106 THE MEANING OF EVOLUTION 
less likely to be represented in the following genera- 
tion. The constant result of errors along this line 
would be to destroy the slow and preserve the swift, 
and in the course of time it is quite thinkable that 
only the swift should remain. As the movements 
grew more and more keen, even the slower of these 
would pass out, thus tending always to produce the 
succeeding generation from those who were most 
rapid, and hence most likely to transfer to their chil- 
dren a similar power. 
But there is another tendency of animals which 
leads them when frightened by their enemies to re- 
main quiet. If this impulse is obeyed thoroughly 
enough, it is easy to see how the owner of this habit 
might entirely escape detection by his enemy. Any 
restless animal unable to restrain his nervous agita- 
tion naturally betrays his presence and is picked off. 
The result of evolution along this line would be the 
exact reverse of the preceding. Those that lay most 
absolutely quiet would be the parents of succeeding 
generations, while those who were slow in coming 
to rest, or were indifferent about remaining quiet, 
were picked off, and their tendency eliminated from 
the future of the species. In this way many animals 
have come to keep entirely quiet in the presence of 
danger. It is not a sign of high intelligence. As a 
matter of fact, it is rather a stupid procedure, so far 
