NATURAL SELECTION 103 



slight to very strong, it may well be that where the 

 inheritance is weak the influence of generic pressure 

 will overcome the overlying individual variations, pre- 

 venting them from appearing, and replacing them by 

 the generic markings. The difference between the 

 various breeds of pigeons is very extraordinary ; never- 

 theless, under the influence of the generic pressure 

 which is their common inheritance, we find individuals 

 of all the breeds throwing off their varietal characters, 

 and appearing as if they were the direct offspring of 

 parental stock-doves. Individuals belonging to different 

 breeds, such as the tumbler, the carrier, the runt, the 

 barb, the pouter, the turbit, the jacobin, the trumpeter, 

 the laugher, and the fantail, come into the world 

 devoid of their proper characters as such, and differing 

 in no respect from the wild wood-pigeon, their common 

 ancestor. 



The difference between generic characters and indi- 

 vidual variations is here made very apparent. The 

 former persist in appearing sporadically, long after 

 their pristine vigour has waned during a long series 

 of generations, owing to breeds derived from a common 

 specific form, or species derived from genera perhaps 

 long extinct, inheriting in all their individuals, from 

 their unbroken descent, the tendency to reproduce 

 them. Individual variations, on the other hand, of 

 all frail things the frailest, the most fugitive and 

 evanescent, are unable to maintain themselves in the 

 free intercrossing that takes place in Nature, and die 

 out in the course of a few generations. The same 



