On the
Origin of Species
1859
by
Charles Darwin
'But
with regard to the material world, we can at least go so far as this--we can
perceive that events are brought about not by insulated interpositions of
Divine power, exerted in each particular case, but by the establishment of
general laws.' W. Whewell: Bridgewater Treatise.
'To
conclude, therefore, let no man out of a weak conceit of sobriety, or an
ill-applied moderation, think or maintain, that a man can search too far or be
too well studied in the book of God's word, or in the book of God's works;
divinity or philosophy; but rather let men endeavour an endless progress or
proficience in both.' Bacon: Advancement of Learning.
Down,
Bromley, Kent, October 1st, 1859.
Chapter I: 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 II: 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 III: 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.
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.
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 VI: Difficulties of 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.
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.
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 IX: 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
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 X: 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 XI: 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 XII: 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 XIII: Mutual Affinities of Organic Beings
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
explained--Summary.
Chapter XIV: Recapitulation and Conclusions
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.
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