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diminislied opportunity for crossing with the best fitted ; and so 

 on through the different grades of fitness, the power to affect the 

 next generation through having a share in propagating will 

 measure the power to aff'ect the progeny of the best fitted by 

 crossing with them. It therefore follows that the freest cross- 

 ing of the fittest is with the fittest. 



Natural Selection therefore proves to he a process in which 

 the fittest are prevented from crossing loith the less fitted through 

 the exclusion of the less fitted, in proportion to their lack of fitness. 

 Through the premature death of the least fitted, and the inferior 

 propagation of the less fitted, there arises a continual prevention 

 of crossing between the less fitted and the better fitted ; and 

 without this separation the transforming influence of the laws 

 of organic life would have no power to operate. As Darwin 

 has pointed out, the results produced by this removal of the 

 less fitted and separate propagation of the better fitted, closely 

 correspond with those produced by the breeder, who kills off* the 

 less desirable individuals of his stock before they have opportunity 

 to breed. The selection of the breeder avails nothing unless it 

 leads to the determining of the kind that shall breed ; and this 

 he cannot accomplish without preventing free crossing with those 

 that he does not desire. He must use some method to secure 

 the separate breeding of the form that he desires to propagate. 

 "We therefore find in both Natural and Artificial Selection the 

 same fundamental method. In either case, the kind that is to 

 propagate is determined by the selection, and those that are 

 not to propagate are in some way excluded. The process may 

 therefore be called the exclusive breeding of certain kinds ; and 

 Natural Selection may be defined as the exclusive breeding of 

 those hetter adapted to the environment. 



But if from one stock of horses we wish to develop two distinct 

 breeds, one of which shall excel in fleetness, and the other in 

 strength for carrying or drawing burdens, the result will not be 

 gained by simply preventing all that are inferior in strength or 

 fleetness from breeding. By this process, which is tlie Exclusive 

 Breeding of the desired kinds, we should obtain one breed with 

 fair powers of strength and fleetness ; but the highest results 

 in either respect would not be gained. Such experiments show 

 that the Exclusive Breeding of other than average forms causes 

 Monotypic Evolution, and that to secure Divergent or Polytypic 

 Evolution some other principle must he introduced. 



