r 



TWO OBJECTIONS CONSIDERED 



tory deals with, a quite similar process goes on. 

 First we may note, with Mr. Darwin, that " as 

 the species of the same genus usually have, 

 though by no means invariably, much similarity 

 in habits and constitution, and always in struc- 

 ture, the struggle will generally be more severe 

 between them, if they come into competition 

 with each other, than between the species of 

 distinct genera. We see this in the recent ex- 

 tension over parts of the United States of one 

 species of swallow having caused the decrease 

 of another species. The recent increase of the 

 missel-thrush in parts of Scotland has caused the 

 decrease of the song-thrush. How frequently 

 we hear of one species of rat taking the place 

 of another species under the most different cli- 

 mates ! In Russia the small Asiatic cockroach 

 has everywhere driven before it its great con- 

 gener. In Australia the imported hive-bee is 

 rapidly exterminating the small stingless native 

 bee. One species of charlock has been known 

 to supplant another species ; and so in other 

 cases. We can dimly see why the competition 

 should be most severe between allied forms, 

 which fill nearly the same place in the economy 

 of nature ; but probably in no one case could 

 we precisely say why one species has been vic- 

 torious over another in the great battle of 

 life." 1 



^ Origin of Species, 6th edition, p. 59. 



51 



