ON

THE ORIGIN OF SPECIES

BY

MEANS OF NATURAL SELECTION,

OR THE

PRESERVATION OF FAVORED RACES IN THE STRUGGLE
FOR LIFE.

BY

CHARLES DARWIN, M. A., F. R. S.,

66

AUTHON OF JOURNAL OF RESEARCHES DURING H. M. S. BEAGLE'S VOYAGE ROUND
THE WORLD," ETC., ETC.

NEW EDITION, FROM THE SIXTH ENGLISH EDITION, WITH ADDITIONS
AND CORRECTIONS.

NEW YORK :

D. APPLETON AND COMPANY,
1, 3, AND 5 BOND STREET.

1888.

SCIENC
QH
365
.02.
18886
Copy!

But with regard to the material world, we can at least go so far a 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."

WHEWELL: Bridgewater Treatise.

"The only distinct meaning of the word 'natural' is stated, fixed, or settled; since what is natural as much requires and presupposes an intelligent agent to render it so, i. e., to effect it continually or at stated times, as what is supernatural or miraculous does to effect it for once."

BUTLER: Analogy of Revealed Religion.

"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."

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Causes of Variability-Effects of Habit and 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- Domestic Pigeons,

their Differences and Origin - Principles of Selection, anciently fol-

lowed, their Effects - Methodical and Unconscious Selection

known Origin of our Domestic Productions - Circumstances favour-

able to Man's power of Selection

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CHAPTER II.

VARIATION UNDER NATURE.

-

-Un-

5-32

Variability 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 of the larger genera resemble

varieties in being very closely, but unequally, related to each other,

and in having restricted ranges

33-47

CHAPTER III.

STRUGGLE FOR EXISTENCE.

-

Its bearing on natural selection - The term used in a wide sense-Geome

trical ratio 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 rela-

tions

48-61

CHAPTER IV.

NATURAL SELECTION; OR THE SURVIVAL OF THE FITTEST.

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 cf the same species-Circumstances favourable and unfa-

vourable to the results of 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 Advance in organisation - Low forms preserved

Convergence of character-Indefinite multiplication of species-

Summary

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..

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Page 62-105

CHAPTER V.

LAWS OF VARIATION.

Effects of changed conditions- Use and disuse, combined with natural

selection; organs of flight and of vision - Acclimatisation - Correlated

variation-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

106-132

CHAPTER VI.

DIFFICULTIES OF THE THEORY.

-

Difficulties of the theory of descent with modification 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 Modes 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
133-167

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CHAPTER VII.

MISCELLANEOUS OBJECTIONS TO THE THEORY OF NATURAL

SELECTION.

Longevity - Modifications not necessarily simultaneous - Modifications

apparently of no direct service-Progressive development-Characters

of small functional importance, the most constant-Supposed incom-

petence of natural selection to account for the incipient stages of

useful structures-Causes which interfere with the acquisition through

natural selection of useful structures-Gradations of structure with

changed functions-Widely different organs in members of the same

class, developed from one and the same source-Reasons for disbeliev-

ing in great and abrupt modifications

Page 168-204

CHAPTER VIII.

INSTINCT.

Instincts comparable with habits, but different in their origin-Instincts

graduated - Aphides and ants - Instincts variable-Domestic in-

stincts, their origin — Natural instincts of the cuckoo, molothrus,

ostrich, and parasitic bees-Slave-making ants Hive-bee, its cell-

making instinct-Changes of instinct and structure not necessarily

simultaneous-Difficulties of the theory of the Natural Selection of

instincts - Neuter or sterile insects

-

- Summary

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205-234

CHAPTER IX.

HYBRIDISM..

Distinction between the sterility of first crosses and of hybrids — Sterility

various in degree, not universal, affected by close interbreeding, re-

moved by domestication-Laws governing the sterility of hybrids —

Sterility not a special endowment, but incidental on other differences,

not accumulated by natural selection - Causes of the sterility of first

crosses and of hybrids - Parallelism between the effects of changed

conditions of life and of crossing - Dimorphism and Trimorphism —

Fertility of varieties when crossed and of their mongrel offspring not

universal — Hybrids and mongrels compared independently of their

tertility Summary

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234-263