CONTENTS. V 



KENDERED IN SOME DEGREE MUTUALLY STERILE— DOMESTICATION 

 ELIMINATES THE TENDENCY TO STERILITY NATURAL TO SPECIES 

 WHEN CROSSED — ON THE INCREASED FERTILITY OF UNCROSSED 

 ANIMALS AND PLANTS FROM DOMESTICATION AND CULTIVATION. 



Pages 78-91 



CHAPTER XVII. 



ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL 

 EFFECTS OF CLOSE INTERBREEDING. 



DEFINITION OF CLOSE INTERBREEDING — AUGMENTATION OF MORBID 



TENDENCIES GENERAL EVIDENCE OF THE GOOD EFFECTS DERIVED 



FROM CROSSING, AND ON THE EVIL EFFECTS OF CLOSE INTERBREED- 

 ING — CATTLE, CLOSELY INTERBRED J 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 CONSIDERA- 

 TIONS ON THE BENEFITS DERIVED FROM CROSSING — MELONS, FRUIT- 

 TREES, PEAS, CABBAGES, WHEAT, AND FOREST- TREES — ON THE 

 INCREASED SLZE OF HYBRID PLANTS, NOT EXCLUSIVELY DUE TO 

 THEIR STERILITY — ON CERTAIN PLANTS WHICH EITHER NORMALLY 

 OR ABNORMALLY ARE SELF-IMPOTENT, BUT ARE FERTILE BOTH 

 ON THE MALE AND FEMALE SIDE, WHEN CROSSED WITH DISTINCT 

 INDIVIDUALS EITHER OF THE SAME OR ANOTHER SPECIES — CON- 

 CLUSION 92-126 



CHAPTEE XVIII. 



ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED 

 CONDITIONS OF LIFE : STERILITY FROM VARIOUS CAUSES. 



ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF 

 LIFE— STERILITY FROM CHANGED CONDITIONS, IN ANIMALS, IN 

 THEIR NATIVE COUNTRY AND IN MENAGERIES — MAMMALS, BIRDS, 



AND INSECTS LOSS OF SECONDARY SEXUAL CHARACTERS AND OF 



INSTINCTS — CAUSES OF STERILITY — STERILITY OF DOMESTICATED 

 ANIMALS FROM CHANGED CONDITIONS — SEXUAL INCOMPATIBILITY 

 OF INDIVIDUAL ANIMALS — STERILITY OF PLANTS FROM CHANGED 



