SPENCER 171 



the summer to rear a second and even a third brood. 

 Here, then, a higher degree of individuation receives 

 advantages so great as to more than compensate its 

 cost. It is not that the decline of genesis is less than 

 proportionate to the increase of individuation, but there 

 is no decline at all." l 



Spencer admits here that a bulkier organism should, 

 on his own theory, be less fertile than an organism of 

 less bulk. Obviously, then, if the formula is to be taken 

 literally, a well-nourished animal or bird should be less 

 fertile than one which is ill-nourished, since its greater 

 bulk represents a greater cost of individuation. He 

 admits that the larger blackbird is as fertile as or more 

 fertile than the linnet, and he meets this by arguing that 

 the increased cost of individuation in the blackbird is 

 more than compensated by an increased food supply. 

 In other words, he argues that the degree of fertility varies 

 directly with the surplus of nutrition over and above 

 the cost of individuation, thus changing his meaning to 

 suit the exigencies of the evidence. Spencer did not even 

 attempt to explain what factor determines the amount 

 of nutrition to be devoted to individuation and repro- 

 duction respectively, and to this omission much of the 

 confusion of thought is due. 



Considered as a generalisation covering the variation 

 in the potential degree of fertility as between species 

 and species, Spencer's formula is an inadequate expression 

 of the facts. If a species is to survive and evolve, its 

 degree of fertility must vary inversely with its capacity 

 for survival. The cost of individuation, which is measured 

 mainly by the bulk of the organism, is only one factor 

 making for survival, and by no means the most important. 



Neither the formula put forward by Spencer, nor the 

 one which we have seen expresses his real meaning, has 

 1 Principles oj Biology* Spencer, vol. ii, part vi. 



