I06 DARWINISM AND THE PROBLEMS OF LIFE 



and as fresh arrivals from the south came In later years 

 of famine, the place was again too small, and they had 

 to spread in all directions, including the north. 



Could the spread towards the north proceed 

 indefinitely? No; because the time came when the 

 wanderers had passed the winter-limit. When the cold 

 season broke on them, the earth became covered with 

 snow, the streams froze, and famine set in again. 

 What happened to the poor birds? Those that 

 remained, waiting for better days, were destroyed, as 

 the lack of food lasted longer than they could endure ; 

 others, that fled to the north, east, or west, found the 

 same conditions everywhere and perished also ; only 

 those were saved that remembered their origin and the 

 land of eternal summer, and returned southwards. 



We may confidently assume that these little creatures, 

 barely escaping from death, would not at once return to 

 the north. But natural selection — for it is with this 

 we have to deal — is inexorable. The birds were back 

 in fully populated lands, and when the nesting - time 

 came in spring there was no room for them ; we know 

 that most birds require a certain area for nesting, and 

 will suffer no others of the same species within that 

 area. The wood-pecker, for instance, and a great 

 number of others, including our gentle robin, act in this 

 way. What happened to these birds that had become 

 strangers in their old home ? Many of them failed to 

 breed ; these were the most timorous who would not 

 return to the north, and died out through leaving no 

 offspring. But there would certainly be bolder ones 

 here and there, who would remember how they had 



