The Making of Species 



It is thus conceivable that, in a brood consist- 

 ing of several individuals, a particular molecule 

 or set of molecules in one of the individuals may 

 receive more than its share of nourishment, and 

 this will result in the organs of that individual 

 which spring from the well-nourished molecules 

 being exceptionally well developed. Thus arises 

 the phenomenon of differences between the 

 members of a litter or brood. 



Natural selection will tend to eliminate those 

 individuals in which the resulting variation is an 

 unfavourable one. If the environment is such, 

 as in the case of an internal parasite, that the 

 production of germ cells is the most necessary 

 function of the organism, then those individuals 

 in which the germ-forming molecules increase at 

 the expense of the body-forming ones will tend 

 to be preserved. This would cause the pheno- 

 menon which biologists term degeneration. 

 The nourishment of the various biological 

 molecules may possibly depend on their relative 

 positions in the egg. Those in a favourable 

 position will then tend to develop at the expense 

 of the others. This will result in variation along 

 definite lines. Each succeeding generation will 

 tend to an increased development of that par- 

 ticular organ to which the favourably-situated 

 molecule gives rise. This process may continue, 

 as in the case of the horns of the Irish elk, until 

 the development of that particular organ becomes 



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