82 THE LAW OF BIRTHS AND DEATHS 



to individuation and the amount devoted to reproduction 

 increase together. 



" With all highly bred animals there is more or less 

 difficulty in getting them to procreate quickly, and all 

 suffer much from delicacy of constitution, A great 

 judge of rabbits says : * The long-eared does are often 

 too highly bred or forced in their growth to be of much 

 value as breeders, often turning out barren or bad 

 mothers.' " l 



Highly bred animals are, generally speaking, those 

 which have been bred for qualities intimately associated 

 with or the result of a high development of nervous 

 energy. Vigour and grace of carriage, brightness of 

 colouring, and most of the qualities valued by fanciers, 

 are intimately connected with the vitality of the nervous 

 system. A highly bred animal or bird is usually a " bundle 

 of nerves." 



Cats and dogs provide no special information beyond 

 the general facts that with highly bred animals conception 

 is likely to be uncertain and the litters very irregular in 

 size, and that high-feeding and lack of exercise are likely 

 to result in sterility. Together with several other 

 domesticated species they are not manipulated in such 

 a way as to throw any special light on the problem of 

 fertility. 



The domestic fowl, however, shows us the operation 

 of the principle admirably. " Birds offer still better 

 evidence of increased fertility from domestication ; the 

 hen of the wild Gallas bankiva lays from six to ten eggs, 

 a number which would be thought nothing of with the 

 domestic hen." a It is a notorious fact that domestic 

 fowls owe their present high degree of fertility to long 



1 Variation oj Animals and Plants under Domestication, chap. xvii. 

 Ibid., chap, xvi. 



