A RETROSPECT 483 



are too slow for him, he rebels against her deliberation. 

 Man exterminates an animal : he slays rashly, rapidly, re- 

 morselessly, and, the deed done, takes time to regret his 

 impetuosity. Nature, it would seem, considers well before 

 she deals the final blow; Man deals the final blow and then 

 considers. 



With the introduction of animals, it is as* with their 

 extermination the same coarse handling marks Man's ways. 

 Nature introduces, say, a new molluscan shell-fish to our 

 fresh waters. A single egg, no bigger than a pinhead, or 

 perhaps a dozen mixed with the clay attached to the foot of 

 a migrating duck, form the possible foundation of a colony. 

 But the colony is so small that, the newcomer creates no 

 violent revolution in its surroundings. It may die out under 

 competition, leaving no trace; it may increase and in the 

 end choke its neighbour's life, but the latter process is 

 generally a slow one, there is no fierce apparent struggle, 

 ajid, besides, with the gradual increase of the newcomer, 

 fresh foes develop which tend to keep it in check. 



How different when man interferes! He introduces a 

 new mollusc: he dumps basketsfull time and again at the 

 same spot, upsetting the balance of life in the neighbour- 

 hood, offering the newcomer, if conditions be suitable, 

 chances of increase, which may cause the countryside to be 

 overrun before a natural enemy arises to keep the alien 

 within bounds. 



Even his unforeseen and accidental introductions have 

 the same effect, for the persistence with which the same 

 pest is introduced time and again, in timber or food, with 

 plants or fruit, makes sure that, unless conditions are actively 

 hostile, it will at one time or another set down its foot and 

 become an established guest. 



MAIN TRENDS OF MAN'S INFLUENCE 



Along three broad lines man's influence has played upon 

 the animal world. On one hand it has tended to reduce the 

 numbers of one set of animals, to limit their range and to 

 exterminate them ; on the other hand it has leaned towards 

 increasing the numbers of another set of animals, compelling 

 them to enter fresh areas, which often enough they have 



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