220 SELECTION. Chap. XXI. 



favourable for the work"; and difficulty in pairing, as with 

 cats, prevents the formation of distinct breeds. On nearly 

 the same principle the cattle of the small island of Jersey 

 have been improved in their milking qualities " with a 

 rapidity that could not have been obtained in a widely 

 extended country like France." 41 Although free crossing 

 is a danger on the one side which every one can see, too close 

 interbreeding is a hidden danger on the other side. Un- 

 favourable conditions of life overrule the power of selection. 

 Our improved heavy breeds of cattle and sheep could not 

 have been formed on mountainous pastures ; nor could dray- 

 horses have been raised on a barren and inhospitable land, 

 such as the Falkland Islands, where even the light horses of 

 La Plata rapidly decrease in size. It seems impossible to 

 preserve several English breeds of sheep in France ; for as 

 soon as the lambs are weaned their vigour decays as the heat 

 of the summer increases : 42 it would be impossible to give 

 great length of wool to sheep within the tropics ; yet 

 selection has kept the Merino breed nearly true under diver- 

 sified and unfavourable conditions. The power of selection 

 is so great, that breeds of the dog, sheep, and poultry, of the 

 largest and smallest size, long and short beaked pigeons, and 

 other breeds with opposite characters, have had their charac- 

 teristic qualities augmented, though treated in every way 

 alike, being exposed to the same climate and fed on the same 

 food. Selection, however, is either checked or favoured by 

 the effects of use or habit. Our wonderfully-improved pigs 

 could never have been formed if they had been forced to 

 search for their own food ; the English race-horse and grey- 

 hound could not have been improved up to their present high 

 standard of excellence without constant training. 



As conspicuous deviations of structure occur rarely, the 

 improvement of each breed is generally the result of the 

 selection of slight individual differences. Hence the closest 

 attention, the sharpest powers of observation, and indomitable 

 perseverance, are indispensable. It is, also, highly important 



41 Col. Le Couteur, ' Journal Roy. Agricult. Soc.,' vol. xiv., 1853, pp. 215, 

 Agricult. Soc.,' vol. iv. p. 43. '217. 



i2 Malingie - Nouul, Journal R. 



