170 THE LAW OF BIRTHS AND DEATHS 



bulky organisms as the horse or the elephant, we can 

 perceive that Spencer's formula is a rough but inadequate 

 expression of the broad results of organic evolution. The 

 bigger the organism the less, as a rule, will its fertility 

 be. But it is quite inadequate as an expression of the 

 facts, 1 as a few simple illustrations will show. " The 

 condor lays a couple of eggs and the ostrich a score, and 

 yet in the same country the condor may be the more 

 numerous of the two ; the fulmar petrel lays but one egg, 

 yet it is believed to be the most numerous bird in the 

 world. One fly deposits hundreds of eggs, and another, like 

 the Hippobosca, a single one. ' ' 2 Compare also the difference 

 between the fertility of the wild pigeon and the pheasant. 



The formula has no application to the variation of the 

 degree of fertility under the direct influence of the environ- 

 ment. The minimum amount necessary to sustain the 

 organism would be a fairly constant quantity throughout 

 life after maturity. Therefore there could be no inverse 

 ratio, since there would be little or no variation. While, 

 if we assume the phrase " cost of individuation " to 

 apply to the gross quantity of nutriment assimilated by 

 the organism, then the meaning of the formula would 

 be the reverse of that put upon it by Spencer. 



Throughout Spencer's argument his meaning is ex- 

 tremely nebulous, and varies constantly to suit the exi- 

 gencies of the evidence. The following passage illustrates 

 this, and shows also that the above explanation of his 

 real meaning is correct. " Thus the strength of the 

 blackbird opens to it a store of good food much of which 

 is inaccessible to so small and weak a bird as a linnet, 

 a store especially helpful to it during the cold months 

 when the hibernating snails in hedge bottoms yield it 

 abundant provision. The result is that the blackbird is 

 ready to breed very early in the spring, and is able during 



1 See p. 38. a Origin of Species. Darwin, chap. iii. 



