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• Additions and Corrections to the Sixth Edition.
• An Historical Sketch of the Progress of Opinion On the Origin of Species.: Previously to the Publication of the First Edition of This Work.
• Origin of Species.
• Introduction.
• Chapter I.: Variation Under Domestication.
• 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.
• Chapter II.: Variation Under Nature.
• 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.
• Chapter III.: Struggle For Existence.
• 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.
• Chapter IV.: Natural Selection; Or the Survival of the Fittest.
• 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.
• Chapter V.: Laws of Variation.
• 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.
• Chapter VI.: Difficulties of the Theory.
• 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.
• Chapter VII.: Miscellaneous Objections to the Theory of Natural Selection.
• Chapter VIII.: Instinct.
• Inherited Changes of Habit Or Instinct In Domesticated Animals.
• Special Instincts.
• Objections to the Theory of Natural Selection As Applied to Instincts: Neuter and Sterile Insects.
• Summary.

Summary.

I have endeavoured in this chapter briefly to show that the mental qualities of our domestic animals vary, and that the variations are inherited. Still more briefly I have attempted to show that instincts vary slightly in a state of nature. No one will dispute that instincts are of the highest importance to each animal. Therefore there is no real difficulty, under changing conditions of life, in natural selection accumulating to any extent slight modifications of instinct which are in any way useful. In many cases habit or use and disuse have probably come into play. I do not pretend that the facts given in this chapter strengthen in any great degree my theory; but none of the cases of difficulty, to the best of my judgment, annihilate it. On the other hand, the fact that instincts are not always absolutely perfect and are liable to mistakes:—that no instinct can be shown to have been produced for the good of other animals, though animals take advantage of the instincts of others;—that the canon in natural history, of “Natura non facit saltum,” is applicable to instincts as well as to corporeal structure, and is plainly explicable on the foregoing views, but is otherwise inexplicable,—all tend to corroborate the theory of natural selection.

This theory is also strengthened by some few other facts in regard to instincts; as by that common case of closely allied, but distinct, species, when inhabiting distant parts of the world and living under considerably different conditions of life, yet often retaining nearly the same instincts. For instance, we can understand, on the principle of inheritance, how it is that the thrush of tropical South America lines its nest with mud, in the same peculiar manner as does our British thrush; how it is that the Hornbills of Africa and India have the same extraordinary instinct of plastering up and imprisoning the females in a hole in a tree, with only a small hole left in the plaster through which the males feed them and their young when hatched; how it is that the male wrens (Troglodytes) of North America build “cock-nests,” to roost in, like the males of our Kitty-wrens,—a habit wholly unlike that of any other known bird. Finally, it may not be a logical deduction, but to my imagination it is far more satisfactory to look at such instincts as the young cuckoo ejecting its foster-brothers,—ants making slaves,—the larvæ of ichneumonidæ feeding within the live bodies of caterpillars,—not as specially endowed or created instincts, but as small consequences of one general law leading to the advancement of all organic beings,—namely, multiply vary, let the strongest live and the weakest die.

end of volume i.