xni EXTENSIONS OF DARWINISM 273 



more vigorous determinants will lead to more vigorous 

 growth of the special part or organ they determine hair, 

 horns, ornaments, etc., and wherever this increase is useful, 

 or even not hurtful, to the species, it will go on increasing, 

 generation after generation, by the survival of more and 

 more vigorous determinants. 



There is therefore both an internal and an external 

 struggle for existence affecting all the special parts organs, 

 ornaments, etc. of every living thing. With regard to the 

 more important structures, such as the limbs, the organs of 

 vision and hearing, the teeth, stomach, heart, lungs, etc., on 

 which the very existence of the individual as well as of the 

 species depends, survival of the fittest in due co-ordination 

 with all other parts of the body will continually check any 

 tendency to unbalanced development, and thus, generation 

 by generation, suppress the tendency of the more vigorous 

 determinants to increase the growth and vigour of its special 

 determinates, by elimination of the individuals which exhibit 

 such unbalanced growth. But in the case of appendages, 

 ornaments, or brilliant colours, which may begin as a mere 

 outlet for superfluous vital energy in dominant races, and 

 then be selected and utilised for purposes of recognition, 

 warning, imitative concealment, or for combat among males, 

 there will not be the same danger to the very existence of 

 the adult animal. It will, however, often happen that the 

 increase through germinal selection will continue beyond 

 the point of absolute utility to the individual ; between 

 which and the point of effective hurtfulness there may be a 

 considerable margin. In this way we have a quite intelligible 

 explanation of the enormous development of feathers or 

 decorative plumes in so many birds, enormous horns in deer 

 and antelopes, huge tusks in elephants, and huge canine 

 teeth in other quadrupeds. This view is supported by the 

 suggestive fact, that many of these appendages are retained 

 only for a short period, during the breeding season, when 

 vigour is greatest and food most abundant, and when 

 therefore they are least injurious. 



Again, when acting in an opposite direction, the theory 

 serves to explain the rapid dwindling and final disappearance 

 of some useless organs, which mere disuse is hardly sufficient 



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