PRACTICAL IMPORTANCE OF ZOOLOGY 13 



to Australia increased at such a rate as to make pasturage 

 well-nigh impossible, so that an enormous sum of money has 

 now to be spent annually in order to keep it in check. 



Now these facts have a double interest for us. First, 

 civilised man for his own use insists on rearing enormous 

 herds of a few kinds of domesticated animals and enormous 

 crops of a few species of cultivated plants. Such thickly 

 massed crowds of individuals belonging to a single species are 

 rare in Nature, and are as stubble to the flame if once invaded 

 by a successful enemy. If an enemy like the boll-weevil gains 

 an entrance to his cotton-fields, how shall man protect himself 

 against it? The answer which one of the best living ento- 

 mologists gives to this question is as follows : " The only way 

 in which a problem of this kind can be attacked is by a careful 

 study of the habits and life-history of the insect enemy ; such 

 a study will be sure to reveal some weak point in the armour 

 of the foe, and it is there that we must attack him." A know- 

 ledge of zoology is essential, therefore, for the proper protection 

 of our crops and herds, and indeed how could it be otherwise 1 

 Are not we ourselves a species of animals maintaining our 

 right to existence by a hard struggle against our competitors *? 

 And it may be added that these competitors are just as ready 

 to attack our own bodies as they are to devour our domesticated 

 animals and plants. Some of them, which have accustomed 

 themselves to live in our blood, run riot there and bring pain 

 and death in their train. Only by a careful study of their life- 

 history is it possible for us to guard ourselves against them. 

 By means of such studies the American biologists have made 

 the Isthmus of Panama, once a graveyard for Europeans, one 

 of the healthiest districts in America. 



The second interest which the competition between species 

 has for the thoughtful man is its bearing on the history of the 

 human race itself. There is no doubt that for tens of 

 thousands of years the numbers of mankind were kept down 

 by internal and external enemies, just as are the numbers of 

 the oyster-catcher. But in the last two thousand years, and 

 more notably in the last two hundred, and most notably of all 

 in the last fifty, man has been learning to know and conquer 

 his enemies. The result of this has been that population 

 amongst civilised nations has begun to increase at an alarming 



