370 FOOT-NOTES TO EVOLUTION, 
the intense practicality of the senses and the intellect. 
They tell us the truth as to external things, in so far as 
this truth has been essential to our ancestors. Those of 
our predecessors who did not “ see things 
as they really are,” to the degree that 
their life processes demanded, have died, 
leaving no descendants. Our own ancestors, through 
all the generations, have been creatures of adequate sen- 
sations and of adequate power of thought. Were it not 
so, they would have been unable to cope with their en- 
vironment. In other words, the sensations their brains 
translated into action were truthful enough to make ac- 
tion safe. That our ordinary sensations and our induc- 
tions from them are truthful so far as they go, is proved 
by the fact that we have safely trusted them. This is 
shown also by the instruments of precision which are 
the tools of science. That instruments of precision like- 
wise tell the truth, is shown by the fact that we can 
trust our lives to them. That they are more trust- 
worthy than the unaided senses, is shown by their greater 
safety. 
But while our senses tell the truth as to familiar 
things, as rocks and trees, foods and shelter, friends and 
enemies, they do not tell the whole truth. They go 
only as far as the demands of the environment have 
compelled them to go. Chemical composition they do 
not show. Objects too small to be handled are too 
small to be seen. Bodies too distant to be reached are 
never correctly apprehended. Accuracy of sense grows 
less as the square of the distance increases; and sun 
and stars, clouds and sky, are in fact very different from 
what they seem. 
In matters not vital to action exact knowledge loses 
its importance. It is perfectly safe, in the ordinary 
affairs of life, to believe in witches and incantations, 
Practicality of 
the senses. 
