Darwinism and the problems of life : a study of familiar animal life

Preface

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The present work had its origin in an attempt to appreciate the range, the foundation, and the value of evolutionary theories. Such a task entailed a prolonged study, not only of scientific literature, but also of works that belong to neighbouring provinces.

The information gleaned from these fields had then to be appraised and put together, and an effort made to reduce it into a harmonious system. In doing

this the various theories had to be examined with discrimination, enlarged, and built into the structure. It is, therefore, hoped that the reader will meet many new thoughts in the work.

In the preparatory reading the author had to go through the whole of the relevant literature in various languages. In the book itself he was compelled to restrict himself to what had an essential bearing — either for or against — on the view it presents.

The work has not been written solely for those who are entirely devoted to the study of science. It appeals to all who take an interest in scientific questions ; to all educated people who would inform

PREFACE themselves as to the actual condition of theories of life.

Its chief aim has been to vindicate the value and importance of Darwinism. The greater part of the work is devoted to proving the truth of this system. On the other hand, every care has been taken to distinguish between facts and probabilities ; and it has been clearly pointed out what general deductions may or may not be drawn from Darwinism. The ease with which the theory of evolution is grasped too readily disposes people to regard Darwinism as the one true, natural, and sound view of the worldprocess. And in order to set forth all these questions with perfect clearness, it has been necessary to touch on fields of inquiry which lie beyond the range of biological science.

The manner of presentation is simple, because the work is written for the general reader. No knowledge of science is presupposed ; and the reader is briefly informed on all the questions that have a bearing on the theory of evolution. Everything that would interfere with clearness and intelligibility has been avoided. Hence, the founders of the various theories treated are not, as a rule, named in the text ; though, to ensure accuracy, their names are given in footnotes. In these notes will also be found the references to the literature relating to the subject, so

PREFACE that the reader who desires to go further into the matter will find every assistance. With the same object of making the text clear the various animals have been indicated, as far as possible, by their popular names, but their scientific titles will be found in the index at the end of the work.

The difficulty of many of the questions treated imposed a yet further condition. Problems that are not easily grappled could not very well be put at once before the reader. The book gradually educates him up to the level of these. Starting from familiar objects, it leads him on, almost unconsciously, to problems of increasing difficulty, until he is at length in a position to form an opinion on even the most difficult.

And as it is the purpose of this work to elucidate the theory of evolution only by means of observation, to convince those only who have some insight into the inexhaustible facts of nature that bear witness to it, as many as possible of these facts have been introduced. Nature herself shall teach the reader the truth of evolution. On this account, the first part of the work has been divided, not into problems, but according to groups of animals. These animals, moreover, are generally the familiar ones of our own country. Our indigenous animal-life has been treated very fully. Plants have only been dealt with in so

PREFACE far as this was necessary for the reader to understand the questions.

The book will, therefore, make the reader acquainted with the animals that surround him, and teach him to take an intelligent interest in the life of the forest and the field. In this we have the most natural foundation for the thoughts that reach out to embrace the whole of life, and that in the end help to lay open the entire world to the human mind.

CONRAD GUENTHER.

Preface To The Third Edition

Little over half a year has passed since the

publication of this work. In so short a space of

time there could not be much advance made in

science, so that it was unnecessary to make extensive

alterations in the text for the present edition. In a

few places there have been additions, relating to new

investigations ; the third chapter, especially, has been

considerably modified. No change was needed as

regards the view that runs through the entire work,

and is summarily presented in the final chapter. I

have carefully examined the objections raised on

several points, but have found them invalid. However,

I thought it proper to put the chief of them before

the reader, because I am anxious that he should use

his own judgment on the facts independently. I have,

therefore, given the objections in the notes, with a

few explanatory remarks. Where the objections were

due to misunderstanding, I have taken care to make

the corresponding passage in the text clearer, or to

add further explanations. The purely philosophical

questions that are dealt with in the later chapters have

not been enlarged on. A more thorough discussion of io PREFACE TO THIRD EDITION

these questions would spoil the unity of the work ; it was necessary only to put, at the limits of my science, sign-posts indicating the destination of the roads that start from these points, and distinguishing the right from the wrong way. For the rest, I believe that my treatment of these various questions is not wholly superficial, but sufficiently informs the reader on the substance of them. I am confirmed in this by the testimony of experts.

I have to express my cordial thanks to my colleagues for their friendly interest.

CONRAD GUENTHER.

Freiburg, 15 th March , 1905.

TRANSLATOR’S PREFACE

The quantity of popular evolutionary literature in our tongue is — apart from works that deal with the subject in its relation to religious controversy — so slight that a fresh work of acknowledged competence should be assured of a welcome. Professor Guenther’s work has, however, an especial title to consideration. He has succeeded so well in taking up the position of the average untrained observer for his instructive survey of our animal world that his book will be singularly helpful to thousands who shrink from the usual technical manual. The reader will find himself at first looking out on a familiar world in a familiar way. Gradually he will find the well - known forms and movements suggesting alluring problems to his opening vision, and he will follow the answers to them, given with a logical ease and literary grace that are too uncommon in this department, almost without effort.

Dr. Guenther’s facility has not been purchased, as often happens, at the expense of soundness or thoroughness. The limits of the work restrict his plan, but within those limits the reader will feel that he is following a judicious and entirely informed guide. Though full reference is made to the most recent speculations of biologists, it is not books and authorities, but Nature, that the author holds steadily in view, and his personal contributions to its interpretation will command respect.

