



272 DEFINITE ACTION OF THE Chap. XXIII. 



following chapter. We know, however, far too little of the 

 causes and laws of variation to make a sound classification. 

 The direct action of the conditions of life, whether leading to 

 definite or indefinite results, is a totally distinct consideration 

 from the effects of natural selection ; for natural selection 

 depends on the survival under various and complex circum- 

 stances of the best-fitted individuals, but has no relation 

 whatever to the primary cause of any modification of structure. 



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 domesti- 

 cated productions, that they have sufficed to form new sub- 

 varieties or races, without the aid of selection by man or of 

 natural selection. 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- 



ved 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 very difficult to judge how far 

 the difference in conditions between, for instance, the several dis- 

 tricts in England, could have sufficed without the aid of selection 

 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 so marked a 

 manner the various native races of cattle, sheep, pigs, and 

 horses. The same difficulty of distinguishing between selection 

 and the definite effects of the conditions of life, is encountered in 

 a still higher degree when we compare closely allied natural 



