THE EFFECT OF MA\ 555 



on insufficient knowledge of the ecological problems involved, and more 

 especially when there is an indescriminate broadcasting of poisons. 



The destruction and extinction of many races of mankind have 

 gone hand in hand with the spread of the civilized peoples. The com- 

 plete extermination of the original inhabitants of Tasmania, the prob- 

 lem of whose racial affinities was scarcely understood before they had 

 vanished forever, may be recalled as the most flagrant example of this 

 phase of destructiveness. 



More recently man has turned his attention to the eradication of 

 disease-producing organisms and of their carriers. None of these at- 

 tempts has been completely successful, but the campaign against the 

 organisms producing yellow fever and the Aedes mosquito carrying 

 them has been sufficiently successful on a geographic scale so that 

 temperate and subtropical areas are now exempted from this plague, 

 and the organisms producing the disease are being hunted in their 

 tropical lairs as relentlessly as ivory collectors ever hunted elephants 

 for profit. Local successes have been won, as for example in the 

 Canal Zone in Panama, in the similar struggle against the malarial 

 parasite by attacking its bearer, the Anopheles mosquito, and by keep- 

 ing these mosquitoes from biting infected persons. In this warfare, 

 tropical, mosquito-eating fishes are annually introduced into northern 

 waters where they are annually winter-killed, but where they do give 

 partial relief from the mosquito plagues of the summer. 



The most effective control measures have been those which de- 

 stroy the breeding grounds of the harmful species, just as, in general, 

 the activities of man which have left the breeding places intact have 

 not led to the extermination of the desirable animals associated with 

 him. The reduction in numbers in the face of a spreading civiliza- 

 tion has usually kept pace with the reduction in suitable breeding 

 niches, and conversely, where man's activities have increased breeding 

 habitats, then the other members of the community have increased in 

 numbers of individuals and, if the niches are varied, in number of 

 species as well. 



So great have been the changes in the vegetation and animal life 

 of the world with the spread of civilized man, that over wide areas 

 the natural phenomena of geographic zoology and of ecology in gen- 

 eral are completely secondary, approachable from the agricultural or 

 economic standpoint rather than from the biological. The importance 

 of the study of the conditions of life, undisturbed by the gross effects 

 of civilization, has been increasingly appreciated in recent years. The 

 only hope for the preservation of natural conditions for the future, 

 in temperate latitudes, and probably in the tropics as well, 24 lies in 



