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Table of Contents PREFACE 001 INTRODUCTION 015 CHAPTER I VARIATION UNDER DOMESTICATION 021 CAUSES OF VARIABILITY 022 EFFECTS OF HABIT AND OF THE USE OR DISUSE OF PARTS; CORRELATED VARIATION; INHERITANCE 027 CHARACTER OF DOMESTIC VARIETIES; DIFFICULTY OF DISTINGUISHING BETWEEN VARIETIES AND SPECIES; ORIGIN OF DOMESTIC VARIETIES FROM ONE OR MORE SPECIES 032 BREEDS OF THE DOMESTIC PIGEON, THEIR DIFFERENCES AND ORIGIN 037 PRINCIPLES OF SELECTION ANCIENTLY FOLLOWED, AND THEIR EFFECTS 046 UNCONSCIOUS SELECTION 051 I CIRCUMSTANCES FAVOURABLE TO MAN'S POWER OF SELECTION 058 CHAPTER II VARIATION UNDER NATURE 063 INDIVIDUAL DIFFERENCES 065 DOUBTFUL SPECIES 068 WIDE-RANGING, MUCH DIFFUSED, AND COMMON SPECIES VARY MOST 077 SPECIES OF THE LARGER GENERA IN EACH COUNTRY VARY MORE FREQUENTLY THAN THE SPECIES OF THE SMALLER GENERA 079 MANY OF THE SPECIES INCLUDED WITHIN THE LARGER GENERA RESEMBLE VARIETIES IN BEING VERY CLOSELY, BUT UNEQUALLY, RELATED TO EACH OTHER, AND IN HAVING RESTRICTED RANGES 082 SUMMARY 084 CHAPTER III STRUGGLE FOR EXISTENCE 087 THE TERM, STRUGGLE FOR EXISTENCE, USED IN A LARGE SENSE 090 GEOMETRICAL RATIO OF INCREASE 091 NATURE OF THE CHECKS TO INCREASE 095 II COMPLEX RELATIONS OF ALL ANIMALS AND PLANTS TO EACH OTHER IN THE STRUGGLE FOR EXISTENCE 099 STRUGGLE FOR LIFE MOST SEVERE BETWEEN INDIVIDUALS AND VARIETIES OF THE SAME SPECIES 104 CHAPTER IV NATURAL SELECTION; OR THE SURVIVAL OF THE FITTEST 109 SEXUAL SELECTION 119 ILLUSTRATIONS OF THE ACTION OF NATURAL SELECTION, OR THE SURVIVAL OF THE FITTEST 122 ON THE INTERCROSSING OF INDIVIDUALS 131 CIRCUMSTANCES FAVOURABLE FOR THE PRODUCTION OF NEW FORMS THROUGH NATURAL SELECTION 137 EXTINCTION CAUSED BY NATURAL SELECTION 145 DIVERGENCE OF CHARACTER 147 THE PROBABLE EFFECTS OF THE ACTION OF NATURAL SELECTION THROUGH DIVERGENCE OF CHARACTER AND EXTINCTION, ON THE DESCENDANTS OF A COMMON ANCESTOR 152 ON THE DEGREE TO WHICH ORGANISATION TENDS TO ADVANCE 163 CONVERGENCE OF CHARACTER 168 SUMMARY OF CHAPTER 171 III CHAPTER V LAWS OF VARIATION 175 EFFECTS OF THE INCREASED USE AND DISUSE OF PARTS, AS CONTROLLED BY NATURAL SELECTION 178 ACCLIMATISATION 184 CORRELATED VARIATION 188 COMPENSATION AND ECONOMY OF GROWTH 192 MULTIPLE, RUDIMENTARY, AND LOWLY-ORGANISED STRUCTURES ARE VARIABLE 194 A PART DEVELOPED IN ANY SPECIES IN AN EXTRAORDINARY DEGREE OR MANNER, IN COMPARISON WITH THE SAME PART IN ALLIED SPECIES, TENDS TO BE HIGHLY VARIABLE 195 SPECIFIC CHARACTERS MORE VARIABLE THAN GENERIC CHARACTERS 199 SECONDARY SEXUAL CHARACTERS VARIABLE 201 DISTINCT SPECIES PRESENT ANALOGOUS VARIATIONS, SO THAT A VARIETY OF ONE SPECIES OFTEN ASSUMES A CHARACTER PROPER TO AN ALLIED SPECIES, OR REVERTS TO SOME OF THE CHARACTERS OF AN EARLY PROGENITOR 204 SUMMARY 213 IV CHAPTER VI DIFFICULTIES OF THE THEORY 217 ON THE ABSENCE OR RARITY OF TRANSITIONAL VARIETIES 219 ON THE ORIGIN AND TRANSITION OF ORGANIC BEINGS WITH PECULIAR HABITS AND STRUCTURE 226 ORGANS OF EXTREME PERFECTION AND COMPLICATION 233 MODES Of TRANSITION 238 SPECIAL DIFFICULTIES OF THE THEORY OF NATURAL SELECTION 243 ORGANS OF LITTLE APPARENT IMPORTANCE, AS AFFECTED BY NATURAL SELECTION 253