DARWIN "ORIGIN OF SPECIES"
For the first time, Darwin had the idea to investigate the question of the origin of now living species of animals and plants during a trip around the world on the British ship Beagle. Some phenomena in the geographical distribution of organic beings attracted his special attention, namely, the close relationship of a number of the living inhabitants of South America with extinct animals found in the additions of the same continent. Darwin became convinced that these phenomena could only be explained by assuming that living beings, however greatly altered, were descended from those that existed before, and that the law of the constancy or immutability of species, a law recognized by all the luminaries of natural science, was thus that time is unfair.
Turning to the study of the variability of domestic animals (pigeons) and cultivated plants under the influence of artificial selection, Darwin collected with great discretion an endless series of facts that served him as fulcrum for further study of variability. Based on these facts, he decided that in living nature there must be an engine that, acting like artificial selection, preserves from among the varieties of animals and plants freely formed everywhere such especially characteristic forms that outlive the rest. Convinced that this principle was found in "natural selection" as a result of the "struggle for existence", Darwin did not publicly express his views and, perhaps, would not have published his work for a long time if his friends Lyell and Hooker had not prompted him in the summer of 1858 to the publication of a work on the origin of species that he had written long ago and had long been known to a narrow circle of like-minded people. The reason for the publication was the fact that the traveler W. R. Wallace was going to publish his views, which were very similar to those of Darwin.
Darwin's influence on natural science was so great that he was called "Copernicus or Newton of the organic world." In the course of a few decades, the only revolution in the views, methods and goals of natural scientists, both botanists and zoologists, took place in the history of the study of the organic world. By declaring man a member of living nature, Darwin brought the sciences of man into interaction with the natural sciences, and thus the genetic method, the study of what is being created and developing in order to better understand what has been created, became the basis of the most diverse fields of knowledge. He had the rare happiness of seeing the complete triumph of his teaching. He found his first adherents and ardent admirers mainly in Germany.
Stormy, at first not free from personal attacks, the struggle with Darwin of his opponents has long subsided. Even his most ardent enemies were disarmed by the mild and peaceful form with which he defended his views. But with even greater success he conquered the minds with the strength and depth of his mind, the caution that never left him when evaluating his own conclusions. And he won hearts with his gentleness and justice in his judgments, his devotion to friends and sincere modesty in relation to his merits:
It is curious to contemplate the densely overgrown coast, covered with numerous, diverse plants, with birds singing in the bushes, insects fluttering around, worms crawling in the damp earth, and to think that all these beautifully built forms, so different from one another and so intricately dependent on one another , were created thanks to the laws that are still operating around us. These laws, in the broadest sense: Growth and Reproduction, Heredity, which almost necessarily follows from reproduction, Variability, depending on the direct or indirect action of living conditions and on use and disuse, A progression of increase in numbers so high that it leads to the Struggle for Life and its consequence - Natural Selection, which entails the Divergence of signs and the Extinction of less improved forms. Thus, from the struggle in nature, from hunger and death, the highest result that the mind can imagine, the formation of higher animals, directly follows. There is greatness in this view, according to which the Creator originally breathed life with its various manifestations into one or a limited number of forms; and while our planet continues to revolve according to the immutable laws of gravity, from such a simple beginning, an infinite number of the most beautiful and most marvelous forms have developed and continue to develop.
No one should be surprised that much concerning the origin of species still remains unexplained, if only one is aware of the deep ignorance in which we are in relation to the interconnection of the innumerable living beings around us. Who will explain why one species is widespread and represented by numerous individuals, while the other is not widespread and rare? And yet, these relationships are extremely important, as they determine the current welfare and, I believe, the future success and further change of every inhabitant of this world. We know even less about the mutual relations of the innumerable inhabitants of our planet during past geological epochs and its history. Although much is still obscure and will remain obscure for a long time, but as a result of the most careful study and impartial discussion that I am capable of, I have no doubt that the view, until recently shared by the majority of naturalists and which was also mine, namely, that everyone the species was created independently of the rest, that this view is wrong. I am fully convinced that species are variable, and that all species belonging to the same genus, the direct descendants of one of some, for the most part extinct species, just as the recognized varieties of one of some species, are considered descendants of this species. And further, I am convinced that natural selection was the most important, though not the only, factor by which this change was brought about.
