ORGANIC EVOLUTION — THE FACTOKS 113 



differences between the individuals are explainable only 

 on the theory that they are due to inborn variations. The 

 extent to which the individuals of a nest or litter differ 

 in powers and qualities is often quite remarkable, and 

 in no respect is this difference more remarkable than in 

 fighting power. This power in dogs and fowls, as in 

 the moose, depends on an immense number of structures, 

 in fact, on almost all the structures of the body, and 

 therefore, when one of a litter or brood exhibits a 

 marked superiority over his brothers in fighting power, 

 we must suppose that his suj)eriority results from a 

 favourable co-adaptive development, due to inborn 

 variations alone, of all the structures concerned in 

 fighting. Now if the ability to secure mates, and 

 therefore descendants, depends largely on the fighting 

 power, as it actually does among so many wild creatures, 

 including the canida3, the gallinacei, and the cervidos, 

 are not the differences due to inborn variations alone, 

 which, as we have seen, are considerable, sufficient to 

 , lead, by survival of the fittest, to the evolution of the 

 fighting power, i. e. to the co-adaptive evolution of all 

 the co-ordinate structures on which that power depends ? 

 Would a race descended from the best fighters in each 

 litter or brood differ from a race not so descended, from 

 a race as regards which nature has exercised no selection 

 in this respect ? I suppose that uo one would maintain 

 that it would not differ, for to maintain such a proposi- 

 tion would be to maintain that a race descended from the 

 biwccest and strongest individuals alone Avould not differ 

 from a race the ancestry of which included smaller and 

 weaker individuals. Yet here we would have just such 

 a case of co-adaptive evolution resulting from the 

 accumulation of inborn variations alone, and involving 

 nearly all the structures in the body, as Mr. Spencer 

 has declared is impossible. 



A thousand similar examples can be found. For 



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