168 THE LAW OF BIRTHS AND DEATHS 



organism than in one that is ill-nourished. Therefore, 

 if the degree of fertility is to bear an inverse proportion 

 to the cost of individuation, a well-nourished organism, 

 whose individuation has cost more, should be less fertile. 



The formula is put forward as an explanation of the 

 law which governs fertility. We must, therefore, take it 

 that the amount of nutrition devoted to individuation 

 determines what amount shall be devoted to reproduction, 

 and not vice versa ; for in the latter case the law govern- 

 ing fertility would remain unexplained. Therefore a well- 

 nourished organism representing a higher cost of indi- 

 viduation should show a lower degree of fertility. 



The fact is that Spencer had not accurately grasped the 

 meaning of his own formula, or rather had not correctly 

 formulated his own meaning. Although he puts forward 

 the proposition that the degree of fertility will vary in- 

 versely with the cost of individuation, yet throughout his 

 argument he really means and endeavours to prove that 

 the degree of fertility will vary directly with the surplus 

 of nutrition over and above the cost of individuation. 

 These propositions are wholly different. Spencer con- 

 founded the two. The inverse ratio between fertility 

 and the cost of individuation may be shown thus : 



I Amount devoted to I Amount devoted to 

 individuation. reproduction. 

 d I I i ! 



! 



Amount of nutrition available a constant quantity. 



It will be noted that the above diagram, as is the case 

 with Spencer's formula, assumes the amount of nutrition 

 available to be a constant quantity. On this assumption 

 the amount devoted to reproduction must necessarily 

 decrease as the amount devoted to individuation increases. 

 As the formula purports to be an explanation of the law 

 governing fertility, the amount devoted to individuation 



