On the Origin of Species
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.

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On the Origin of Species by Means of Natural Selection, or the Preservation of
Favoured Races in the Struggle for Life.
By Charles Darwin
Contents
Introduction
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.
Chapter IV
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.

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Chapter V
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 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 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 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 -- Summary.
Chapter VIII 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 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

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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: Morphology: Embryology: Rudimentary
Organs
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 Conclusion
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

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-- 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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On the Origin of Species.
Introduction.
When on board H.M.S. 'Beagle,' as naturalist, I was much struck with certain facts in the
distribution of the inhabitants of South America, and in the geological relations of the present to the
past inhabitants of that continent. 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 something 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 steadily pursued the same object. I hope
that I may be excused 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 is published in the third volume of the
Journal of that 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 authorities 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 conclusions 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 directly 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 conceivable that a naturalist, reflecting on the
mutual affinities of organic beings, on their embryological relations, their geographical distribution,

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geological succession, and other such facts, might come to the conclusion that each species had not
been independently created, but had descended, like varieties, from other species. Nevertheless,
such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how the
innumerable species inhabiting this world have been modified, so as to acquire that perfection of
structure and coadaptation which most justly excites our admiration. Naturalists continually refer
to external conditions, such as climate, food, &c., as the only possible cause of variation. In one
very limited sense, as we shall hereafter see, this may be true; but it is preposterous to attribute to
mere external conditions, the structure, for instance, of the woodpecker, with its feet, tail, beak, and
tongue, so admirably adapted to catch insects under the bark of trees. In the case of the misseltoe,
which draws its nourishment from certain trees, which has seeds that must be transported by certain
birds, and which has flowers with separate sexes absolutely requiring the agency of certain insects
to bring pollen from one flower to the other, it is equally preposterous to account for the structure
of this parasite, with its relations to several distinct organic beings, by the effects of external
conditions, or of habit, or of the volition of the plant itself.
The author of the 'Vestiges of Creation' would, I presume, say that, after a certain unknown number
of generations, some bird had given birth to a woodpecker, and some plant to the misseltoe, and
that these had been produced perfect as we now see them; but this assumption seems to me to be no
explanation, for it leaves the case of the coadaptations of organic beings to each other and to their
physical conditions of life, untouched and unexplained.
It is, therefore, of the highest importance to gain a clear insight into the means of modification and
coadaptation. At the commencement of my observations it seemed to me probable that a careful
study of domesticated animals and of cultivated plants would offer the best chance of making out
this obscure problem. Nor have I been disappointed; in this and in all other perplexing cases I have
invariably found that our knowledge, imperfect though it be, of variation under domestication,
afforded the best and safest clue. I may venture to express my conviction of the high value of such
studies, although they have been very commonly neglected by naturalists.
From these considerations, I shall devote the first chapter of this Abstract to Variation under
Domestication. We shall thus see that a large amount of hereditary modification is at least possible,
and, what is equally or more important, we shall see how great is the power of man in accumulating
by his Selection successive slight variations. I will then pass on to the variability of species in a
state of nature; but I shall, unfortunately, be compelled to treat this subject far too briefly, as it can
be treated properly only by giving long catalogues of facts. We shall, however, be enabled to
discuss what circumstances are most favourable to variation. In the next chapter the Struggle for
Existence amongst all organic beings throughout the world, which inevitably follows from their
high geometrical powers of increase, will be treated of. This is the doctrine of Malthus, applied to
the whole animal and vegetable kingdoms. As many more individuals of each species are born
than can possibly survive; and as, consequently, there is a frequently recurring struggle for
existence, it follows that any being, if it vary however slightly in any manner profitable to itself,
under the complex and sometimes varying conditions of life, will have a better chance of surviving,
and thus be naturally selected. From the strong principle of inheritance, any selected variety will
tend to propagate its new and modified form.
This fundamental subject of Natural Selection will be treated at some length in the fourth chapter;
and we shall then see how Natural Selection almost inevitably causes much Extinction of the less