Research by N. I. Vavilov and his school (the law of homological series of hereditary variability, the theory of Linnaean species), S. S. Chetverikov and his students (experimental population genetics), R. A. Fisher, S. Wright, J. Haldane, A I. Kolmogorov (mathematical theory of populations) I. I. Schmalhausen, B. Rensch, J. G. Simpson (patterns of macroevolution), O. Klineshmidt, E. Mayr, N. V. Timofeev-Ressovsky (species theory), F G. Dobzhansky (the doctrine of the isolating mechanisms of evolution), G. F. Gause and V. Volterra (the mathematical theory of selection) created the prerequisites for the formation in the 30s of the XX century of the “synthetic theory of evolution”, combining the achievements of Darwinism and modern genetics. This theory was accepted by the vast majority of natural scientists in the 1940s. Classical Darwinism entered the synthetic theory of evolution as an essential component. The latest discoveries in the field of molecular biology significantly modify the concept of modern Darwinism.
Summing up his life, Darwin himself half-jokingly described it as follows: "I studied, then traveled around the world, and then studied again: here is my biography." It would be nice if everyone lived such a life!
If, under changing conditions of life, organic beings show individual differences in almost every part of their organization, and this cannot be disputed; if, due to the geometric progression of reproduction, a fierce struggle for life is tied up at any age, in any year or season, and this, of course, cannot be disputed; and also if we remember the infinite complexity of the relations of organisms both among themselves and to their living conditions, and the infinite variety of useful features of structure, constitution and habits arising from these relations - if we take all this into account, it would be extremely improbable that never changes beneficial to the organism possessing them were manifested, in the same way as numerous changes beneficial to man arose. But if changes beneficial to any organism ever appear, the organisms possessing them will, of course, have the best chance of remaining in the struggle for life, and, by virtue of the strict principle of heredity, they will show a tendency to transmit them to posterity. This principle of conservation, or survival of the fittest, I have called Natural Selection. It leads to the improvement of every being in relation to the organic and inorganic conditions of his life, and consequently, in most cases, to what may be considered an ascent to a higher level of organization. Nevertheless, simply organized, lower forms will last long, if only they are well adapted to their simple living conditions.
Natural selection, based on the principle of inheritance of traits at an appropriate age, can change an egg, a seed, or a young organism as easily as an adult organism. In many animals, sexual selection has probably aided ordinary selection by ensuring that the strongest and best-adapted males have the most numerous offspring. Sexual selection also develops traits that are exclusively useful to males in their struggle or rivalry with other males, and these traits, depending on the predominant form of heredity, will be transmitted to both sexes or only one. Natural selection also leads to a divergence of characters, because the more organic beings differ in structure, habits and constitution, the greater their number can exist in a given area - proof of which we can find by paying attention to the inhabitants of any small piece of land and to organisms naturalized in a foreign country.
Natural selection, as has just been noted, leads to a divergence of characters and a significant extermination of less improved and intermediate forms of life. On the basis of these principles, both the nature of affinity and the usual presence of well-marked boundaries between innumerable organic beings of every class throughout the world can be easily explained. Truly amazing is the fact - although we are not amazed at it, it is so common - that all animals and all plants at all times and everywhere are connected in groups subordinate to one another, as we observe at every step, and just so that varieties of the same species are most closely related to each other; less closely and unevenly related species of the same genus, forming divisions and subgenera; even less close are the species of different genera and, finally, the genera, representing various degrees of mutual proximity, expressed by subfamilies, families, orders, subclasses and classes.
If the species were created independently of one another, then it would be impossible to find an explanation for this classification; but it is explained by heredity and the complex action of natural selection, which entails extinction and divergence of characters, as shown in our diagram.
The affinity of all beings belonging to the same class is sometimes depicted in the form of a large tree. I think this comparison is very close to the truth. The green, budding branches represent extant species, while those from previous years correspond to a long line of extinct species. In each period of growth, all growing branches form shoots in all directions, trying to overtake and drown out neighboring shoots and branches; in the same way, species and groups of species have at all times overpowered other species in the great struggle for life. The ramifications of the trunk, dividing at their ends first into large branches, and then into smaller and smaller branches, were themselves once - when the tree was still young - shoots dotted with buds; and this connection of former and modern buds, by means of branching branches, perfectly presents to us the classification of all modern and extinct species, which unites them into groups subordinate to other groups. Of the many shoots that sprang up before the tree had yet grown into a trunk, perhaps only two or three survived and have now grown into large branches that carry the rest of the branches; so it was with the species that lived in long past geological periods - only a few of them still living today left behind changed descendants.
