CONTENTS. V 



RENDERED 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 CUOSSING, AND ON THE EVIL 

 EFFECTS OF CLOSE INTERBEEEDING. 



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; 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 SIZE 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 



CHAPTER 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 



