Causes of Variability

Effects of Habit and of the Use or Disuse of Parts; Correlated Variation; Inheritance

Character of Domestic Varieties; Difficulty of Distinguishing Between Varieties and Species; Origin of Domestic Varieties from One or More Species

Breeds of the Domestic Pigeon, Their Differences and Origin

Principles of Selection Anciently Followed, and Their Effects

Unconscious Selection

Circumstances Favourable to Man’s Power of Selection

Individual Differences

Doubtful Species

Wide-Ranging, Much Diffused, and Common Species Vary Most

Species of the Larger Genera in Each Country Vary More Frequently Than the Species of the Smaller Genera

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

Summary

The Term, Struggle for Existence, Used in a Large Sense

Geometrical Ratio of Increase

Nature of the Checks to Increase

Complex Relations of All Animals and Plants to Each Other in the Struggle for Existence

Struggle for Life Most Severe Between Individuals and Varieties of the Same Species

Sexual Selection

Illustrations of the Action of Natural Selection, or the Survival of the Fittest

On the Intercrossing of Individuals

Circumstances Favourable for the Production of New Forms Through Natural Selection

Extinction Caused by Natural Selection

Divergence of Character

The Probable Effects of the Action of Natural Selection Through Divergence of Character and Extinction, on the Descendants of a Common Ancestor

On the Degree to Which Organisation Tends to Advance

Convergence of Character

Summary of Chapter

Effects of the Increased Use and Disuse of Parts, as Controlled by Natural Selection

Acclimatisation

Correlated Variation

Compensation and Economy of Growth

Multiple, Rudimentary, and Lowly-Organised Structures Are Variable

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

Specific Characters More Variable Than Generic Characters

Secondary Sexual Characters Variable

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

Summary

On the Absence or Rarity of Transitional Varieties

On the Origin and Transition of Organic Beings with Peculiar Habits and Structure

Organs of Extreme Perfection and Complication

Modes of Transition

Special Difficulties of the Theory of Natural Selection

Organs of Little Apparent Importance, as Affected by Natural Selection

Utilitarian Doctrine, How Far True: Beauty, How Acquired

Summary: The Law of Unity of Type and of the Conditions of Existence Embraced by the Theory of Natural Selection

Inherited Changes of Habit or Instinct in Domesticated Animals

Special Instincts

Instincts of the Cuckoo

Slave-Making Instinct

Cell-Making Instinct of the Hive-Bee

Objections to the Theory of Natural Selection as Applied to Instincts: Neuter and Sterile Insects

Summary

Degrees of Sterility

Laws Governing the Sterility of First Crosses and of Hybrids

Origin and Causes of the Sterility of First Crosses and of Hybrids

Reciprocal Dimorphism and Trimorphism

Fertility of Varieties When Crossed, and of Their Mongrel Offspring, Not Universal

Hybrids and Mongrels Compared, Independently of Their Fertility

Summary of Chapter

On the Lapse of Time, as Inferred from the Rate of Deposition and Extent of Denudation

On the Poorness of Palaeontological Collections

On the Absence of Numerous Intermediate Varieties in Any Single Formation

On the Sudden Appearance of Whole Groups of Allied Species

On the Sudden Appearance of Groups of Allied Species in the Lowest Known Fossiliferous Strata

On Extinction

On the Forms of Life Changing Almost Simultaneously Throughout the World

On the Affinities of Extinct Species to Each Other, and to Living Forms

On the State of Development of Ancient Compared with Living Forms

On the Succession of the Same Types Within the Same Areas, During the Later Tertiary Periods

Summary of the Preceding and Present Chapters

Single Centres of Supposed Creation

Means of Dispersal

Dispersal During the Glacial Period

Alternate Glacial Periods in the North and South

Freshwater Productions

On the Inhabitants of Oceanic Islands

Absence of Batrachians and Terrestrial Mammals on Oceanic Islands

On the Relations of the Inhabitants of Islands to Those of the Nearest Mainland

Summary of the Last and Present Chapters

Analogical Resemblances

On the Nature of the Affinities Connecting Organic Beings

Morphology

Development and Embryology

Rudimentary, Atrophied, and Aborted Organs

Summary