Since the beginning of the life of this tree, many more and less large branches withered and fell off; these fallen branches of various sizes represent entire orders, families and genera, which at present do not have living representatives and are known to us only from fossil remains. Here and there, in a fork between the old branches, a scrawny shoot breaks out, survived by chance and still green at its top: such is some Ornithorhynchus or Lepidosiren, to some extent connecting by their affinity two large branches of life and saved from a fatal competition thanks to a protected habitat. As buds, by virtue of growth, give rise to new buds, and these, if only strong, turn into shoots, which, branching, cover and drown out many withered branches, so, I believe, it was also with the great Tree of Life, which filled its dead fallen branches of the bark of the earth and covered its surface with their ever-spreading and beautiful branches.
Comments
The position of the eyes in such semi-aquatic animals as the hippopotamus, the crocodile, and the frog is extremely similar: it is convenient for observing above the water when the body is immersed in water. However, convergent similarity in one trait does not affect most other organizational features, and the hippopotamus remains a typical mammal, the crocodile is a reptile, and the frog is an amphibian. In evolution, the re-emergence of individual features is possible (caused by a similarly directed action of natural selection, but the emergence of unrelated forms that are the same throughout their organization is impossible (the rule of irreversible evolution).
The convergence of traits, caused by a similar direction of natural selection, when it is necessary to live in some kind of similar environment, sometimes leads to surprising similarities. Sharks, dolphins and some ichthyosaurs are very similar in body shape. Some cases of convergence still mislead researchers. So, until the middle of the XX century. hares and rabbits were assigned to the same order of rodents on the basis of similarities in the structure of their dental systems. Only detailed studies of the internal organs, as well as biochemical features, made it possible to establish that hares and rabbits should be separated into an independent order of lagomorphs, phylogenetically closer to ungulates than to rodents.
The specificity of the genetic program of each organism is determined by the sequence of links in the DNA chain - nucleotides. The more similar (homologous) DNA sequences are, the more closely related organisms are. In molecular biology, methods have been developed to quantify the percentage of homology in DNA. So, if the presence of DNA homology among humans is taken as 100%, humans and chimpanzees will have about 92% homology. Not all homology values occur with the same frequency.
The figure shows the discreteness of the degrees of kinship in vertebrates. The lowest percentage of homology characterizes the DNA of representatives of different classes (1) such as birds - reptiles (lizard, turtles), fish and amphibians (5-15% homology). From 15 to 45% DNA homology in representatives of different orders within the same class (2), 50-75% in representatives of different families within the same order (3). If the compared forms belong to the same family, their DNA contains from 75 to 100% homology (4). Similar distribution patterns have been found in the DNA of bacteria and higher plants, but the numbers are quite different. According to DNA divergence, the genus of bacteria corresponds to the order, and even the class of vertebrates. When V. V. Menshutkin (I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry) simulated the process of loss of homology in DNA on a computer, it turned out that such distributions arise only if evolution proceeds according to Darwin - by selecting extreme options with the extinction of intermediate forms.
One of the first phylogenetic trees of the animal world, drawn by E. Haeckel (1866) under the influence of Charles Darwin's ideas. Relationships and the taxonomic rank of individual groups of organisms today we imagine differently (see, for example, Fig. XI-2, XI-3), but the images of the relationship of groups in the form of a tree remain today the only ones that reflect the history of the development of related groups of organisms.
Charles Darwin
On the Origin of Species by Natural Selection, or the Preservation of Favored Breeds in the Struggle for Life
Introduction
Traveling as a naturalist on Her Majesty's ship, the Beagle, I was struck by some of the facts about the distribution of organic beings in South America and the geological relations between former and modern inhabitants of this continent. These facts, as will be seen in later chapters of this book, seem to illuminate to some extent the origin of species—that mystery of mysteries, in the words of one of our greatest philosophers. On returning home, in 1837, I came to the idea that perhaps something could be done to settle this question by patiently collecting and pondering all sorts of facts that had anything to do with it. After five years of labour, I have allowed myself some general reflections on this subject, and have sketched them in the form of short notes; this sketch I expanded in 1844 into a general sketch of the conclusions which then seemed to me probable; from that time to the present day, I have stubbornly pursued this subject. I hope I will be forgiven for these purely personal details, as I cite them to show that I was not hasty in my conclusions.
