THE BEAVERS OF NORTH AMERICA 831 
stand and account for what they do if we would 
only start out with the idea that both animals and 
birds, though governed by certain very definite laws, 
have the use of a limited free intelligence, which 
enables them to take advantage of conditions and 
accomplish things which are apparently not in 
keeping with what might be done by others of the 
same species. It is this individuality which helps 
animals to adjust themselves to new conditions, 
whereas if they adhered too strictly to the rules 
which have governed them in the past they would, 
through the lack of power of free thought, fall easy 
victims to new and adverse conditions. 
Having now seen what the beaver’s lodge is like, 
we may take into consideration the dam which is 
the direct adjunct to the house or rather to the 
more advanced type of house. Just when or how 
dams first began it is impossible for us to say, but 
the chances are they are the result of a very gradual 
development through perhaps thousands of years. 
So far as I can learn the beaver of the old world 
did little or no important dam building, but his 
close cousin on the American continent has without 
doubt been building them for a very long time 
and with some very extraordinary results. (These 
will be dealt with in another chapter.) 
As already stated the primary objects of the 
dams appear to be four-fold, the most important 
being apparently that water may be maintained 
at a constant level in order that the house shall 
