EVOLUTION AS A NATURAL PROCESS 141 



without reference to animals like the rabbit. When 

 the first of these were introduced they found a territory 

 without natural enemies where everything was favor- 

 able, They promptly multiplied so rapidly that within 

 a few years their descendants were numerous enough to 

 eat up practically every green thing they could reach. 

 Two decades ago, the single province of Queensland was 

 forced to expend $85,000,000 in a vain effort to put 

 down the rabbit plague. The remarkable statement has 

 been made that in some places nature has taken a hand 

 in causing a new type of rabbit to evolve. Finding the 

 situation desperate, some of the animals have begun 

 to develop into tree-climbing creatures. The animals 

 exist in such numbers that the available food upon the 

 ground is insufficient for all, and so some elimination 

 results. But the young rabbits with longer claws, 

 varying in this way on account of congenital factors, 

 have an advantage over their fellows because they 

 can climb some of the trees and so obtain food inac- 

 cessible to the others. If the facts are correctly 

 reported, and if the process of selection on the basis 

 of longer claws and the climbing habit is continued, 

 the original type of animal is splitting up into a form 

 that will remain the same and live upon the ground, 

 and another that will be to all intents and purposes 

 a counterpart of our familiar squirrel. All the evi- 

 dence goes to show that squirrels have evolved from 

 terrestrial rodents; if the data relating to Australian 

 rabbits are correct, nature is again producing a 

 squirrel-like animal by evolution in a region where 

 the former natural situation has been interfered with 

 by man. 