My work is now (1858) almost finished; but as it will take me many more years to complete it, and my health is far from flourishing, I was persuaded to publish this summary. I was particularly moved to do this by the fact that Mr. Wallace, now a student of the natural history of the Malay Archipelago, came to almost exactly the same conclusions as I have reached on the origin of species. In 1858 he sent me an article on the subject with a request that it be forwarded to Sir Charles Lyell, who forwarded it to the Linnean Society; it is published in the third volume of the magazine of this Society. Sir C. Lyell and Dr. Hooker, who were aware of my work, the last to read my 1844 essay, did me the honor of advising me to publish, with Mr. Wallace's excellent paper, a brief excerpt from my manuscript.
The summary now published is necessarily imperfect. I cannot give here references or point to authorities in support of this or that proposition; I hope the reader will rely on my accuracy. No doubt errors have crept into my work, although I have constantly taken care to trust only good authorities. I can only state here the general conclusions I have arrived at, illustrating them with only a few facts; but I hope that in most cases they will be enough. No one more than I is aware of the need to present later in full detail the facts and references on which my conclusions are based, and I hope to do this in the future in my work. I am very well aware that there is almost not a single proposition in this book in relation to which it would not be possible to present facts leading, apparently, to conclusions directly opposite to mine. A satisfactory result can be obtained only after a full presentation and evaluation of the facts and arguments testifying for and against on each issue, and this, of course, is not possible here.
I am very sorry that lack of space deprives me of the pleasure of expressing my gratitude for the generous assistance rendered to me by many naturalists, partly even unknown to me personally. But I cannot, however, miss the opportunity to express how deeply I am indebted to Dr. Hooker, who over the past 15 years has helped me in every possible way with his vast knowledge and clear judgment.
Therefore, it is extremely important to have a clear understanding of the means of modification and co-adaptation. At the beginning of my research, it seemed likely to me that a careful study of domesticated animals and cultivated plants would provide the best opportunity to sort out this obscure problem. And I wasn't wrong; in this, as in all other perplexing cases, I have consistently found that our knowledge of variation in domestication, though incomplete, is always the best and surest clue. I may allow myself to express my conviction of the exceptional value of such studies, despite the fact that naturalists have usually neglected them.
On the basis of these considerations, I dedicate Chapter I of this brief Exposition of Variation in Domestication. We shall thus ascertain that hereditary modification on a large scale is at least possible, and we shall also learn, equally or more importantly, how great is man's capacity for cumulation by his Selection of successive slight variations. I will then move on to the variability of species in the state of nature; but, unfortunately, I shall be forced to deal with this question only in the most brief outline, since a proper presentation of it would require long lists of facts. We shall, however, be in a position to discuss what conditions are most favorable for variation. The next chapter will deal with the Struggle for Existence between all organic beings throughout the world, which inevitably results from the exponential growth of their numbers. This is the doctrine of Malthus, extended to both kingdoms - animals and plants. Since many more individuals of each species are born than can survive, and since, consequently, a struggle for existence often arises, it follows from this that any creature that, in the complex and often changing conditions of its life, although slightly varies in its advantageous direction, will be more likely to survive and thus be subject to natural selection. By virtue of the strict principle of heredity, the selected variety will tend to reproduce in its new and modified form.
This fundamental question of Natural Selection will be dealt with in detail in Chapter IV; and we shall see then how Natural Selection almost inevitably brings about the Extinction of many less perfect forms of life, and leads to what I have called the Divergence of Character. In the next chapter, I will discuss the complex and obscure laws of variation. In the next five chapters, the most obvious and most essential difficulties encountered by theory will be analyzed, namely: firstly, the difficulties of transitions, i.e., how a simple being or a simple organ can be transformed and improved into a highly developed being or into a complexly constructed organ; secondly, the question of Instinct, or the mental faculties of animals; thirdly, Hybridization, or sterility, when crossing species, and fertility when crossing varieties; fourthly, the incompleteness of the Geological Chronicle. In Chapter XI I shall consider the geological succession of organic beings in time; in XII and XIII - their geographical distribution in space; in XIV - their classification or mutual relationship both in the adult and in the embryonic state. In the last chapter I will present a brief recapitulation of what has been said throughout the work, and a few concluding remarks.