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improved forms of life and induces what I have called Divergence of Character. In the next chapter
I shall discuss the complex and little known laws of variation and of correlation of growth. In the
four succeeding chapters, the most apparent and gravest difficulties on the theory will be given:
namely, first, the difficulties of transitions, or in understanding how a simple being or a simple
organ can be changed and perfected into a highly developed being or elaborately constructed organ;
secondly the subject of Instinct, or the mental powers of animals, thirdly, Hybridism, or the
infertility of species and the fertility of varieties when intercrossed; and fourthly, the imperfection
of the Geological Record. In the next chapter I shall consider the geological succession of organic
beings throughout time; in the eleventh and twelfth, their geographical distribution throughout
space; in the thirteenth, their classification or mutual affinities, both when mature and in an
embryonic condition. In the last chapter I shall give a brief recapitulation of the whole work, and a
few concluding remarks.
No one ought to feel surprise at much remaining as yet unexplained in regard to the origin of
species and varieties, if he makes due allowance for our profound ignorance in regard to the mutual
relations of all the beings which live around us. Who can explain why one species ranges widely
and is very numerous, and why another allied species has a narrow range and is rare? Yet these
relations are of the highest importance, for they determine the present welfare, and, as I believe, the
future success and modification of every inhabitant of this world. Still less do we know of the
mutual relations of the innumerable inhabitants of the world during the many past geological
epochs in its history. Although much remains obscure, and will long remain obscure, I can
entertain no doubt, after the most deliberate study and dispassionate judgment of which I am
capable, that the view which most naturalists entertain, and which I formerly entertained--namely,
that each species has been independently created--is erroneous. I am fully convinced that species
are not immutable; but that those belonging to what are called the same genera are lineal
descendants of some other and generally extinct species, in the same manner as the acknowledged
varieties of any one species are the descendants of that species. Furthermore, I am convinced that
Natural Selection has been the main but not exclusive means of modification.
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.
When we look to the individuals of the same variety or sub-variety of our older cultivated plants
and animals, one of the first points which strikes us, is, that they generally differ much more from
each other, than do the individuals of any one species or variety in a state of nature. When we
reflect on the vast diversity of the plants and animals which have been cultivated, and which have
varied during all ages under the most different climates and treatment, I think we are driven to
conclude that this greater variability is simply due to our domestic productions having been raised
under conditions of life not so uniform as, and somewhat different from, those to which the parent-

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species have been exposed under nature. There is, also, I think, some probability in the view
propounded by Andrew Knight, that this variability may be partly connected with excess of food.
It seems pretty clear that organic beings must be exposed during several generations to the new
conditions of life to cause any appreciable amount of variation; and that when the organisation has
once begun to vary, it generally continues to vary for many generations. No case is on record of a
variable being ceasing to be variable under cultivation. Our oldest cultivated plants, such as wheat,
still often yield new varieties: our oldest domesticated animals are still capable of rapid
improvement or modification.
It has been disputed at what period of life the causes of variability, whatever they may be, generally
act; whether during the early or late period of development of the embryo, or at the instant of
conception. Geoffroy St. Hilaire's experiments show that unnatural treatment of the embryo causes
monstrosities; and monstrosities cannot be separated by any clear line of distinction from mere
variations. But I am strongly inclined to suspect that the most frequent cause of variability may be
attributed to the male and female reproductive elements having been affected prior to the act of
conception. Several reasons make me believe in this; but the chief one is the remarkable effect
which confinement or cultivation has on the functions of the reproductive system; this system
appearing to be far more susceptible than any other part of the organisation, to the action of any
change in the conditions of life. Nothing is more easy than to tame an animal, and few things more
difficult than to get it to breed freely under confinement, even in the many cases when the male and
female unite. How many animals there are which will not breed, though living long under not very
close confinement in their native country! This is generally attributed to vitiated instincts; but how
many cultivated plants display the utmost vigour, and yet rarely or never seed! In some few such
cases it has been found out that very trifling changes, such as a little more or less water at some
particular period of growth, will determine whether or not the plant sets a seed. I cannot here enter
on the copious details which I have collected on this curious subject; but to show how singular the
laws are which determine the reproduction of animals under confinement, I may just mention that
carnivorous animals, even from the tropics, breed in this country pretty freely under confinement,
with the exception of the plantigrades or bear family; whereas, carnivorous birds, with the rarest
exceptions, hardly ever lay fertile eggs. Many exotic plants have pollen utterly worthless, in the
same exact condition as in the most sterile hybrids. When, on the one hand, we see domesticated
animals and plants, though often weak and sickly, yet breeding quite freely under confinement; and
when, on the other hand, we see individuals, though taken young from a state of nature, perfectly
tamed, long-lived, and healthy (of which I could give numerous instances), yet having their
reproductive system so seriously affected by unperceived causes as to fail in acting, we need not be
surprised at this system, when it does act under confinement, acting not quite regularly, and
producing offspring not perfectly like their parents or variable.
Sterility has been said to be the bane of horticulture; but on this view we owe variability to the
same cause which produces sterility; and variability is the source of all the choicest productions of
the garden. I may add, that as some organisms will breed most freely under the most unnatural
conditions (for instance, the rabbit and ferret kept in hutches), showing that their reproductive
system has not been thus affected; so will some animals and plants withstand domestication or
cultivation, and vary very slightly--perhaps hardly more than in a state of nature.
A long list could easily be given of 'sporting plants;' by this term gardeners mean a single bud or
offset, which suddenly assumes a new and sometimes very different character from that of the rest

