Editor's Introduction
Note on This Edition
An Historical Sketch
Introduction

Chapter One: Variation Under Domestication
Causes of Variability - Effects of Habit - Correlation of Growth - Inheritance - Character of Domestic Varieties - Difficulty of distinguishing between Varieties and Species - Origin of Domestic Varieties from one or more Species - Domestic Pigeons, their Differences and Origin - Principle of Selection anciently followed, its Effects - Methodical and Unconscious Selection - Unknown Origin of our Domestic Productions - Circumstances favourable to Man's power of Selection

Chapter Two: Variation Under Nature
Variability - Individual differences - Doubtful species - Wide ranging, much diffused, and common species vary most - Species of the larger genera in any country vary more than the species of the smaller genera - Many of the species of the larger genera resemble varieties in being very closely, but unequally, related to each other, and in having restricted ranges

Chapter Three: Struggle for Existence
Bears on natural selection - The term used in a wide sense - Geometrical powers of increase - Rapid increase of naturalised animals and plants - Nature of the checks to increase - Competition universal - Effects of climate - Protection from the number of individuals - Complex relations of all animals and plants throughout nature - Struggle for life most severe between individuals and varieties of the same species; often severe between species of the same genus - The relation of organism to organism the most important of all relations

Chapter Four: Natural Selection
Natural Selection - its power compared with man's selection - its power on characters of trifling importance - its power at all ages and on both sexes - Sexual Selection - On the generality of intercrosses between individuals of the same species - Circumstances favourable and unfavourable to Natural Selection, namely, intercrossing, isolation, number of individuals - Slow action - Extinction caused by Natural Selection - Divergence of Character, related to the diversity of inhabitants of any small area, and to naturalisation - Action of Natural Selection, through Divergence of Character and Extinction, on the descendents from a common parent - Explains the Grouping of all organic beings

Chapter Five: Laws of Variation
Effects of external conditions - Use and disuse, combined with natural selection; organs of flight and of vision - Acclimatisation - Correlation of growth - Compensation and economy of growth - False correlations - Multiple, rudimentary, and lowly organised structures variable - Parts developed in an unusual manner are highly variable: specific characters more variable than generic: secondary sexual characters variable - Species of the same genus vary in an analogous manner - Reversions to long-lost characters - Summary

Chapter Six: Difficulties on Theory
Difficulties on the theory of descent with modification - Transitions - Absence or rarity of transitional varieties - Transitions in habits of life - Diversified habits in the same species - Species with habits widely different from those of their allies - Organs of extreme perfection - Means of transition - Cases of difficulty - Natura non facit saltum - Organs of small importance - Organs not in all cases absolutely perfect - The law of Unity of Type and of the Conditions of Existence embraced by the theory of Natural Selection

Chapter Seven: Instinct
Instincts comparable with habits, but different in their origin - Instincts graduated - Aphides and ants - Instincts variable - Domestic instincts, their origin - Natural instincts of the cuckoo, ostrich, and parasitic bees - Slave-making ants - Hive-bee, its cell-making instinct - Difficulties on the theory of the Natural Selection of instincts - Neuter or sterile insects - Summary

Chapter Eight: Hybridism
Distinction between sterility of first crosses and of hybrids - Sterility various in degree, not universal, affected by close inter-breeding, removed by domestication - Laws governing the sterility of hybrids - Sterility not a special endowment, but incidental on other differences - Causes of the sterility of first crosses and of hybrids - Parallelism between the effects of changed conditions of life and crossing - Fertility of varieties when crossed and of their mongrel offspring not universal - Hybrids and mongrels compared independently of their fertility - Summary

Chapter Nine: On the Imperfection of the Geological Record
On the absence of intermediate varieties at the present day - On the nature of extinct intermediate varieties; on their number - On the last vast lapse of time, as inferred from the rate of deposition and of denudation - On the poorness of our palaeontological collections - On the intermittence of geological formations - On the absence of intermediate varieties in any one formation - On the sudden appearance of groups of species - On their sudden appearance in the lowest known fossiliferous strata

Chapter Ten: On the Geological Succession of Organic Beings
On the slow and successive appearance of new species - On their different rates of change - Species once lost do not reappear - Groups of species follow the same general rules in their appearance and disappearance as do single species - On Extinction - On simultaneous changes in the forms of life throughout the world - On the affinities of extinct species to each other and to living species - On the state of development of ancient forms - On the succession of the same types within the same areas - Summary of preceding and present chapters

Chapter Eleven: Geographical Distribution
Present distribution cannot be accounted for by differences in physical conditions - Importance of barriers - Affinity of the productions of the same continent - Centres of creation - Means of dispersal, by changes of climate and of the level of the land, and by occasional means - Dispersal during the Glacial period co-extensive with the world

Chapter Twelve: Geographical Distribution continued
Distribution of fresh-water productions - On the inhabitants of oceanic islands - Absence of Batrachians and of terrestrial Mammals - On the relation of the inhabitants of islands to those of the nearest mainland - On colonisation from the nearest source with subsequent modification - Summary of the last and present chapters

Chapter Thirteen: Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Organs
Classification, groups subordinate to groups - Natural system - Rules and difficulties in classification, explained on the theory of descent with modification - Classification of varieties - Descent always used in classification - Analogical or adaptive characters - Affinities, general, complex and radiating - Extinction separates and defines groups - Morphology, between members of the same class, between parts of the same individual - Embryology, laws of, explained by variations not supervening at an early age, and being inherited at a corresponding age - Rudimentary organs, their origin explain - Summary

Chapter Fourteen: Recapitulation and Conclusion
Recapitulation of the difficulties on the theory of Natural Selection - Recapitulation of the general and special circumstances in its favour - Causes of the general belief in the immutability of species - How far the theory of natural selection may be extended - Effects of its adoption on the study of Natural history - Concluding remarks

Bibliography
Glossary