The history of the development and origin of the human species has been of concern to scientists and many ordinary people for centuries. At all times, all sorts of theories have been put forward on this score. These include, for example, creationism - the Christian philosophical and theistic concept of the origin of Everything from the creative act of God; the theory of external interference, according to which the Earth was inhabited by people due to the activities of extraterrestrial civilizations; the theory of spatial anomalies, where the fundamental creative force of the Universe is the humanoid triad "Matter - Energy - Aura"; and some others. However, the most popular and generally accepted theory of anthropogenesis, as well as the origin of species of living beings in general, is, of course, Charles Darwin's theory of the origin of species. Today we will look at the basic principles of this theory, as well as the history of its origin. But first, traditionally, a few words about Darwin himself.
Charles Darwin was an English naturalist and traveler who became one of the founders of the idea of the evolution in time of all living organisms from common ancestors. Darwin considered natural selection to be the main mechanism of evolution. In addition, the scientist was engaged in the development of the theory of sexual selection. One of the main studies of the origin of man also belongs to Charles Darwin.
So how did Darwin come up with his theory of the origin of species?
How did the origin of species theory come about?
Born into a physician's family, Charles Darwin, while studying at Cambridge and Edinburgh, developed a profound knowledge of geology, botany, and zoology, as well as the fieldwork skills he craved.
A huge influence on the formation of Darwin's worldview as a scientist was exerted by the work "Principles of Geology" by Charles Lyell, an English geologist. According to him, the modern appearance of our planet was gradually formed under the influence of the same natural forces that continue to act in our day. Charles Darwin was naturally familiar with the ideas of Jean Baptiste Lamarck, Erasmus Darwin, and several other early evolutionists, but none of them affected him as much as Liley's theory.
However, a truly fateful role in the fate of Darwin was played by his journey on the Beagle ship, which took place from 1832 to 1837. Darwin himself said that the following discoveries made the greatest impression on him:
- The discovery of fossil animals of gigantic size and covered with a shell, which was similar to the shell of armadillos familiar to all of us;
- The evidence that species of animals close in genus replace each other as they move along the South American mainland;
- The evidence that the species of animals on the various islands of the Galapagos archipelago differ only slightly from each other.
Subsequently, the scientist concluded that the above facts, like many others, can only be explained if we assume that each of the species underwent constant changes.
After Darwin returned from his travels, he began to ponder the problem of the origin of species. Many ideas were considered, including the idea of Lamarck, but all of them were discarded for lack of explanation for the amazing ability of plants and animals to adapt to environmental conditions. This fact, considered by the early evolutionists to be self-evident, became Darwin's most important question. So he began to collect information on the variability of plants and animals in natural and domestic conditions.
Many years later, recalling the emergence of his theory, Darwin wrote that very soon he realized that it was selection that had the main role in the successful creation of useful plant and animal species by man. Although, for some time the scientist still could not understand how selection can be applied to those organisms that live in the natural environment.
It was during this period that the ideas of Thomas Malthus, an English scientist and demographer, were actively discussed in the scientific circles of England, who said that the population of the population was growing exponentially. After reading his work On Population, Darwin continued his previous thought by saying that long-term observations of the way of life of plants and animals prepared him to appreciate the significance of the ubiquitous struggle for existence. But he was struck by the thought that favorable changes in such conditions should remain and be preserved, and unfavorable should be subjected to destruction. The result of this whole process should be the appearance of new species.
As a result, in 1838 Darwin came up with the theory of the origin of species through natural selection. However, the publication of this theory did not take place until 1859. And the reason for the publication was rather dramatic circumstances.
In 1858 a man named Alfred Wallace, a young British biologist, naturalist and traveller, sent Darwin the manuscript of his paper On the Tendency of Varieties to Deviate Unlimitedly from the Original Type. This article presented a presentation of the theory of the origin of species through natural selection. Darwin decided not to publish his work, but his associates Charles Lyell and Joseph Dalton Hooker, who had long known about the ideas of their friend and were familiar with the outlines of his work, were able to convince Darwin that the publication of the work should take place simultaneously with the publication of Wallace's work.
