98 THE MEANING OF EVOLUTION 
specializations for food getting. For instance, primi- 
tive mammals have little pointed teeth which fit them 
for feeding on insects. In each of the great order of 
mammals a special development of these teeth has 
occurred. Among the rodents or gnawing animals 
the front teeth have become long and chisel-shaped 
for nibbling. The horse has formed them for nip- 
ping, and his hind teeth for grinding. In the dog 
the teeth near the front have become long for tearing 
his flesh food, while his hind teeth, working with the 
motion of scissors, cut it into pieces. 
A second great class of specialization is seen in 
the changes of habit that provide the animal with 
shelter. The home seems so necessary a part of hu- 
man life that it is almost impossible to think of an 
animal having nothing that in the faintest degree 
could be called a home. We at least expect it to have 
some sheltered place in which it passes most of its 
time and to which it returns after its wanderings. 
The great majority of all animals have no such home. 
The place in which we find them to-day may not be 
the place in which they will be to-morrow. All places 
are alike to them. The ordinary conduct of their 
daily life drives them about in the search for food. 
Their attempt to escape from their enemies leads them 
each day into new situations, and they may, and prob- 
ably do, have no power to recognize the old location if 
