Hillside. 149 



can be no doubt that Nature would at once seize hold of 

 them, and work on the tendency to vary in the desired 

 direction so far as was necessary for the most complete well- 

 being of the animal under its new conditions of existence. 



The work of Nature, however, is generally slow, so slow 

 indeed that a natural change of environment may not take 

 place for a vast number of years. We must bear in mind, 

 however, that such a change may take place suddenly, 

 brought about perhaps by some natural force, or, still more 

 probably, by the interference of man. Sudden changes, how- 

 ever, so far as they are the result of natural forces, are 

 unusual, and we may look upon the axiom, " Natura non 

 facit saltum," as indicating the method in which her work 

 is usually done. When, however, a change of environment 

 does take place, whether it be small or great, those indi- 

 viduals which are unable to adapt themselves to the altered 

 conditions of existence soon die out, whilst those which are 

 able to do so are preserved, and transmit to their offspring 

 the peculiarities to which they owe their preservation. We 

 can then readily understand how it is that that form which 

 is best suited to its surroundings is finally established ; but 

 long, long before it reached its present state of excellence or 

 fitness, it had its variable characters modified and moulded 

 in such directions as proved to be of advantage to it, and 

 this moulding has always been, and even now is, in 

 progress. 



As an illustration of natural selection acting over a long 

 period, we may take our common rabbit, of which those in- 

 dividuals with the keenest sense of hearing and the greatest 

 speed would stand the best chance of being and have been 

 preserved. Again, the antalopes, which are so severely 



