DISTRIBUTION OF AUSTRALIAN FAUNA. 449 



One of the most interesting and remarkable aspects of the 

 order of nature is that which presents it to us as a multitude of 

 potentially destructive agencies so operating ujDon each other that 

 the interests of each individual species are safeguarded by the 

 ravages of the rest. We watch some beautiful butterfly fanning 

 its wings to the sun on a summer's day, and we perhaps forget while 

 we admire its glorious colors that if its species were able to increase 

 and multiply to the full extent of its natural powers of reproduc- 

 tion for a few years it might possibly destroy the human race l)y 

 depriving it of an essential article of food. Man's direct power of 

 checking the natural increase of a butterfly is very small indeed. 

 But there are other forms of life whose destructive powers are 

 naturally exercised upon the butterfly, and it is owing to their 

 operations that the butterfly is an object of admiration and not an 

 instrument of ruin ; and siniilarly throughout the whole economy of 

 nature everything is in itself selfish and destructive, but the 

 selfishness and destructiveness of each species is neutralised by the 

 similar qualities of some other species, generally of many other 

 species. Now it follows from this — from this beautiful balancing 

 of the powers of the different forms of life — that when a species 

 perishes the reason riiay be a very remote one, may be simply that 

 something iias occurred to remove (perhaps by an intricate chain 

 of cause and effect) a check from interfering with the increase 

 of something that is destructive to it. Mail's powers are so out 

 of proportion to the powers of all other living things that he 

 seems likely on a priori grounds to habitually produce such a 

 disturbance of the harmony of nature. For some reason or other 

 he thinks it desirable to wage war on a plant or an animal and to 

 greatly redvice its numbers. It is impossible to say what injury he 

 may be inflicting on some of his interests that he has not regarded 

 as concerned in the matter at all by diminishing some force in 

 nature that it may be tends to keep in check some other force that 

 is hostile to those particular interests. 



Among all the means that man can employ for disturbing the 

 order of nature there is perhaps none more likely to produce large 

 results than that of introducing into the fauna of a particular 

 region some species that is not indigenous to it. An introduced 

 species is perhaps in its nature unfavorable to something that is 

 already there, and so increases the difficulties of life to that of 

 which it is an enemy. It is perhaps capable of increasing the 

 possibilities of multiplication to sonae indiffenous species, and so 

 causes it to assume an importance in the economy of nature that it 

 had not previously possessed. It is often probably due almost 

 entirely to the immigratinn of species — very often deliberately 

 caused by man — that some species become what we call pests ; 

 and where that is not the cause the cause is often to be found in 

 the fact that man has thought fit to destroy something whose 

 destruction has removed a check that had previously limited the 

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