THE ORIGIN OF SPECIES BY NATURAL SELECTION. 7 



an improvement as shall enable it to survive its cotemporarics 

 in the ' struggle for life.' But it turns out to be the very- 

 reverse of this. Plants and animals may gain in those 

 qualities which make them most useful or agreeable to man, 

 but they lose those properties which enable them best to 

 maintain the struggle for life. Our poultry lose, for the most 

 part, the power of flight- The domestic ass, when Avell cared 

 for, increases in size, but no longer possesses the fleetness of 

 the ass of the desert. The jungle fowl of India is a small 

 bird, but vigilant, shy, and powerful of wing ; while the 

 domestic bird is large, heavy, and dull, and, if turned into the 

 woods of its native country, would unquestionably perish from 

 incapacity of feedmg and defending itself. 



Mr. Darwin has given special attention to the breeding of 

 the blue rock pigeon, the only species of its numerous family 

 which is amenable to domestication, and which sports into 

 varieties. These varieties seem to be indefinite in their 

 amount, for besides the more usual sorts, distinguished chiefly 

 by colour, we have such varieties as tumblers, runts, fantails, 

 barbs, pouters, and carriers. Not one of these can be said to 

 have any superior advantage over the wild blue pigeon in so 

 far as regards capacity to maintain the struggle for life, and 

 some of them are of such defective formation that they would 

 surely perish were man's care ^vithdrawn. Moreover, the 

 varieties produced by domestication are not permanently 

 profitable to the individual, as the progressive theory would 

 have us to understand; for it has been ascertained that when 

 the common house pigeon joins the wild birds its peculi- 

 arities are, in a short time, absorbed in the mass of the pri- 

 mitive stock ; whereas, had the variation been advantageous, 

 it ought, according to the theory, to have been heritable, 

 displacing the wild bird. 



It is the same with cultivated plants as with domesticated 

 animals ; they gain in size and acquire properties useful or 

 agreeable to man, but they lose in capacity to maintahi the 

 struggle for existence. Some of them, such as the cultivated 



