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On the Origin of Species

Charles Darwin


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On the Origin of Species by Charles Darwin was first published in 1859. The full title of the book is 'On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life'. Darwin's book, which shows evidence of life arising by common descent, and progressing and evolving over generations through natural selection, became the foundation of evolutionary biology. At the time the book was published, there was already growing support for the concept of evolution, but that also conflicted with the Church which at the time was very intertwined with the scientific establishment in England. One of the reasons the book was so popular was because Darwin wrote it not for scientists, but for general readers.

The book was delayed from 1839, and whilst various theories have been put forth for this (including Darwin's fears of religious persecution), it would seem that it was more a case of him wanting to get everything right. But in 1855, Alfred Russell Wallace published a paper which had claims regarding fossil species that seemed very close to the theories that Darwin was about to propose in On the Origin of Species. The Scottish geologist Charles Lyell urged Darwin to publish his book so as to establish priority.

Within two decades of the publication of On the Origin of Species, evolutionism was a mainstream scientific theory and the term Darwinism entered the English language. Full chapter list.

№ 3 in Neil deGrasse Tyson's Essential Book List.

№ 19 in Anne Haight's List of Banned Books.

Part of the Encyclopaedia Britannica’s Great Books of the Western World set.

This book has 321 pages in the PDF version, and was originally published in 1859. This text is from the 6th edition, first published in 1872.

Production notes: This ebook of On the Origin of Species was published by Global Grey on the 2nd September 2018 and updated on the 5th August 2021. The artwork used for the cover is 'A Macaque' by Charles Verlat.

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Excerpt from 'On the Origin of Species'

When we compare 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 more from each other than do the individuals of any one species or variety in a state of nature. And if 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, we are driven to conclude that this great variability is 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 species had been exposed under nature. There is, also, some probability in the view propounded by Andrew Knight, that this variability may be partly connected with excess of food. It seems clear that organic beings must be exposed during several generations to new conditions to cause any great amount of variation; and that, when the organisation has once begun to vary, it generally continues varying for many generations. No case is on record of a variable organism ceasing to vary under cultivation. Our oldest cultivated plants, such as wheat, still yield new varieties: our oldest domesticated animals are still capable of rapid improvement or modification.

As far as I am able to judge, after long attending to the subject, the conditions of life appear to act in two ways—directly on the whole organisation or on certain parts alone and in directly by affecting the reproductive system. With respect to the direct action, we must bear in mind that in every case, as Professor Weismann has lately insisted, and as I have incidently shown in my work on “Variation under Domestication,” there are two factors: namely, the nature of the organism and the nature of the conditions. The former seems to be much the more important; for nearly similar variations sometimes arise under, as far as we can judge, dissimilar conditions; and, on the other hand, dissimilar variations arise under conditions which appear to be nearly uniform. The effects on the offspring are either definite or in definite. They may be considered as definite when all or nearly all the offspring of individuals exposed to certain conditions during several generations are modified in the same manner. It is extremely difficult to come to any conclusion in regard to the extent of the changes which have been thus definitely induced. There can, however, be little doubt about many slight changes, such as size from the amount of food, colour from the nature of the food, thickness of the skin and hair from climate, &c. Each of the endless variations which we see in the plumage of our fowls must have had some efficient cause; and if the same cause were to act uniformly during a long series of generations on many individuals, all probably would be modified in the same manner. Such facts as the complex and extraordinary out growths which variably follow from the insertion of a minute drop of poison by a gall-producing insect, shows us what singular modifications might result in the case of plants from a chemical change in the nature of the sap.

In definite variability is a much more common result of changed conditions than definite variability, and has probably played a more important part in the formation of our domestic races. We see in definite variability in the endless slight peculiarities which distinguish the individuals of the same species, and which cannot be accounted for by inheritance from either parent or from some more remote ancestor. Even strongly-marked differences occasionally appear in the young of the same litter, and in seedlings from the same seed-capsule. At long intervals of time, out of millions of individuals reared in the same country and fed on nearly the same food, deviations of structure so strongly pronounced as to deserve to be called monstrosities arise; but monstrosities cannot be separated by any distinct line from slighter variations. All such changes of structure, whether extremely slight or strongly marked, which appear among many individuals living together, may be considered as the in definite effects of the conditions of life on each individual organism, in nearly the same manner as the chill effects different men in an in definite manner, according to their state of body or constitution, causing coughs or colds, rheumatism, or inflammation of various organs.