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of the plant. Such buds can be propagated by grafting, &c., and sometimes by seed. These 'sports'
are extremely rare under nature, but far from rare under cultivation; and in this case we see that the
treatment of the parent has affected a bud or offset, and not the ovules or pollen. But it is the
opinion of most physiologists that there is no essential difference between a bud and an ovule in
their earliest stages of formation; so that, in fact, 'sports' support my view, that variability may be
largely attributed to the ovules or pollen, or to both, having been affected by the treatment of the
parent prior to the act of conception. These cases anyhow show that variation is not necessarily
connected, as some authors have supposed, with the act of generation.
Seedlings from the same fruit, and the young of the same litter, sometimes differ considerably from
each other, though both the young and the parents, as Muller has remarked, have apparently been
exposed to exactly the same conditions of life; and this shows how unimportant the direct effects of
the conditions of life are in comparison with the laws of reproduction, and of growth, and of
inheritance; for had the action of the conditions been direct, if any of the young had varied, all
would probably have varied in the same manner. To judge how much, in the case of any variation,
we should attribute to the direct action of heat, moisture, light, food, &c., is most difficult: my
impression is, that with animals such agencies have produced very little direct effect, though
apparently more in the case of plants. Under this point of view, Mr. Buckman's recent experiments
on plants seem extremely valuable. When all or nearly all the individuals exposed to certain
conditions are affected in the same way, the change at first appears to be directly due to such
conditions; but in some cases it can be shown that quite opposite conditions produce similar
changes of structure. Nevertheless some slight amount of change may, I think, be attributed to the
direct action of the conditions of life--as, in some cases, increased size from amount of food, colour
from particular kinds of food and from light, and perhaps the thickness of fur from climate.
Habit also has a deciding influence, as in the period of flowering with plants when transported from
one climate to another. In animals it has a more marked effect; for instance, I find in the domestic
duck that the bones of the wing weigh less and the bones of the leg more, in proportion to the
whole skeleton, than do the same bones in the wild-duck; and I presume that this change may be
safely attributed to the domestic duck flying much less, and walking more, than its wild parent.
The great and inherited development of the udders in cows and goats in countries where they are
habitually milked, in comparison with the state of these organs in other countries, is another
instance of the effect of use. Not a single domestic animal can be named which has not in some
country drooping ears; and the view suggested by some authors, that the drooping is due to the
disuse of the muscles of the ear, from the animals not being much alarmed by danger, seems
probable.
There are many laws regulating variation, some few of which can be dimly seen, and will be
hereafter briefly mentioned. I will here only allude to what may be called correlation of growth.
Any change in the embryo or larva will almost certainly entail changes in the mature animal. In
monstrosities, the correlations between quite distinct parts are very curious; and many instances are
given in Isidore Geoffroy St. Hilaire's great work on this subject. Breeders believe that long limbs
are almost always accompanied by an elongated head. Some instances of correlation are quite
whimsical; thus cats with blue eyes are invariably deaf; colour and constitutional peculiarities go
together, of which many remarkable cases could be given amongst animals and plants. From the
facts collected by Heusinger, it appears that white sheep and pigs are differently affected from
coloured individuals by certain vegetable poisons. Hairless dogs have imperfect teeth; long-haired

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Document Outline

• On the Origin of Species
• Contents
• Chapter I Introduction.
• Chapter II Variation Under Nature
• Chapter III Struggle for Existence
• Chapter IV Natural Selection
• Chapter V. Laws of Variation
• Chapter VI Difficulties on Theory
• Chapter VII Instinct
• Chapter VIII Hybridism
• Chapter IX On the Imperfection of the Geological Record
• Chapter X On the Geological Succession of Organic Beings
• Chapter XI Geographical Distribution
• Chapter XII Geographical Distribution--
• Chapter XIII Mutual Affinities of Organic Beings: Morphology: Embryology: RudimentaryOrgans
• Chapter XIV Recapitulation and Conclusion
• Subject Index

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