102 THE MEANING OF EVOLUTION 
ground without any special protection. As we rise 
in the scale of the bird world we find nests provided 
for the eggs. These 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. 
