28 Lvolution and Adaptation 
parts of the body mainly in that they are made of different 
compounds having different properties, as the above com- 
parisons have shown. But the regulations of the machine 
have been added to it by man on account of their useful- 
ness to himself, and are not properties of the material of 
which the machine itself is composed. This shows, I think, 
the inappropriateness of making any comparison between 
these two entirely different things. 
If, then, we find the comparison between machines and 
organisms unprofitable, can we find any other things in 
inorganic nature that can be better compared with the 
phenomenon of adaptation of the organism? The following 
phenomena have been made the subject of comparison from 
time to time. The bendings, which are gradually made by 
rivers often lead to a meeting of the loops, so that a direct, 
new communication is established, and the course of the 
river is straightened out. The water takes, therefore, a 
more direct course to the sea. It cannot be said, however, 
to be of any advantage to the river to straighten its course. 
Again, a glacier moulds itself to its bed, and gradually 
moves around obstacles to a lower level, but this adaptation 
of the glacier to the form of its surroundings cannot be 
said to be of advantage to the glacier. On the contrary, 
the glacier reaches so much the sooner a lower level where 
it is melted. 
The unusual case of a solid being lighter than the liquid 
from which it forms, as seen in the case of ice, has been 
looked upon as a useful arrangement, since were the reverse 
the case all rivers and ponds would become solid in winter 
in cold climates, and the polar regions would become one 
solid block of ice. But no one will suppose for a moment 
that there is any relation between the anomalous condition 
of the lightness of ice, and its relation to the winter freezing 
of streams, ponds, etc. It has even been suggested that this 
property of ice was given to it in order that the animals 
