: The Variation of Animals and Plants under Domestication — Volume 2 by Darwin Charles - Variation (Biology); Domestic animals; Plants Cultivated Botany; Animals-Domestic

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FREE INTERCROSSING OBLITERATES THE DIFFERENCES BETWEEN ALLIED BREEDS--WHEN THE NUMBERS OF TWO COMMINGLING BREEDS ARE UNEQUAL, ONE ABSORBS THE OTHER--THE RATE OF ABSORPTION DETERMINED BY PREPOTENCY OF TRANSMISSION, BY THE CONDITIONS OF LIFE, AND BY NATURAL SELECTION--ALL ORGANIC BEINGS OCCASIONALLY INTERCROSS; APPARENT EXCEPTIONS--ON CERTAIN CHARACTERS INCAPABLE OF FUSION; CHIEFLY OR EXCLUSIVELY THOSE WHICH HAVE SUDDENLY APPEARED IN THE INDIVIDUAL--ON THE MODIFICATION OF OLD RACES, AND THE FORMATION OF NEW RACES BY CROSSING--SOME CROSSED RACES HAVE BRED TRUE FROM THEIR FIRST PRODUCTION--ON THE CROSSING OF DISTINCT SPECIES IN RELATION TO THE FORMATION OF DOMESTIC RACES.

DIFFICULTIES IN JUDGING OF THE FERTILITY OF VARIETIES WHEN CROSSED--VARIOUS CAUSES WHICH KEEP VARIETIES DISTINCT, AS THE PERIOD OF BREEDING AND SEXUAL PREFERENCE--VARIETIES OF WHEAT SAID TO BE STERILE WHEN CROSSED--VARIETIES OF MAIZE, VERBASCUM, HOLLYHOCK, GOURDS, MELONS, AND TOBACCO, 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.

DEFINITION OF CLOSE INTERBREEDING--AUGMENTATION OF MORBID TENDENCIES--GENERAL EVIDENCE OF THE GOOD EFFECTS DERIVED FROM CROSSING, AND ON THE EVIL EFFECTS OF 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 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--CONCLUSION.

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 CONDITIONS OF LIFE--CONTABESCENCE OF THE ANTHERS-- MONSTROSITIES AS A CAUSE OF STERILITY--DOUBLE FLOWERS--SEEDLESS FRUIT-- STERILITY FROM THE EXCESSIVE DEVELOPMENT OF THE ORGANS OF VEGETATION--FROM LONG-CONTINUED PROPAGATION BY BUDS--INCIPIENT STERILITY THE PRIMARY CAUSE OF DOUBLE FLOWERS AND SEEDLESS FRUIT.

ON THE EFFECTS OF CROSSING--THE INFLUENCE OF DOMESTICATION ON FERTILITY--CLOSE INTERBREEDING--GOOD AND EVIL RESULTS FROM CHANGED CONDITIONS OF LIFE-- VARIETIES WHEN CROSSED NOT INVARIABLY FERTILE--ON THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND VARIETIES--CONCLUSIONS WITH RESPECT TO HYBRIDISM-- LIGHT THROWN ON HYBRIDISM BY THE ILLEGITIMATE PROGENY OF HETEROSTYLED PLANTS-- STERILITY OF CROSSED SPECIES DUE TO DIFFERENCES CONFINED TO THE REPRODUCTIVE SYSTEM--NOT ACCUMULATED THROUGH NATURAL SELECTION--REASONS WHY DOMESTIC VARIETIES ARE NOT MUTUALLY STERILE--TOO MUCH STRESS HAS BEEN LAID ON THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND CROSSED VARIETIES-- CONCLUSION.

SELECTION A DIFFICULT ART--METHODICAL, UNCONSCIOUS, AND NATURAL SELECTION-- RESULTS OF METHODICAL SELECTION--CARE TAKEN IN SELECTION--SELECTION WITH PLANTS--SELECTION CARRIED ON BY THE ANCIENTS AND BY SEMI-CIVILISED PEOPLE-- UNIMPORTANT CHARACTERS OFTEN ATTENDED TO--UNCONSCIOUS SELECTION--AS CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OUR DOMESTICATED ANIMALS CHANGED THROUGH THE ACTION OF UNCONSCIOUS SELECTION--INFLUENCE OF DIFFERENT BREEDERS ON THE SAME SUB-VARIETY--PLANTS AS AFFECTED BY UNCONSCIOUS SELECTION--EFFECTS OF SELECTION AS SHOWN BY THE GREAT AMOUNT OF DIFFERENCE IN THE PARTS MOST VALUED BY MAN.

NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS--CHARACTERS WHICH APPEAR OF TRIFLING VALUE OFTEN OF REAL IMPORTANCE--CIRCUMSTANCES FAVOURABLE TO SELECTION BY MAN--FACILITY IN PREVENTING CROSSES, AND THE NATURE OF THE CONDITIONS--CLOSE ATTENTION AND PERSEVERANCE INDISPENSABLE--THE PRODUCTION OF A LARGE NUMBER OF INDIVIDUALS ESPECIALLY FAVOURABLE--WHEN NO SELECTION IS APPLIED, DISTINCT RACES ARE NOT FORMED--HIGHLY-BRED ANIMALS LIABLE TO DEGENERATION--TENDENCY IN MAN TO CARRY THE SELECTION OF EACH CHARACTER TO AN EXTREME POINT, LEADING TO DIVERGENCE OF CHARACTER, RARELY TO CONVERGENCE-- CHARACTERS CONTINUING TO VARY IN THE SAME DIRECTION IN WHICH THEY HAVE ALREADY VARIED--DIVERGENCE OF CHARACTER, WITH THE EXTINCTION OF INTERMEDIATE VARIETIES, LEADS TO DISTINCTNESS IN OUR DOMESTIC RACES--LIMIT TO THE POWER OF SELECTION--LAPSE OF TIME IMPORTANT--MANNER IN WHICH DOMESTIC RACES HAVE ORIGINATED--SUMMARY.

SLIGHT MODIFICATIONS IN PLANTS FROM THE DEFINITE ACTION OF CHANGED CONDITIONS, IN SIZE, COLOUR, CHEMICAL PROPERTIES, AND IN THE STATE OF THE TISSUES--LOCAL DISEASES--CONSPICUOUS MODIFICATIONS FROM CHANGED CLIMATE OR FOOD, ETC.-- PLUMAGE OF BIRDS AFFECTED BY PECULIAR NUTRIMENT, AND BY THE INOCULATION OF POISON--LAND-SHELLS--MODIFICATIONS OF ORGANIC BEINGS IN A STATE OF NATURE THROUGH THE DEFINITE ACTION OF EXTERNAL CONDITIONS--COMPARISON OF AMERICAN AND EUROPEAN TREES--GALLS--EFFECTS OF PARASITIC FUNGI--CONSIDERATIONS OPPOSED TO THE BELIEF IN THE POTENT INFLUENCE OF CHANGED EXTERNAL CONDITIONS--PARALLEL SERIES OF VARIETIES--AMOUNT OF VARIATION DOES NOT CORRESPOND WITH THE DEGREE OF CHANGE IN THE CONDITIONS--BUD-VARIATION--MONSTROSITIES PRODUCED BY UNNATURAL TREATMENT--SUMMARY.

NISUS FORMATIVUS, OR THE CO-ORDINATING POWER OF THE ORGANISATION--ON THE EFFECTS OF THE INCREASED USE AND DISUSE OF ORGANS--CHANGED HABITS OF LIFE-- ACCLIMATISATION WITH ANIMALS AND PLANTS--VARIOUS METHODS BY WHICH THIS CAN BE EFFECTED--ARRESTS OF DEVELOPMENT--RUDIMENTARY ORGANS.

EXPLANATION OF TERM CORRELATION--CONNECTED WITH DEVELOPMENT--MODIFICATIONS CORRELATED WITH THE INCREASED OR DECREASED SIZE OF PARTS--CORRELATED VARIATION OF HOMOLOGOUS PARTS--FEATHERED FEET IN BIRDS ASSUMING THE STRUCTURE OF THE WINGS--CORRELATION BETWEEN THE HEAD AND THE EXTREMITIES--BETWEEN THE SKIN AND DERMAL APPENDAGES--BETWEEN THE ORGANS OF SIGHT AND HEARING--CORRELATED MODIFICATIONS IN THE ORGANS OF PLANTS--CORRELATED MONSTROSITIES--CORRELATION BETWEEN THE SKULL AND EARS--SKULL AND CREST OF FEATHERS--SKULL AND HORNS-- CORRELATION OF GROWTH COMPLICATED BY THE ACCUMULATED EFFECTS OF NATURAL SELECTION--COLOUR AS CORRELATED WITH CONSTITUTIONAL PECULIARITIES.

PRELIMINARY REMARKS. FIRST PART:--THE FACTS TO BE CONNECTED UNDER A SINGLE POINT OF VIEW, NAMELY, THE VARIOUS KINDS OF REPRODUCTION--REGROWTH OF AMPUTATED PARTS--GRAFT-HYBRIDS --THE DIRECT ACTION OF THE MALE ELEMENT ON THE FEMALE--DEVELOPMENT--THE FUNCTIONAL INDEPENDENCE OF THE UNITS OF THE BODY--VARIABILITY--INHERITANCE-- REVERSION. SECOND PART:--STATEMENT OF THE HYPOTHESIS--HOW FAR THE NECESSARY ASSUMPTIONS ARE IMPROBABLE--EXPLANATION BY AID OF THE HYPOTHESIS OF THE SEVERAL CLASSES OF FACTS SPECIFIED IN THE FIRST PART--CONCLUSION.

DOMESTICATION--NATURE AND CAUSES OF VARIABILITY--SELECTION--DIVERGENCE AND DISTINCTNESS OF CHARACTER--EXTINCTION OF RACES--CIRCUMSTANCES FAVOURABLE TO SELECTION BY MAN--ANTIQUITY OF CERTAIN RACES--THE QUESTION WHETHER EACH PARTICULAR VARIATION HAS BEEN SPECIALLY PREORDAINED.

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