Charles Darwin The origin of species by natural selection. Charles Darwin The Origin of Species by Natural Selection, or the Preservation of Favorable Races in the Struggle for Life

If, under the changing conditions of life, organic beings discover individual differences in almost any part of their organization, and this cannot be disputed; if in force geometric progression 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 recall the infinite complexity of the relationships of organisms, both among themselves and to their living conditions, and the infinite variety arising from these relationships useful features structure, constitution, and habits—when all these things are taken into account, it would be extremely improbable that changes beneficial to the organism possessing them would never appear, just as numerous changes beneficial to man did. 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 can be considered an ascent to a higher level of organization. Yet 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 useful exclusively 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 one can easily explain both the nature of affinity and the usual presence of well-marked boundaries between innumerable organic beings of every class throughout the world. 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; the species of different genera are even less closely related to each other, and, finally, the genera representing various degrees 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 due to heredity and complex action natural selection, resulting in 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. Green branches with blossoming buds represent existing species, and the branches of 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 overcome other species in great fight for a 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, which to some extent unites two great branches of life by their affinity and has escaped 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 power of reproduction 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, crocodile and frog, in the highest degree similar: it is convenient for observing over 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 traits 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 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 different classes(1) such as birds - reptiles (lizard, turtles), fish and amphibians (5-15% homology). From 15 to 45% homology in DNA in representatives different units within the same class (2), 50-75% among 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 taxonomic rank individual groups Today we imagine organisms in a different way (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 development related groups 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 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, 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 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 then see how Natural Selection almost inevitably brings about the Extinction of many less perfect forms life and leads to what I have called Sign Divergence. 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.

Origin of Species by Natural Selection, or Conservation favorable races in the fight for life
On the Origin of Species
Front page 1859 editions On the Origin of Species
Author	Charles Darwin
Genre	science, biology
Original language	English
Original published	November 24
Publisher	John Murray
Release	November 24
Pages	502
Carrier	Print (Hardback)
ISBN
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In that scientific work Darwin presents a long chain of arguments in favor of his theory. According to it, groups of organisms (today called populations) gradually develop due to natural selection. Exactly at this work this process was first introduced to the general public. Subsequently, the set of principles outlined by Darwin came to be called Darwinism. In particular, Darwin showed detailed scientific evidence collected during his voyage to South America, the Galapagos Islands, and Australia aboard the Beagle from 1831 to 1836. At the same time, he refuted the doctrine of "created species" (eng. created kinds), on which the entire biology of his era was based.

Various evolutionary ideas have already been proposed to explain new discoveries in biology. Thus, there was growing support for such ideas among dissident anatomists and the general public, but in the first half of the 19th century, English scientific institution was closely associated with the English Church, while science was part of natural theology. The notions of species transmutation were controversial because they conflicted with the belief that species were fixed parts of a design hierarchy and that humans were unique and not related to other animals.

The book was understandable to a wide readership and caused great interest already at publication. The first print run of 1,250 copies was sold out on the same day. The theses presented in it are still the basis of the scientific theory of evolution.

The history of the development of evolutionary doctrine

Prerequisites

At least in later editions, Darwin noted the presence of rudiments evolutionary doctrine among ancient thinkers, in particular Aristotle. Georges Buffon already suggested in 1766 that similar animals such as the horse and donkey, or the tiger and leopard, are species that share a common ancestor.

The origin of evolutionary doctrine

In 1825 Darwin entered Faculty of Medicine University of Edinburgh. Soon, in his second year, he became interested in natural history and gave up his medical studies to study marine invertebrates with Robert Grant. The latter was a proponent of Lamarck's theory of the rebirth of species. In 1828, at the urging of his father, Darwin entered Christ's College, Cambridge University, to be ordained a priest in the Church of England. While studying theology, philosophy, the classics of literature, mathematics and physics, he especially delved into botany and entomology.

In December 1831, after graduating and becoming 10th in a list of 178 who successfully passed the exam, Darwin set sail on the Beagle as a naturalist. By that time, he was familiar with the writings of Lyell and during the journey he became convinced of the validity of the theory of uniformitarianism. The first landing on Santiago Island reinforced his belief that uniformitarianism was the key to understanding the history of the landscape.

History of the writing and publication of The Origin of Species

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 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.

The work "Principles of Geology" by Charles Lyell, an English geologist, had a huge influence on the formation of Darwin's worldview as a scientist. 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 was growing exponentially. 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 omnipresent 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'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 experimentally verified 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 adapted 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 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 be impossible 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.