SPENCER 167 



of aphides, for instance, as confirmation of his theory, 

 and sees no significance in the fact that asexual repro- 

 duction is favoured by abundant nutrition, whereas it 

 is scarcity that leads to sexual genesis. He entirely fails 

 to realise that the two methods of reproduction are adapted 

 to different conditions of life, acquire their full develop- 

 ment at different stages of evolution, are governed by 

 different principles, and usually react in diametrically 

 opposite fashion to the same conditions. 



Spencer also brings within the scope of his formula 

 the part played by instinct in reproduction. Genesis is 

 surrounded by a complex body of instinctive associations, 

 particularly in the case of the lower animals, which deter- 

 mine at what periods of the year and how often during 

 the year the species shall breed. These instincts are 

 hereditary and regulate the function of reproduction, so 

 that the young may be produced during the period of 

 the year most favourable to the species. Owing to the 

 varying length of the period of gestation, it is necessary 

 that coupling should take place at different periods of 

 the year among different species. It is useless to attempt 

 to explain these instincts by a simple physiological re- 

 action, as some species couple in summer and some in 

 winter, some during the season of plenty and some during 

 the season of scarcity, the time being determined, not 

 by the conditions of the moment, but by the necessity 

 of producing the young at certain favourable periods of 

 the year, and instinct is the guide. 



The theory of Spencer is that the degree of fertility varies 

 inversely with the cost of individuation. It is a curious 

 fact that the literal meaning of this formula is the reverse of 

 that put upon it by Spencer himself. For Spencer assumes 

 that on his hypothesis a well-fed organism will be more 

 fertile than an ill-fed organism. But surely the amount 

 devoted to individuation is greater in a well-nourished 



