I02 THE MEANING OF EVOLUTION 



groiincl wilhuut any special protection. As we rise 

 in the scale of the bird world we find nests provided 

 for the eggs. 1 hese nests become increasingly com- 

 plex: and specialized, until we reach the oriole's home 

 with its wonderfully woven mass of fiber, which, in 

 spite of its apparent looseness, supports well the 

 weight of the mother bird and of her eggs. The 

 robin, not content with making a woven basket, plas- 

 ters it with clay, and makes an absolutely impervious 

 nest. 



When we remember that both mammals and birds 

 are the modern descendants of cold and scaly reptiles 

 of an earlier geological time, it becomes interesting to 

 compare their clothing. Evidently in the mammals 

 hairs began to come out between the scales. Gradu- 

 ally the scales became fewer and the hairs more abun- 

 dant until finally the scales have all disappeared, ex- 

 cept those that remain as the claws on the toes. The 

 ancestors of the birds, on the other hand, boldly trans- 

 formed their scales into feathers. 



Another need for shelter arises in connection with 

 the approach of winter. This problem of withstand- 

 ing the cold season is complicated by the presence of 

 two new factors. First and most directly, the cold 

 itself is a distinct obstacle to the comfort of many of 

 these creatures ; as a secondary result of this cold, the 

 food of many animals disappears entirely in winter. 



