Darwin's theory of the origin of species. Charles Darwin - Origin of Species by Natural Selection, or the Preservation of Favorable Races in the Struggle for Life

The theory of evolution in the middle of the last century produced the same effect as the theory of Copernicus in its time. It was scientific revolution and not only in the field of biology. Evolutionism has changed the image of man. If the Copernican revolution changed the idea of the spatial order in the Universe, indicating to man a different place than before, then Darwin revised the temporal order. The place and role of man in nature were radically revised by the efforts of Copernicus and Darwin.

Charles Darwin (1809-1882) at first tried himself in the field of medicine, a church career, until in 1831 he was on board the English ship Beagle, bound for circumnavigation, as a naturalist. The travelers departed Devon Port on December 27, 1831, and returned to Falmouth on October 2, 1836. In 1839, Darwin published travel diaries in "A naturalist's journey around the world". During this more than important scientific journey, Darwin studied "Fundamentals of Geology" Charles Lyell (1797-1875). The history of the earth was explained by Lyell as the action of forces that changed earth's surface(floods, volcanic eruptions, rainstorms, landslides, etc.), by the same laws that

Darwin: On the Origin of Species 233

explain the facts of the present. So there were doubts about the biblical version of the origin of the earth and living beings.

in the Galapagos Islands (an archipelago in pacific ocean) Darwin discovered a group of finches that had, depending on the habitat, beaks of different proportions. It was obvious that species characteristics were capable of changing gradually, just as it was also obvious that all the endless cases of adaptation (woodpecker, tree frog, etc.) are difficult to explain only by environmental conditions. Upon returning to England, Darwin collects information about different types animals and plants both in nature and at home, consults with gardeners and pastoralists and carefully records the data obtained.

A lot of time passed before the scientist came to the conclusion that it was with the help of selection that a person learned to grow the necessary and useful species of plants and animals. It remains to be seen how the selection takes place in natural environment. Starting systematic research in October 1838, Darwin read Malthus' writings on population in his spare time. Understanding well the significance of the factor of the struggle for existence, no matter what kind of form was discussed, he was suddenly struck by the conjecture that under the influence of changing circumstances, most likely, favorable and corresponding changes are preserved, and inappropriate forms are destroyed. So the idea was born new theory, says the scientist in his Autobiography. It took more than twenty years to develop it.

In 1857, the first publication appeared outlining evolutionary theory in the Journal of the Meetings of the Linnean Society. A b 1859 book by Darwin "The Origin of Species by natural selection» saw the light. It said that the environment produces a selection of the most acceptable hereditary changes. Selection, in other words, is expressed in evolutionary orientation, because it determines the adaptation of organisms to the environment. Evolution can be interpreted as a series of adaptations, each of which certain kind fixes or loses under the pressure of selection for a long time.

The success of the book is evidenced by the fact that 1250 copies of the first edition were sold on the first day, as well as 3000 copies of the second edition that soon appeared. What is the theoretical novelty of the book, which had such an unprecedented success?

Darwin identified five types of evidence for evolutionary theory. 1. Evidence regarding heredity and cultivation, considering the changes brought about by domestication.

2. Evidence related to geographical distribution.

3. Archaeologically obtained evidence. 4. Evidence related to the mutual similarity of living beings. 5. Evidence obtained from embryology and from the study of vestigial organs.

234 Development of the sciences in the 19th century

AT "The Origin of Species" we read: many are convinced that “each species was created one independently of the other. But my way of thinking is more consistent with what is known from the laws imprinted in matter by the Creator: the appearance and distribution of the past and present inhabitants of the world is due to secondary causes similar to those that determine the birth and death of an individual. When I consider living beings not as special creations, but rather as direct descendants of a few beings who lived long ago, in the first centuries of the Silurian period, they appear to me ennobled.

The laws "imprinted in matter", according to Darwin, are quite simple: development through reproduction; variability associated with direct and indirect effects of living conditions, use and non-use of organs; an increase in numbers and, as a result, an intensification of the struggle for existence; divergence of characteristics and prevalence of less perfect forms. Consequently, in the process of natural struggle, something beyond all expectations is born - the formation of developed animals. This is a grandiose conception of life - from initially one or a few forms to more and more complex. "Rotating according to its immutable laws of gravity, the planet evolves, starting from simple ones, to come to infinitely beautiful and amazing forms."

Charles Darwin's book "The Origin of Species" became his main work, telling the world about the evolutionary theory of the development of life on Earth. Its influence on all science was colossal. With his publication, the British scientist laid the foundation for new era in biology.

