Chap. XVI. INCREASED FERTILITY FROM DOMESTICATION. 89 



that our domesticated pigs belong to at least two specific 

 types, S. scrofa and indicus. Kow a widely extended analogy 

 leads to the belief that if these several allied species, when 

 first reclaimed, had been crossed, they would have exhibited, 

 both in their first unions and in their hybrid offspring, some 

 degree of sterility. Nevertheless, the several domesticated 

 races descended from them are now all, as far as can be 

 ascertained, perfectly fertile together. If this reasoning be 

 trustworthy, and it is apparently sound, we must admit the 

 Pal las i an doctrine that long-continued domestication tends 

 to eliminate that sterility which is natural to species when 

 crossed in their aboriginal state. 



Ofi increased Fertility from Domestication and Cultivation. 



Increased fertility from domestication, without any refer- 

 ence to crossing, may be here briefly considered. This subject 

 bears indirectly on two or three points connected with the 

 modification of organic beings. As Buffon long ago re- 

 marked,^^ domestic animals breed oftener in the year and 

 produce more young at a birth than wild animals of the same 

 species ; they, also, sometimes breed at an earlier age. The 

 case would hardly have deserved further notice, had not 

 some authors lately attempted to show that fertility increases 

 and decreases in an inverse ratio with the amount of food. 

 This strange doctrine has apparently arisen from individual 

 animals when supplied with an inordinate quantity of food, 

 and from plants of many kinds when grown on excessively 

 rich soil, as on a dunghill, becoming sterile : but to this 

 latter point I shall have occasion presently to return. With 

 hardly an exception, our domesticated animals, which have 

 been long habituated to a regular and copious supply of food, 

 witliout the labour of searching for it, are more fertile than 

 the corresponding wild animals. It is notorious how fre- 

 quently cats and dogs breed, and how many young they 

 produce at a birth. The wild rabbit is said generally to 



^^ Quoted by Isid. Geoffroy St. the present subject has appeared in 



Hilaire, ' Hist. Naturelle Generale,' Mr. Herbert Spencer's ' Principles of 



torn. iii. p. 476. Since this MS. has Biology,' vol. ii., 1867, p. 457 ct seq. 

 been sent to press a full discussion on 



