The Variation of Animals and Plants under Domestication, vol 2 | Page 4

HAVE BRED TRUE FROM
THEIR FIRST PRODUCTION--ON THE CROSSING OF DISTINCT
SPECIES IN RELATION TO THE FORMATION OF DOMESTIC
RACES.
CHAPTER 2.
XVI.--CAUSES WHICH INTERFERE WITH THE FREE CROSSING
OF VARIETIES-- INFLUENCE OF DOMESTICATION ON
FERTILITY.
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.
CHAPTER 2.
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 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.
CHAPTER 2.
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
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.
CHAPTER 2.
XIX.--SUMMARY OF THE FOUR LAST CHAPTERS, WITH

REMARKS ON HYBRIDISM.
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.
CHAPTER 2.
XX.--SELECTION BY MAN.
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.

CHAPTER 2.
XXI.--SELECTION, continued.
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.
CHAPTER 2.
XXII.--CAUSES OF VARIABILITY.
VARIABILITY DOES NOT NECESSARILY ACCOMPANY
REPRODUCTION--CAUSES ASSIGNED BY VARIOUS
AUTHORS--INDIVIDUAL DIFFERENCES--VARIABILITY OF
EVERY KIND DUE TO CHANGED CONDITIONS OF LIFE--ON
THE NATURE OF SUCH CHANGES--CLIMATE, FOOD, EXCESS
OF NUTRIMENT--SLIGHT CHANGES SUFFICIENT--EFFECTS
OF GRAFTING ON THE VARIABILITY OF

SEEDLING-TREES--DOMESTIC PRODUCTIONS BECOME
HABITUATED TO CHANGED CONDITIONS--ON THE
ACCUMULATIVE ACTION OF CHANGED
CONDITIONS--CLOSE INTERBREEDING AND THE
IMAGINATION OF THE MOTHER SUPPOSED TO CAUSE
VARIABILITY --CROSSING AS A CAUSE OF THE
APPEARANCE OF NEW CHARACTERS--VARIABILITY FROM
THE COMMINGLING OF CHARACTERS AND FROM
REVERSION--ON THE MANNER AND PERIOD OF ACTION OF
THE CAUSES WHICH EITHER DIRECTLY, OR INDIRECTLY
THROUGH THE REPRODUCTIVE SYSTEM, INDUCE
VARIABILITY.
CHAPTER 2.
XXIII.--DIRECT AND DEFINITE ACTION OF THE EXTERNAL
CONDITIONS OF LIFE.
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