72 THE LAW OF BIRTHS AND DEATHS 



of these valuable animals by breeding from the more 

 fertile rather than from the less fertile individuals. Even 

 when individual merit is of more importance than numbers, 

 the chances of obtaining a good specimen are obviously 

 greater in a large than in a small litter. To this day 

 fanciers who have to pay a large stud fee for the services 

 of the best males will, as far as possible, use only females 

 of proved fertility. If the litter is a small one, the chances 

 of obtaining a good specimen are correspondingly small. 

 If, on the other hand, the litter is a large one, the chances 

 of obtaining a good specimen are correspondingly large, 

 and the surplus can be disposed of. 



In a wild state, it should also be borne in mind, the 

 degree of fertility is largely governed by certain inherited 

 instincts which determine at what period or periods, 

 and how often during the year, the breeding activities 

 shall be carried on. The theory under discussion is a 

 theory of the laws which govern the union of sperm cell 

 and ovum after copulation has taken place, and offers 

 no explanation of the conditions which determine how 

 or when it shall take place. Scientists are apt to expect 

 too much from a general principle. Thus Spencer attempts 

 to make his formula cover the whole field of animal and 

 vegetable fertility. He attempts to make it explain 

 those seasonal recurrences of the breeding instinct 

 which can only be explained by inherited, instinctive 

 associations. 



The varying periods of gestation among animals render 

 it necessary that copulation shall take place at different 

 periods of the year in order that the young may be born 

 at the most favourable season. These cases cannot be 

 all governed by a simple physiological reaction. They 

 must be governed by inherited instincts of the same 

 character as the nest-building instinct or the migratory 



