THE OKKUN AND TlIK KXTINOTION OF SI'KCl KS 361 



St. Heleiii). Tlu> (M-iniiuil and rcniarkuble I'auiiii and iiora (if this 

 island l\ad for the most part disappcai-od aoo yeui's aij,x), lhrt)iigli the 

 enttinu- down of trees in the l\)i-ests, and these were later wiiolly 

 destroyed hy the introduction of _i;oats, which devoured all the ^'ouny 

 trees as they m-ew. Hut with tlie forests most of the indiffcnous 

 insects and birds were doomed to destruction, so that now there is 

 not an indigenous bird or buttertlj' to he found there; only a few 

 terrestrial snails and beetles of tlie original fauna still survive. 



Hut it is not only on islands that a large number of species ha\e 

 been decimated or entirely exterminated by deforestation, by the 

 introduction of plants cultivated by man and of the 'weeds' 

 associated with these, and by the importation of dom-esticated animals. 

 In Central Europe not only have all the larger beasts of prey, like 

 the bear, the lynx, and the wolf, almost completely disajipeared, but 

 the reindeer, the bison, the wild o\ (Aurochs), and the elk have been 

 extei-niinated as wild animais, and in North America the buffalo will 

 soon only exist in preserved herds, if that is not already the casi'. Here, 

 of course, the direct interference of the all-too-powerful enemy, man, 

 has played the largest part in causing the disappearance of the species 

 referred to, but the process may give us an idea of the wa}* in which a 

 superior animal enemy may be able giadually to exterminate a weaker 

 sjiccies where there is no attainable or even conceivable variation 

 which might preserve them from such a fate. Several of the maunnals 

 wliich 1 have mentioned are not yet entirely exterminated ; even the 

 -Vurochs perhaps still exists in the pure white herds preserved in 

 some British parks ; but there are more instances than that of the 

 Dodo of the utter extermination of a species through human agency 

 within historic times. It niay be doubtful whether the sea-otter 

 {I'JiiJiydris marina) has not been already quite exterminated because 

 of its precious fur, but it is quite certain that the huge sea-cow 

 (h'Jiilfi nil t-telleri), which lived in large numbers in the Behring Straits 

 at the end of the eighteenth and the beginning of the nineteenth 

 centuries, was completely exterminated by sailors within a few 

 decades. 



We may therefore gain from what is going on before our eyes, 

 so to speak, some sort of idea of the way in Mhich the extermination 

 of species may go on even independently of man at the present time, 

 and how it unist ha\e gone on also in past ages of the earth's histoiy. 

 Migrations of species have taken pliice ceaselessly, although very 

 slowly, for every species is endeavouring slowly to extend its range 

 and to take posstvssion of new territories, and thus the fauna and 

 flora of any region must have changed in the course of time, new 



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