On the Origin of Species By Means of Natural Selection / Or, the Preservation of Favoured Races in the Struggle for Life

by Charles Darwin

[CHAPTER 3. 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 4. 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 descendants from a common parent.
Explains the Grouping of all organic beings.

[CHAPTER 5. 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 6. 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 7. 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 8. HYBRIDISM.]
Distinction between the sterility of first crosses and of hybrids.
Sterility various in degree, not universal, affected by close interbreeding, 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 9. 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 vast lapse of time, as inferred from the rate of deposition and of denudation.
On the poorness of our palæontological 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 10. 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 11. 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 12. 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.