THE ORIGIN OF SPECIES- CHARLES DARWIN

(01)

THE O R I G I N OF SPECIES

BY MEANS OF NATURAL SELECTION,

BY
CHARLES DARWIN, M A ,
FELLOW OF T H E R O Y A L
AUTHOR OF 'JOURNAL OF RESEARCHES DURING XI. M.
ROUND THE WORLD.'





. .
C H A P T E R 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 2nd Unconscious Selection -Unknown
Origin of our Domestic Productions -Circumstances favourable
to Man’s powerof Selection . . . . . . . . . . . . 7-43





C H A P T E R 11.
VARIATION UNDER NATURE.
Variability - Individual differences - Doubtful species - Wide
ranging, much diffused, and common species vary m o s t S p e -
cies of the larger genera in any country vary niore tban the species
of the smaller genera-Many of the species of the larger genera
resemble varieties in being very closely, but unequally, related
. . . . 44-59
to each other, and in having restricted ranges
vi


CONTENTS.
C H A Y T E B 111.
STRUGGLE EXISTEHCY.
FOR
Bears on natural selection-The term used in a wide sense-Geo-
metrical powers of increase - napid iiicrcxse of naturalised
animals and plants-Nature of the checks to incrcase-Compe-
tition 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 be-
tween species of the same genus-The relation of organism to
,.
organism the most important of all relations Page 60-79



CHAPTER IV.
NATURASELECTION. I,
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 gcnerality of inter-
crosses between individuals of the same species -Circnmstancea
favourable and unfavourable to Natwal Selection, namely,
intercrossing, isolation, number of individuals - Slow action -
Extinction caused by Natural Selection -Divergence of Cha-
racter, 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 .. .. .. . . . . . . .. .. . . . . 80-130



C H A P T E R V.
LAWSOF VARIATION.
Effects of external conditions -Use and disuse, combined with
natural selection ; organs of flight and of vision - Acclimatisa-
tion -Correlation of growth -Compensation and economy of
growth -False correlations -Multiple, rudimenbary, 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 . .. .. .. 131-170
vii



CONTENTS.
C H A P T E R VI.
DIFFICULTIES ON THEORY.
Difficultieson 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
cxtrcme perfection-Means of transition-Cases of difficulty-
Natura non facit saltum-Organs of small importance-Organs
law of Unity of Type
not in all cases absolutely perfect-The
and of the Conditions of Existence embraced by the theory of
.. .. .. . . .. .. Page 171-206
Natural Selection



CHAPTER VII.
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 - Scmmary
207-244



CHAPTER VIII.
HYBRIDISM.
Distinction between the sterility of first crosses and of hybrids -
Sterility various in degree, not universal, affected by close inter-
breeding, 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 con-
ditions of life and crossing - Fertility of varieties when crossed
and of thcir mongrcl offspring not universal - Hybrids and
mongrels compared indelmndently of their fertility - Summary

On the origin of species by means of natural selection,: Or, The preservation of favoured races in the struggle for life

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