92 GOOD FROM CROSSING. Chap. XVII. 



CHAPTER XVII. 



ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL EFFECTS 

 OF CLOSE INTERBREEDING. 



DEFINITION OF CLOSE INTERBREEDING AUGMENTATION OP MORBID TEN- 

 DENCIES — GENERAL EVIDENCE OP THE GOOD EFFECTS DERIVED FROM 



CROSSING, AND ON THE EVIL EFFECTS FROM CLOSE INTERBREEDING 



CATTLE, CLOSELY INTERBRED; HALF-WILD CATTLE LONG KEPT IN THE 

 SAME PARKS — SHEEP — FALLOW-DEER — DOGS, RABBITS, PIGS — MAN, ORIGIN 

 OF HIS ABHORRENCE OF INCESTUOUS MARRIAGES — FOWLS — PIGEONS — HIVE- 

 BEES — PLANTS, GENERAL CONSIDERATIONS ON THE BENEFITS DERIVED FROM 

 CROSSINCi MELONS, FRUIT-TREES, PEAS, CABBAGES, WHEAT, AND FOREST- 

 TREES — ON THE INCREASED SIZE OF HYBRID PLANTS, NOT EXCLUSIVELY 

 DUE TO THEIR STERILITY — ON CERTAIN PLANTS WHICH EITHER NOR- 

 MALLY OR ABNORMALLY ARE SELF-IMPOTENT, BUT ARE FERTILE, BOTH 

 ON THE MALE AND FEMALE SIDE, WHEN CROSSED WITH DISTINCT INDI- 

 VIDUALS EITHER OF THE SAME OR ANOTHER SPECIES — CONCLUSION. 



The gain in constitutional vigour, derived from an occasional 

 cross between individuals of the same variety, but belonging 

 to distinct families, or between distinct varieties, has not 

 been' so largely or so frequently discussed, as have the evil 

 effects of too close interbreeding. But the former point is 

 the more important of the two, inasmuch as the evidence is 

 more "decisive. The evil results from close interbreeding are 

 difficult to detect, for they accumulate slowly, and differ 

 much in degree with different species ; whilst the good effects 

 which almost invariably follow a cross are from the first 

 manifest. It should, however, be clearly understood that the 

 advantage of close interbreeding, as far as the retention of 

 character is concerned, is indisputable, and often outweighs 

 the evil of a slight loss of constitutional vigour. In relation 

 to the subject of domestication, the whole question is of some 

 importance, as too close interbreeding interferes with the 

 improvement of old races. It is important as indirectly 

 bearing on Hybridism ; and possibly on the extinction of 

 species, when any form has become so rare that only a few 

 individuals remain within a confined area. It bears in an 



