The origin of species by natural selection, or the conservation of races favoured in the struggle for life.

By

Charles Darwin

Graduated in Humanity, member of the Royal, Geological, Linnean Societies, etc.

Author of the diary or the researches during the trip around the world aboard  Beagle, his Majesty’s ship.

London
John Murray, Albemarle Street.
1859

Introduction

When I was on board the Beagle as a naturalist, I was surprised related to the distribution of living creatures in South America and the geological relations of the inhabitants of this continent with respect of the past. It seemed to me that these facts illuminated a little the origin of the species. When I returned home, it occurred to me, in 1837, that maybe something could deduce from patiently accumulating and of thinking about all kinds of facts that progress to have some bond. After five years of work I allowed myself to speculate about the subject and to outline some short notes. From this period until the present day I have pursued same objective with firmness.

Now [1859], my work is practically finished; but, as it will take me two or three more years to complete it and my health is far from good, I have been urged to publish this summary. I have been prompted above all the facts that Mr. Wallace, who is currently studying the natural history of the Malay Archipelago, has reached almost exactly the same conclusion as I have about the origin of the species. In July 1858 he sent me a study with the request that I forward it to Sir Charles Lyell, who in turn sent to the Linnean Society, and it was published in the third volume of the Linnean Society magazine. Sir C. Lyell and Dr. Hooker thought it advisable to publish, together with Wallace’s excellent work, some brief extracts from my manuscripts.

By force, this summary will be imperfect. Here I cannot give references about my statements; only the general conclusions I have reached, with a few facts to illustrate them but I hope will be sufficient in most cases.

When considering the origin of the species, it is quite reasonable that a naturalist, reflecting on the mutual affinities of organic beings, their embryological relationships, geographical distribution, geological succession and other related facts, may come to the conclusion that each species has not been created independently, but has descended, like varieties, other species. Even so, such a conclusion, even if founded, would be unsatisfactory as long as it could not be demonstrated how the innumerable species that inhabit this world have been modified to acquire the perfection of structure and coadaptation that so rightly cause our admiration.

Naturalists continually refer to external conditions, such as climate, food, etc., as the only possible causes of variation. In a very limited sense this may be true, as we will see later. But it is nonsense to attribute to the external conditions the structure of the woodpecker-for example- with its legs, tail, beak and tongue, so admirably adapted to catch insects under the bark of trees, In case of mistletoe, which takes  its food from certain trees, which are then transported by certain birds and flowers with separate sexes that need the action of the insects to bring pollen from one flower to another, it is also an absurdity to explain the structure of this parasite and its relations with other organic beings by the effects of external conditions, or by the habits or by the will of the plant itself.

I imagine that the author of Vestiges of Creation would say that, after a certain number of generations, some bird would have given rise to the woodpecker and some plant, to mistletoe. And that the two would have been produced perfect as we know them today. But this presupposition is no explanation for me, since it neither touches nor explains the case of the adaptations of organic beings between them and with respect to each other's living conditions.

It is therefore of the greatest importance to understand very well the means of modification and coadaptation. At the beginning of my observations it seemed probable that a meticulous study of domestic animals and cultivated plants would offer the best opportunity to clarify this dark problem. I can venture to express my conviction of the great value of such studies, although naturalists have often ignored them.

For all these considerations, I will dedicate the first chapter of this summary to variation in domestic state. I will continue later with the variability of species in their natural state. The following chapter will deal with the struggle for existence among organic beings throughout the world, which inevitably derives from the geometric progression with which they multiply. This is the doctrine of Malthus, applied to the whole of the animal and plant kingdoms. How many more individuals are born in each species than can survive; and how, consequently, there is a recurrent struggle for existence, it follows that if any organism experiences any variation, however slight, which is profitable to it in the complex and sometimes changing conditions of life, it will have many more chances of surviving and, therefore, of being selected naturally. From the strong principle of heredity, any selected variety will tend to propagate its new modified form.

This fundamental matter of natural selection will be dealt with to some extent in the fourth chapter; and we will see how natural selection causes, almost inevitably, much of the extinction of the less improved forms and leads to the divergence of characters. In the following chapters the most obvious and serious difficulties of the theory will be exposed, and I will consider the geological succession of organic beings over time, as well as their geographical distribution throughout space. In the last chapter I will give a brief recapitulation of all the work and some notes in the guise of conclusion.

Although there continue to be many dark spots - and dark spots will continue for a long time - I have no doubt that the belief that most naturalists maintain, and that I myself had maintained, is erroneous: that each species was created independently. I am fully convinced that species are not immutable but that those belonging to what has been called the same genus are direct descendants of other species, generally extinct, just as the recognized varieties of any species are the descendants of this one. Furthermore, I am convinced that natural selection has been the main means of modification, but not the exclusive one.