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 