The history of the appearance of the book

The Origin of Species was published by Darwin in 1859. The appearance of the book was preceded by many years of work of the researcher. The work was based on the notes that Darwin had kept since 1837. As a naturalist, he visited world tour on the Beagle. Observations of the fauna of South America and tropical islands during this voyage made the British think about whether the church theory about the divine

Darwin's predecessor was Charles Lyell. His ideas also inspired the traveler. Finally, after two decades of hard work, On the Origin of Species was born. The main message of the author was this: all types of plants and animals change over time. The main stimulus for these metamorphoses is the struggle for life. From generation to generation, a species acquires useful traits and gets rid of superfluous ones in order to adapt to existence in a changing environment.

Selection and evolution

Darwin's publication had the effect of an exploding bomb. On the Origin of Species sold out great speed, and the more rumors spread about this book, the greater the demand. Within two or three years, translations into the main European languages appeared.

What surprised the progressive public so much? In the introduction to the book, Darwin summarized his main ideas. Further, the author gradually carefully argued each of his thesis. First, he considered the experience of horse breeding and breeding pigeons. The experience of breeders has become another source of inspiration for the scientist. He posed the question to readers: "Why do domestic animal breeds change and differ from their wild relatives?" With this example, Darwin briefly explained the origin of species on a larger, worldwide scale. Like domestic populations, they all gradually transformed due to environmental changes. But if in cattle breeding there is something undertaken by man, then in nature there is

Genus and species

In the era of Darwin, there was still no single and generally accepted species system. Scientists have suggested various theories and hypotheses of grouping living beings. The same attempt was made in the book On the Origin of Species. Charles Darwin proposed a gender classification. Each such unit includes several types. This principle is universal. For example, there are many types of horses. Some of them are larger, some are faster, some are found only in a certain region. Thus, species are only varieties of one common genus.

The palette of individual differences arose thanks to nature. The order established in it is a constant. In the course of it, the species change and are divided into subspecies, which, over time, are more and more different from each other. The smallest unique feature (for example, the shape of a bird's beak) can become a significant advantage in survival. An individual that manages to survive, unlike dissimilar neighbors, will pass on its characteristics by inheritance to offspring. And after a few generations, a unique feature will become feature already many individuals.

Controversy with opponents

In the 6th and 7th chapters of his book, Charles Darwin responds to the criticism of the opponents of his theory. In the first publication, he rather intuitively guessed the claims of creationists, church officials and other scientists. In subsequent lifetime reprints, the author answered the objections of specific opponents, naming them by name.

It is known that Charles Darwin was not an eloquent orator in public. In the stands, his theory was best defended by Thomas Huxley. But in the silence of the office, Darwin formulated everything succinctly and accurately. He smashed his opponents one by one, which only drew more attention to the book.

paleontological notes

It was not without reason that the British scientist wrote The Origin of Species for so long. Charles Darwin not only explained his theory in terms of biology, but also argued with the help of geographical distribution and paleontology. The scientist drew attention to the numerous finds of fossils that recorded traces of extinct life forms. Thanks to paleontology, it became possible to study extinct and intermediate species in detail.

It was the works of Darwin that made this science extremely popular, which is why it experienced a real flowering in the second half of the 19th century. The scientist was one of the first to describe the mechanism for preserving the remains. He noted that in normal conditions environment organic tissues die off and leave no traces. However, when they get into water, permafrost or amber, they remain for a long time.

Species distribution

Arguing about the migration and relocation of species, Darwin was able to build an organic system from the chaos of notes and facts, full of rules and patterns. The results of natural selection can cover entire climatic zones. The biologist, however, noted that there are natural barriers to the spread of animals and plants. At land species such an insurmountable barrier - huge bodies of water between the New and Old Worlds.

Interestingly, in his reasoning, Darwin dismissed theories about the disappeared continents (for example, about Atlantis). Curious are his arguments about how plants spread from mainland to mainland. The scientist put forward a hypothesis that can be explained by the following example. The seeds can be swallowed by birds, which, when flying to the other side of the world, leave them there in excrement. This conclusion was not the only one. Seedlings could stick to the paws of birds along with the mud and, together with them, fall on new mainland. Further spread plants became a matter of time.

Embryo features

In Chapter 14, Darwin drew attention to the similarity of vestigial organs and embryonic development in plants and animals. From this observation, he concluded that the origin of all species is common. On the other hand, the scientist explained the similarity of some signs by the same habitat. For example, fish and whales actually have little in common, although outwardly they look approximately the same.

