MANIFESTED IN THE ANIMAL KINGDOM ?a 



instinct, and these instincts will be awakened by certain 

 seasonal associations. 



" At any rate it is not correct to say with Dr. Gruenhagen, 

 that * the general wedding feast is spring, when awaken- 

 ing nature opens to most animals new and ample sources 

 of living. 5 This is certainly true of reptiles and birds, 

 but not of mammals ; every month or season of the year 

 is the pairing season of one or another mammalian species ; 

 but notwithstanding this apparent irregularity, the pairing 

 time of each species is bound by an unfailing law ; it 

 sets in earlier or later, according as the period of gestation 

 lasts longer or shorter, so that the young may be born at 

 the time when they are most likely to survive. . . . Far 

 from depending on any general physiological law, the 

 rut is then adapted to the requirements of each species 

 separately." J 



Under domestication, where warmth, shelter, and food 

 can be obtained in abundance all the year round, these 

 instincts tend to fall into abeyance, and domesticated 

 varieties lend themselves readily to manipulation by man. 

 Manipulation is, indeed, an important cause of the in- 

 creased fertility of domesticated varieties. Thus when fowls 

 become broody various ingenious devices are resorted to 

 in order to get rid of the brooding instinct, such as putting 

 the bird under a bucket. In some varieties of fowls the 

 brooding instinct has been almost eliminated by selection. 



We may now examine the evidence bearing upon the 

 principle provided by domesticated animals. Darwin will 

 again be the principal source of information. Speaking 

 of race-horses he says : " During eleven years a record 

 was kept of the number of mares which proved barren 

 or prematurely slipped their foals ; and it deserves 

 notice as showing how infertile these highly nurtured 

 1 The History of Human Marriage, Westennarck. 



