Chap XXlIL CONDITIONS OF LIFE. 261 



variation to make a sound classification. The action of 

 changed conditions, whether leading to definite or indefinite 

 results, is a totally distinct consideration from the effects of 

 selection ; for selection depends on the preservation by man 

 uf certain individuals, or on their survival under various and 

 complex natural circumstances, and has no relation whatever 

 to the primary cause of each particular variation. 



I will first give in detail all the .facts which I have been 

 able to collect, rendering it probable that climate, food, &c, 

 have acted so definitely and powerfully on the organisation of 

 our domesticated productions, that new sub-varieties or races 

 have been thus formed without the aid of selection by man or 

 nature. I will then give the facts and considerations opposed 

 to this conclusion, and finally we will weigh, as fairly as we 

 can, the evidence on both sides. 



When we reflect that distinct races of almost all our domes- 

 ticated animals exist in each kingdom of Europe, and formerly 

 even in each district of England, we are at first strongly 

 inclined to attribute their origin to the definite action of the 

 physical conditions of each country; and this has been the 

 conclusion of many authors. But we should bear in mind 

 that man annually has to choose which animals shall be pre- 

 served for breeding, and which shall be slaughtered. We 

 have also seen that both methodical and unconscious selection 

 were formerly practised, and are now occasionally practised 

 by the most barbarous races, to a much greater extent than 

 might have been anticipated. Hence it is difficult to judge 

 how far differences in the conditions between, for instance, 

 the several districts in England, have sufficed to modify the 

 breeds which have been reared in each. It may be argued 

 that, as numerous wild animals and plants have ranged 

 during many ages throughout Great Britain, and still retain 

 the same character, the difference in conditions between the 

 several districts could not have modified in a marked manner 

 the various native races of cattle, sheep, pigs, and horses. 

 The same difficulty of distinguishing between the effects of 

 natural selection and the definite action of external conditions 

 is encountered in a still higher degree when we compare closely 

 allied species inhabiting two countries, such as North America 