Darwin also emphasized that larvae of the same species, when they enter different conditions will behave completely differently. All the instincts of the embryos are connected with only one factor - the desire to survive in a changing environment. Speaking about the larvae, the scientist called them a kind of chronicle of the whole species to which they belong.

End of book

At the end of his work, Darwin summarized his own discoveries. His book was typical Victorian England with all the diplomacy and roundness of wording customary for that time. For example, although the author became the founder scientific explanation shaping life, he made several conciliatory gestures towards religion.

The results of natural selection and the theory of evolution immediately became a serious problem for the church. In the epilogue, Darwin recalled that Leibniz once criticized physical laws Newton, but time has shown that these attacks were erroneous. The author of the sensational work expressed the hope that his own book will also find recognition, despite the serious pressure of creationists and other skeptics. Today we can say with certainty that this is exactly what happened.

History of development and origin human species for centuries, scientists and many ordinary people. 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; theory of external intervention, according to which the Earth was inhabited by people through the activities extraterrestrial civilizations; theory of spatial anomalies, where the fundamental creative force The Universe is a 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 to a physician's family, Charles Darwin, while studying at Cambridge and Edinburgh, developed a deep 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, modern look of our planet was gradually shaped by the same natural forces that continue to act today. Charles Darwin was naturally familiar with the ideas of Jean Baptiste Lamarck, Erasmus Darwin and some other evolutionists. early period, but none of them worked for him like Liley's theory did.

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, which the early evolutionists considered unsubstantiated, became for Darwin the most important issue. 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 the main importance in the successful creation of beneficial species plants and animals had precisely the selection. 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 is growing in geometric progression. After reading his On Population, Darwin continued his earlier thought by saying that long-term observations of the way of life of plants and animals had 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 is a young British biologist, a naturalist and traveler, sent Darwin the manuscript of his article "On the tendency of varieties to deviate indefinitely 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 published his work “The Origin of Species by Means of Natural Selection, or the Conservation of favorable races in the struggle for life, ”and her 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 intermittent qualitative character, 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, 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 various kinds, or with 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 deviation is passed on to the descendants of the individual that survives at the genetic level, causing them to become more adapted to the 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 various conditions life, 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 HMS Beagle, I was struck by some of the facts about the distribution of organic beings in South America and geological relationships between former and modern inhabitants of this continent. These facts, as will be seen in later chapters of this book, seem to shed some light on the origin of species—that mystery of mysteries, in the words of one of our the 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 labor I have allowed myself some general reflections on this subject, and have sketched them in the form brief 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 especially moved to do this by what Mr. Wallace, now studying natural history of the Malay Archipelago, came to almost exactly the same conclusions that I have reached on the question of 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 knew of my work, - the last to read my essay of 1844 - did me the honor of advising me to print, along with Mr. Wallace's excellent article, and 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 be impossible to present facts leading, apparently, to conclusions directly opposite to mine. Satisfactory results can only be obtained after complete presentation and an assessment of the facts and arguments that testify 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, in the highest degree it is important to have a clear understanding of the means of modification and co-adaptation. At the beginning of my research, it seemed to me likely that a careful study of domesticated animals and cultivated plants would present best opportunity deal with 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. Then I will move on to species variability in natural state; but, unfortunately, I will be forced to touch on this issue only in the most brief outline, since its proper presentation would require long lists of facts. We shall, however, be in a position to discuss what conditions are most favorable for variation. AT next chapter the Struggle for Existence between all organic beings throughout the world will be considered, which inevitably follows from the geometric progression of their growth in 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 dealt with, namely: first, 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; second, the question of Instinct, or mental abilities 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. AT last chapter I will present a brief recapitulation of what has been said throughout the work, and a few concluding remarks.

Charles Robert Darwin

The Origin of Species by Natural Selection, or the Preservation of Favorable Races in the Struggle for Life

Charles Robert Darwin (1809–1882)

Original Edition:

Charles Robert Darwin

On the Origin of Species by Means of Natural Selection,

or the Preservation of Favored Races in the Struggle for Life

Translation from the sixth edition (London, 1872)

academicians K.A. Timiryazev, M.A. Menzbir, A.P. Pavlov and I.A. Petrovsky

Introduction

Traveling as a naturalist on Her Majesty's ship, the Beagle, I was struck by certain 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 knew of my work, the last to read my 1844 essay, did me the honor of advising me to publish, with Mr. Wallace's excellent article, 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.

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 summary change under the influence of 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 follows from the geometric progression of their growth in 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 dealt with, namely: first, 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 record. 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.