REVERSION. 47 



chance of coming into action, and the only other 

 mode of putting an end to an unfit family extinction 

 is called upon. Thus the intermarriage of dwarfs 

 or giants is seldom fruitful, while the children of 

 parents both of whom suffer from scrofula, insanity, 

 epilepsy, &c., of a well-marked type are generally 

 carried off in infancy, die before the procreative period 

 is reached, or are sterile. But the result is very 

 different if the diseased or otherwise abnormal one 

 marry a person belonging to some other variety than 

 his own, as the phthisical the robust, or the giant or 

 dwarf one of ordinary stature. Here the law of re- 

 version comes into play, and in the offspring of such 

 unions there is a great effort made to " throw back " 

 to the original stock, that is, in the examples we have 

 taken, the fairly healthy and the mediocre in stature 

 respectively. 



Hence we have the rule, that the offspring of indi- 

 viduals of different varieties tends strongly to throw 

 back to the normal, while the offspring of parents 

 belonging to the same variety tends to retain the 

 peculiar characters of that variety, and when the 

 characters become extreme the stock dies out. This 

 rule is well known to breeders of animals, who will 

 tell you that breeding " in and in," that is, breeding 

 from animals belonging to the same variety, will per- 

 petuate, and in time accentuate the peculiar qualities 

 of the variety, be they good or bad, while " crossing," 

 which means breeding from animals belonging to 

 different varieties, will reduce the characters peculiar 