So, in 1959, Charles Darwin's work "The Origin of Species by Means of Natural Selection, or the Preservation of Favorable Races in the Struggle for Life" was published, and its success was simply stunning. Darwin's theory was well received and supported by some scientists and severely criticized by others. But all subsequent works of Darwin, like this one, immediately acquired the status of bestsellers after publication and were published in many languages. The scientist himself in the blink of an eye gained world fame.
And one of the reasons for the popularity of Darwin's theory was its basic principles.
The main principles of the theory of the origin of species by Charles Darwin
The whole essence of Darwin's theory of the origin of species lies in a set of provisions that are logical, capable of being verified experimentally and confirmed by facts. These provisions are as follows:
- Any kind of living organisms includes a huge range of individual genetic variability, which can differ in morphological, physiological, behavioral and any other features. This variability can be continuous quantitative or discontinuous qualitative, but exists at any time. It is impossible to find two individuals that would be absolutely identical in terms of the totality of features.
- Any living organism has the ability to rapidly increase its population. There can be no exception to the rule that organic beings multiply in such a progression that if they were not exterminated, then one pair could cover the entire planet with offspring.
- For any kind of animal, there are only limited resources for life. For this reason, a large production of individuals should serve as a catalyst for the struggle for existence either between members of the same species, or between members of different species, or with the conditions of existence. The struggle for existence, according to Darwin's theory, includes both the struggle of a representative of a species for life, and its struggle for the successful provision of its offspring.
- In the struggle for existence, only the most adapted individuals are able to survive and successfully produce offspring, which have special deviations that have turned out to be adaptive to specific environmental conditions. Moreover, such deviations occur precisely by chance, and not in response to the influence of the environment. And the usefulness of these deviations is also random. The deviance is passed on to the descendants of the individual that survives at the genetic level, causing them to become more adapted to their environment than other individuals of the same species.
- Natural selection is the process of survival and preferential reproduction of the fittest members of a population. Natural selection, according to Darwin, in the same way constantly fixes any changes, preserves the good and discards the bad, as does a breeder who studies many individuals and selects and breeds the best of them.
- With regard to individual isolated varieties in different living conditions, natural selection leads to a divergence of their characteristics and, as a result, to the formation of a new species.
These provisions, which are practically flawless in terms of
Charles Darwin
On the Origin of Species by Natural Selection, or the Preservation of Favored Breeds in the Struggle for Life
Introduction
Traveling as a naturalist on Her Majesty's ship, the Beagle, I was struck by some of the facts about the distribution of organic beings in South America and the geological relations between former and modern inhabitants of this continent. These facts, as will be seen in later chapters of this book, seem to illuminate to some extent the origin of species—that mystery of mysteries, in the words of one of our greatest philosophers. On returning home, in 1837, I came to the idea that perhaps something could be done to settle this question by patiently collecting and pondering all sorts of facts that had anything to do with it. After five years of labour, I have allowed myself some general reflections on this subject, and have sketched them in the form of short notes; this sketch I expanded in 1844 into a general sketch of the conclusions which then seemed to me probable; from that time to the present day, I have stubbornly pursued this subject. I hope I will be forgiven for these purely personal details, as I cite them to show that I was not hasty in my conclusions.
My work is now (1858) almost finished; but as it will take me many more years to complete it, and my health is far from flourishing, I was persuaded to publish this summary. I was particularly moved to do this by the fact that Mr. Wallace, now a student of the natural history of the Malay Archipelago, came to almost exactly the same conclusions as I have reached on the origin of species. In 1858 he sent me an article on the subject with a request that it be forwarded to Sir Charles Lyell, who forwarded it to the Linnean Society; it is published in the third volume of the magazine of this Society. Sir C. Lyell and Dr. Hooker, who were aware of my work, the last to read my 1844 essay, did me the honor of advising me to print, along with Mr. Wallace's excellent paper, brief excerpts from my manuscript.
