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On the generality of intercrosses between individuals of the same species—Cir cumstances 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, ....... TT

CHAPTER V.

LAWS Of Y A R"I A T I O W .

Effects of external conditions—Use and disuse, combined with natural selection organs of flight and of vision—Acelimatisation—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, . . . . . 120

CHAPTER VI.

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 faclt saltum—Organs of small importance—Organs-irot in all cases absolutely perfect—The law of Unity of Type and of tho Conditions of Existence embraced by the theory of Natural Selection, ...... 1M

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 ante—Hive-bee, its cell-making instinct—Difficulties on tho theory of the Natural Selection of instincts—Neuter or sterile insects—Summary, . . . . .181

CHAPTER VIII.

HTBRIDISH.

Distinction betwecn,tho sterility of first crosses and of hybrids—Sterility various in degree, not universal, affected by close interbreeding, removed by domestication— Laws governing tho 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 tho effects of changed conditions of life and cross> lug—Fertility of varieties when crossed and of their mongrel offspring not uni versal—Hybrids and mongrels compared independently of their fertility—Summary ,217

CHAPTER IX.

OK THE IMPERFECTION 07 THE GEOLOGICAL RECORD.

On tho absence of intermediate varieties at the present day—On the nature of extinct Intermediate varieties j on their number—On the vast lapse of time, as inferred from the rate of deposition and of denudation—On the poorness of our palceontological collections—On the lntermlttenco 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, . 2U

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 tho 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 aud present chapters, .... 273

CHAPTER XI.

GEOGRApHICAL. DISTRIBUTION.

Present distribution cannot be accounted for by differences in physical conditions—Importance of barriers—Affinity of the productions of tho 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 802

CHAPTER XII.

aEOGRApniCAL Distrihl-tion— Continued.

Distribution of fresh-water [productions—On tho inhabitants of oceanic islands—Absence of Batrachlans and of terrestrial mammals—On tho relation of tho inhabitants of islands to those of the nearest mainland—On colonisation from the nearest source with subsequent modification—Summary of tho last and present chapters, Ki4

CHAPTER XIII.

BCTCAL AFFINITIES OF ORGANIC BEINGS I M0RpHOLO0T I EMBRTOLOGT: RUDIKEKTAET ORGANS.

Classification, groups subordinate to groups—Natural system—Rules and difficulties in ciassification, explained on the theory of descent with modification—Classi' float ion of varieties—Descent always used in classification—Analogical or adaptive characters—Affinities, general, complex and radiating—Extinction separates and defines groups—MoRpbOLOor, between members of tho same class, between parts of the same individual —Embrtoloor, laws of, explained by variations not supervening at an early age, and being inherited at a corresponding age —Rudimintart OMUI; their origin explained—Summary, . . . . .351

CHAPTER XIV.

RKCAPITtJLATION AND CONCLUSION.

Recapitulation of the difficulties on tho theory of Natural Selection—Recapitulation of the general and special circumstances in its favour—Causes of tho 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, .......... 898

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ON THE ORIGIN OF SPECIES.

INTRODUCTION.

When on board H. M. S. 1 Beagle' as naturalist, I was
much struck with certain facts in the distribution of the
inhabitants of South America, and in the geological rela-
tions of the present to the past inhabitants of that con-
tinent. These facts seemed to me to throw some light
on the origin of species—that mystery of mysteries, as it
has been called by one of our greatest philosophers. On
my return home, it occurred to me, in 1837, that some-
thing might perhaps be made out on this question by
patiently accumulating and reflecting on all sorts of facts
which could possibly have any bearing on it. After five
years' work I allowed myself to speculate on the subject,
and drew up some short notes; these I enlarged in 1844
into a sketch of the conclusions, which then seemed to me
probable: from that period to the present day I have stead-
ily pursued the same object. I hope that I may be ex-
cused for entering on these personal details, as I give
them to show that I have not been hasty in coming to a
decision.

My work is now nearly finished; but as it will take
me two or three more years to complete it, and as my
health is far from strong, I have been urged to publish
this" Abstract. I have more especially been induced to
do this, as Mr. Wallace, who is now studying the natural
history of the Malay archipelago, has arrived at almost
exactly the same general conclusions that I have on the
origin of species. Last year he sent to me a memoir on
this subject, with a request that I would forward it to Sir
Charles Lyell, who sent it to the Linnean Society, and it

Society. Sir C. Lyell and Dr. Hooker, who both knew
of my work—the latter having read my sketch of 1844
—honoured me by thinking it advisable to publish,
with Mr. Wallace's excellent memoir, some brief extracts
from my manuscripts.

This Abstract, which I now publish, must necessarily
be imperfect. I cannot here give references and author-
ities for my several statements; and I must trust to the
reader reposing some confidence in my accuracy. No
doubt errors will have crept in, though I hope I have
always been cautious in trusting to good authorities alone.
I can here give only the general conclusions at which I
have arrived, with a few facts in illustration, but which,
I hope, in most cases will suffice. No one can feel more
sensible than I do of the necessity of hereafter publishing
in detail all the facts, with references, on which my con-
clusions have been grounded; and I hope in a future work
to do this. For I am well aware that scarcely a single
point is discussed in this volume on which facts cannot
be adduced, often apparently leading to conclusions di-
rectly opposite to those at which I have arrived. A fair
result can be obtained only by fully stating and balancing
the facts and arguments on both sides of each question;
and this cannot possibly be here done.

I much regret that want of space prevents my having
the satisfaction of acknowledging the generous assistance
which I have received from very many naturalists, some
of them personally unknown to me. I cannot, however,
let this opportunity pass without expressing my deep
obligations to Dr. Hooker, who for the last fifteen years
has aided me in every possible way by his large stores of
knowledge and his excellent judgment.

In considering the Origin of Species, it is quite con-
ceivable that a naturalist, reflecting on the mutual affini-
ties of organic beings, on their embryological relations,
their geographical distribution, geological succession, and
other such facts, might come to the conclusion that each
species had not been independently created, but had de-

is published in the third volume

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