and France that many early records of man are to be 
found. There is no record of when man first began to use 
fire or to build definite shelters. In fact, both these neces¬ 
sities in our cold climate were not as important to early 
man, because he appears to have wandered about in tropical 
and sub-tropical regions. This was even true of the climate 
of Spain and France in the period when he lived in the caves 
which have become famous for their many records of the 
early life of man. With the coming of the glacial period, the 
climate of all northern Europe and northern America 
became much colder and the men who lived in regions that 
were influenced by the southward movement of the ice 
sheets had to adopt some means of keeping warm or perish. 
But as soon as the number of men became so great that 
they needed to go farther for the necessary food, we may 
suppose that protective measures were gradually used. 
Moreover, the same forces that compelled early man to 
migrate have continued to impel man to move out into un¬ 
known parts to see if he can find an easier place to live. We 
shall see how this has come to have a vital influence upon 
our own lives as we examine more fully into man’s life 
processes. 
We have lived in houses heated in winter so long that we 
had begun to feel that it would be impossible to get along 