With respect to what I have called the in direct action of changed conditions, namely, through the reproductive system of being affected, we may infer that variability is thus induced, partly from the fact of this system being extremely sensitive to any change in the conditions, and partly from the similarity, as Kölreuter and others have remarked, between the variability which follows from the crossing of distinct species, and that which may be observed with plants and animals when reared under new or unnatural conditions. Many facts clearly show how eminently susceptible the reproductive system is to very slight changes in the surrounding conditions. Nothing is more easy than to tame an animal, and few things more difficult than to get it to breed freely under confinement, even when the male and female unite. How many animals there are which will not breed, though kept in an almost free state in their native country! This is generally, but erroneously attributed to vitiated instincts. Many cultivated plants display the utmost vigour, and yet rarely or never seed! In some few cases it has been discovered that a very trifling change, such as a little more or less water at some particular period of growth, will determine whether or not a plant will produce seeds. I cannot here give the details which I have collected and elsewhere published on this curious subject; but to show how singular the laws are which determine the reproduction of animals under confinement, I may 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, which seldom produce young; whereas, carnivorous birds, with the rarest exception, hardly ever lay fertile eggs. Many exotic plants have pollen utterly worthless, in the same condition as in the most sterile hybrids. When, on the one hand, we see domesticated animals and plants, though often weak and sickly, breeding 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 to act, we need not be surprised at this system, when it does act under confinement, acting irregularly, and producing offspring somewhat unlike their parents. I may add that as some organisms breed freely under the most unnatural conditions—for instance, rabbits and ferrets kept in hutches—showing that their reproductive organs are not easily affected; so will some animals and plants withstand domestication or cultivation, and vary very slightly—perhaps hardly more than in a state of nature.

Some naturalists have maintained that all variations are connected with the act of sexual reproduction; but this is certainly an error; for I have given in another work a long list of “sporting plants;” as they are called by gardeners; that is, of plants which have suddenly produced a single bud with a new and sometimes widely different character from that of the other buds on the same plant. These bud variations, as they may be named, can be propagated by grafts, offsets, &c., and sometimes by seed. They occur rarely under nature, but are far from rare under culture. As a single bud out of many thousands produced year after year on the same tree under uniform conditions, has been known suddenly to assume a new character; and as buds on distinct trees, growing under different conditions, have sometimes yielded nearly the same variety—for instance, buds on peach-trees producing nectarines, and buds on common roses producing moss-roses—we clearly see that the nature of the conditions is of subordinate importance in comparison with the nature of the organism in determining each particular form of variation; perhaps of not more importance than the nature of the spark, by which a mass of combustible matter is ignited, has in determining the nature of the flames.

Chapter List for 'On the Origin of Species'

Chapter 1. Variation Under Domestication
Causes of Variability - Effects of Habit and the use and 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 followed, their Effects - Methodical and Unconscious Selection - Unknown Origin of our Domestic Productions - Circumstances favourable to Man’s power of Selection.

Chapter 2. Variation Under Nature
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.

Chapter 3. Struggle For Existence
Its bearing on natural selection - The term used in a wide sense - Geometrical 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 relations.

Chapter 4. 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 of the same species - Circumstances favourable and unfavourable 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.

Chapter 5. 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.

Chapter 6. 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.

Chapter 7. 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 incompetence 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 disbelieving in great and abrupt modifications.

Chapter 8. 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, 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.

Chapter 9. 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, 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 fertility - Summary.

Chapter 10. 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 lapse of time, as inferred from the rate of denudation and of deposition number - On the lapse of time as estimated by years - On the poorness of our palæontological collections - On the intermittence of geological formations - On the denudation of granitic areas - 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 - Antiquity of the habitable earth.

Chapter 11. 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 12. 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 - Alternate Glacial periods in the North and South.

Chapter 13. 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 14. 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 15. Recapitulation And Conclusion
Recapitulation of the objections to 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.

Glossary Of The Principal Scientific Terms Used In The Present Volume.

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