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On the Origin of Species by Means of Natural Selection,
Preservation of Favoured Races in the Struggle for Life.
By Charles Darwin
Chapter I(A,B, C)
Variation under Domestication
Causes of Variability -- Effects of Habit -- Correlation of Growth --Inheritance -- Character of Domestic Varieties -- Difficulty ofdistinguishing between Varieties and Species -- Origin of DomesticVarieties from one or more Species -- Domestic Pigeons, their Differencesand Origin -- Principle of Selection anciently followed, its Effects --Methodical and Unconscious Selection -- Unknown Origin of our DomesticProductions -- Circumstances favourable to Man's power of Selection.
Variation under Nature
Variability -- Individual Differences -- Doubtful species -- Wide ranging,much diffused, and common species vary most -- Species of the larger generain any country vary more than the species of the smaller genera -- Many ofthe species of the larger genera resemble varieties in being very closely,but unequally, related to each other, and in having restricted ranges.
Struggle for Existence
Bears on natural selection -- The term used in a wide sense -- Geometricalpowers of increase -- Rapid increase of naturalised animals and plants --Nature of the checks to increase -- Competition universal -- Effects ofclimate -- Protection from the number of individuals -- Complex relationsof all animals and plants throughout nature -- Struggle for life mostsevere between individuals and varieties of the same species; often severebetween species of the same genus -- The relation of organism to organismthe most important of all relations.
Chapter IV(A,B, C)
Natural Selection -- its power compared with man's selection -- its poweron characters of trifling importance -- its power at all ages and on bothsexes -- Sexual Selection -- On the generality of intercrosses betweenindividuals of the same species -- Circumstances favourable andunfavourable to Natural Selection, namely, intercrossing, isolation, numberof individuals -- Slow action -- Extinction caused by Natural Selection --Divergence of Character, related to the diversity of inhabitants of anysmall area, and to naturalisation -- Action of Natural Selection, throughDivergence of Character and Extinction, on the descendants from a commonparent -- Explains the Grouping of all organic beings.
Chapter V(A,B, C)
Laws of Variation
Effects of external conditions -- Use and disuse, combined with naturalselection; organs of flight and of vision -- Acclimatisation -- Correlationof growth -- Compensation and economy of growth -- False correlations --Multiple, rudimentary, and lowly organised structures variable -- Partsdeveloped in an unusual manner are highly variable: specific charactersmore variable than generic: secondary sexual characters variable --Species of the same genus vary in an analogous manner -- Reversions tolong-lost characters -- Summary.
Chapter VI(A,B, C)
Difficulties on Theory
Difficulties on the theory of descent with modification -- Transitions --Absence or rarity of transitional varieties -- Transitions in habits oflife -- Diversified habits in the same species -- Species with habitswidely 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 thetheory of Natural Selection.
Chapter VII(A,B, C)
Instincts comparable with habits, but different in their origin --Instincts graduated -- Aphides and ants -- Instincts variable -- Domesticinstincts, their origin -- Natural instincts of the cuckoo, ostrich, andparasitic 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.
Distinction between the sterility of first crosses and of hybrids --Sterility various in degree, not universal, affected by closeinterbreeding, removed by domestication -- Laws governing the sterility ofhybrids -- Sterility not a special endowment, but incidental on otherdifferences -- 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 notuniversal -- Hybrids and mongrels compared independently of their fertility-- Summary.
On the Imperfection of the Geological Record
On the absence of intermediate varieties at the present day -- On thenature of extinct intermediate varieties; on their number -- On the vastlapse of time, as inferred from the rate of deposition and of denudation --On the poorness of our palaeontological collections -- On the intermittenceof geological formations -- On the absence of intermediate varieties in anyone formation -- On the sudden appearance of groups of species -- On theirsudden appearance in the lowest known fossiliferous strata.
Chapter X(A,B, C)
On the Geological Succession of Organic Beings
On the slow and successive appearance of new species -- On their differentrates of change -- Species once lost do not reappear -- Groups of speciesfollow the same general rules in their appearance and disappearance as dosingle species -- On Extinction -- On simultaneous changes in the forms oflife throughout the world -- On the affinities of extinct species to eachother and to living species -- On the state of development of ancient forms-- On the succession of the same types within the same areas -- Summary ofpreceding and present chapters.
Chapter XI(A,B, C)
Present distribution cannot be accounted for by differences in physicalconditions -- Importance of barriers -- Affinity of the productions of thesame continent -- Centres of creation -- Means of dispersal, by changes ofclimate and of the level of the land, and by occasional means -- Dispersalduring the Glacial period co-extensive with the world.
Geographical Distribution -- continued
Distribution of fresh-water productions -- On the inhabitants of oceanicislands -- Absence of Batrachians and of terrestrial Mammals -- On therelation 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 XIII(A,B, C)
Mutual Affinities of Organic Beings:
Morphology: Embryology: Rudimentary Organs
Classification, groups subordinate to groups -- Natural system -- Rules anddifficulties in classification, explained on the theory of descent withmodification -- Classification of varieties -- Descent always used inclassification -- 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 sameindividual -- Embryology, laws of, explained by variations not superveningat an early age, and being inherited at a corresponding age -- RudimentaryOrgans; their origin explained -- Summary.
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 thetheory of natural selection may be extended -- Effects of its adoption onthe study of Natural history -- Concluding remarks.