48 HEREDITY AND SELECTION IN SOCIOLOGY 



relative strength of the elements of the germ-plasm is deter- 

 mined by this miniature struggle for the intragerminal nutritive 

 fluid. 



These alterations in the balance of the determinants in the 

 germ-plasm are the source of all hereditary variations. The 

 possibility of the adaptation of the organism Ues in the capacity 

 of the variations thus produced to continue indefinitely in a 

 given direction until " personal selection " intervenes. Altera- 

 tions in the balance of the determinants are thus responsible for 

 the increase, decrease, or variation of every part of the organism. 

 The reason why such variations in the composition of the germ- 

 plasm must necessarily continue in an ascendant direction until 

 personal selection intervenes, is that every alteration in the 

 balance of intragerminal nutrition to the advantage of one group 

 of determinants entails concurrently a weakening of another 

 group, at whose expense the first group will continue to increase 

 and develop. The victorious group wiU attract an ever greater 

 supply of nutritive matter, whereas the weaker group wiU have 

 its already lessened supply further diminished. This process 

 will continue until personal selection intervenes — that is to say, 

 until the variation caused by these changes in the germ-plasm 

 attains selective value, and becomes either useful or detrimental 

 to the life of the species. Should the variations be useful, personal 

 selection will favour its maintenance and subsequent increase 

 by favouring its possessors in the struggle for existence. Should 

 the variation be harmful to the life of the species, then personal 

 selection will eradicate it by the eUmination of those members 

 of the species who possess it. When the variation is useful to 

 the species, natural selection can ensure its further development ; 

 and artificial breeding, coming to the aid of natural selection, 

 may raise that variation to the highest possible point of perfec- 

 tion. Should the variation thus fostered be eventually developed 

 in a degree which renders it ultimately injurious to the species, 

 and inconsistent with the conditions of existence of that species, 