The summary now published is necessarily imperfect. I cannot give here references or point to authorities in support of this or that proposition; I hope the reader will rely on my accuracy. No doubt errors have crept into my work, although I have constantly taken care to trust only good authorities. I can only state here the general conclusions I have arrived at, illustrating them with only a few facts; but I hope that in most cases they will be enough. No one more than I is aware of the need to present later in full detail the facts and references on which my conclusions are based, and I hope to do this in the future in my work. I am very well aware that there is almost not a single proposition in this book in relation to which it would not be possible to present facts leading, apparently, to conclusions directly opposite to mine. A satisfactory result can be obtained only after a full presentation and evaluation of the facts and arguments testifying for and against on each issue, and this, of course, is not possible here.
I am very sorry that lack of space deprives me of the pleasure of expressing my gratitude for the generous assistance rendered to me by many naturalists, partly even unknown to me personally. But I cannot, however, miss the opportunity to express how deeply I am indebted to Dr. Hooker, who over the past 15 years has helped me in every possible way with his vast knowledge and clear judgment.
Therefore, it is extremely important to have a clear understanding of the means of modification and co-adaptation. At the beginning of my research, it seemed likely to me that a careful study of domesticated animals and cultivated plants would provide the best opportunity to sort out this obscure problem. And I wasn't wrong; in this, as in all other perplexing cases, I have consistently found that our knowledge of variation in domestication, though incomplete, is always the best and surest clue. I may allow myself to express my conviction of the exceptional value of such studies, despite the fact that naturalists have usually neglected them.
On the basis of these considerations, I dedicate Chapter I of this brief Exposition of Variation in Domestication. We shall thus ascertain that hereditary modification on a large scale is at least possible, and we shall also learn, equally or more importantly, how great is man's capacity for cumulation by his Selection of successive slight variations. I will then move on to the variability of species in the state of nature; but, unfortunately, I shall be forced to deal with this question only in the most brief outline, since a proper presentation of it would require long lists of facts. We shall, however, be in a position to discuss what conditions are most favorable for variation. The next chapter will deal with the Struggle for Existence between all organic beings throughout the world, which inevitably results from the exponential growth of their numbers. This is the doctrine of Malthus, extended to both the animal and vegetable kingdoms. Since many more individuals of each species are born than can survive, and since, consequently, a struggle for existence often arises, it follows from this that any creature that, in the complex and often changing conditions of its life, although slightly varies in its advantageous direction, will be more likely to survive and thus be subject to natural selection. By virtue of the strict principle of heredity, the selected variety will tend to reproduce in its new and modified form.
This fundamental question of Natural Selection will be dealt with in detail in Chapter IV; and we shall see then how Natural Selection almost inevitably brings about the Extinction of many less perfect forms of life, and leads to what I have called the Divergence of Character. In the next chapter, I will discuss the complex and obscure laws of variation. In the next five chapters, the most obvious and most essential difficulties encountered by theory will be analyzed, namely: firstly, the difficulties of transitions, i.e., how a simple being or a simple organ can be transformed and improved into a highly developed being or into a complexly constructed organ; secondly, the question of Instinct, or the mental faculties of animals; thirdly, Hybridization, or sterility, when crossing species, and fertility when crossing varieties; fourthly, the incompleteness of the Geological Chronicle. In Chapter XI I shall consider the geological succession of organic beings in time; in XII and XIII - their geographical distribution in space; in XIV - their classification or mutual relationship both in the adult and in the embryonic state. In the last chapter I will present a brief recapitulation of what has been said throughout the work, and a few concluding remarks.
No one will be surprised that much remains unexplained in the question of the origin of species and varieties, if only we are aware of our deep ignorance of the mutual relations of the multitude of beings around us. Who can explain why one species is widespread and numerous, and another species close to it has a narrow area of distribution and is rare. And yet these relations are of the utmost importance, for they determine the present welfare and, I believe, the future success and modification of every inhabitant of the earth. We know even less about the mutual relations of the innumerable inhabitants of our planet during the past geological epochs of its history. Although much is still incomprehensible and will remain incomprehensible for a long time, I have no doubt, after the most careful study and impartial discussion that I am capable of, that the view, until recently shared by the majority of naturalists, and previously shared by me, namely, that each species was created independently of the others - erroneously. I am quite convinced that species are not immutable, and that all species belonging to what we call the same genus are direct descendants of one of some, for the most part, extinct species, just like the recognized varieties of one of some species are descendants of that species. Moreover, I am convinced that Natural Selection was the most important, but not the only means of modification.