1 2 translator’s preface

The circumstance that the work proceeds on a totally different principle of interpretation than others that I have recently introduced to English readers gave me a certain gratification. It is important to make clear that the superb procession of organic forms across the stage of our planet, which we sum up in the phrase, “ the evolution of life,” may be presented either in the terms of the older Darwinian theories or of the new ones associated with the great name of Weismann. The fact of evolution now stands solid and towering above all the clash of theories. Even the machinery of natural selection continues its vast work — if it does not increase it — whether or no we accept the transmission of acquired characteristics. It has seemed most expedient to put before the general reader a simple and untechnical interpretation of evolution from the Weismannic point of view (within limits) ; and it would be difficult to find a more suitable and attractive one than Professor Guenther’s Darwinism.

JOSEPH McCABE.

London, October , 1905.

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CHAPTER I. — Introduction

Animal-life in the forest, the field, and the pond. Variations of animals in different regions. Connection of animals in the same region. Over-production in nature. The relation of increase to the danger of destruction. The struggle for life. Artificial selection. Natural selection. Transformation of species. Different animals of former days as the parents of actual organisms. The theory of evolution.

Its predictions. Variation and heredity. Useful and harmful animals. Modification of our animal -world through civilisation - - - - - 19

CHAPTER II. — Mammals

Life of mammals. Protective value of colour. Origin of colour. Hibernation. Store-rooms. Increased production or diminished peril of destruction. Why mammals do not multiply more. The play of animals. Explanation of play by rest and the accumulation of energy. Human play. Imitation in play. Explanation of instinct. Instinct and intelligence. Exercise of the mind in the games of children. Pleasure in play. Conscious self-deception, imagination. Play and art. The animal is at the threshold of art. Sense of freedom in play. Games of children. Attention. The use of curiosity. The mind of the animal and of man - - - - - 52

CHAPTER III.— Birds

Sexual selection. Choice of females. Rejection of the hypothesis. Advance of the male’s senses. Selection of the strongest suitor. Explanation of coyness and the animal coquette. Female selection inadmissible. The love -dance. Selection of the apparent strongest. Colours as means of distinguishing species. Use of sounds. Pairing-calls. Origin and forms of song. Instrumental music of the birds. Migration. Speed of flight. Do birds tire ? The adaptations of the bird-body. Height of the migration-flight. Origin of migratory birds. Their strength, their power of presentiment. Routes of migrating birds. Their memory and sense of direction. Travelling in flocks ....

CHAPTER IV. — Reptiles and Amphibia

Principle of animal-classification. The general properties of animals explained by heredity and adaptation. Darwinian justification of classification. Reptiles and amphibia of former ages. Earlier periods of the earth. How and why the earth has changed up to the present. How the remains of earlier animals have been preserved. Gaps in the remains of extinct animals. Primitive man. Conflicts of extinct animals. Why the gigantic forms of earlier ages became extinct. The death of species. Transformation of species. Why ancient species have been preserved. Why there are still animals of the simplest type. Predominance of a species of animal. Predominance of man. Any variation is possible. Origin of flying animals. Life of our reptiles. Prey. The creeping of serpents. Regeneration, the power to re-form lost members. Its origin by natural selection. Frog-spawn. The skin of amphibia. Repellent and warning colours on nauseous and poisonous animals -

CHAPTER V.— Fishes

Origin of terrestrial vertebrates and of lungs. Similarities in the structure of animals. Transformation of organs. Creation or evolution? Many animals are worse than others in this. Selection only creates what is necessary. Atrophy of useless organs. Rudimentary organs in man. Degeneration of organs by panmixis. Indifferent characteristics of animals. The differences between species are adaptations. Correlation. Animals that are beyond the range of selection, Qualities and quantities. Explanation of atrophied organs by economy of sustenance and negative selection. Impossible to explain many rudimentary organs. The biogenetic law. Gills in the human embryo. Predatory fishes. The rhodeus and the pond-muscle. Senses of fishes, their dangers. History of the eel and the salmon. Artificial selection of fishes

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CHAPTER VI. — Tracheates

To the tracheates belong spiders and insects. How insects grow. Explanation of the metamorphoses of insects. Protective colouring on the wings of butterflies. The Lamarckian principle refuted by protective colours.

Insects that resemble objects. Mimicry. Exhalation from male butterflies. Sexual selection. Origin of

flowers due to insects. Parts of the insect’s mouth.

Refutation of the Lamarckian principle. The coat of insects cannot have arisen by use. Harmonious adaptations, co-adaptations. Co-adaptations that Lamarck cannot explain. Explanation of co-adaptations. Are instincts inherited habits? Instincts that can never be affected by the will. Spider’s webs. Care of the young. Instincts that are only used once. Are mutilations inherited ? Protective marks, mildew marks, foresight. Infection of embryo. Structure of the embryo. The inheritance of acquired characters is difficult to conceive. Untenability of the Lamarckian principle - - - - 184

CHAPTER VII. — Crabs and Molluscs

Economy of nature. The chemical constituents of bodies. Chemical combinations. The elements. The albuminoids. Biogens as constituents of living matter. Vital phenomena and apparent death. Metabolism. Structure of the living substance. Plants the foundation of life. Order of sustenance in nature. Flesh-eating is more natural to the animal than plant-diet. Are all variations useful to animals? Value of selection. Origin of the shells of snails. Change of functions. Development of the crab.

Why the embryonic development of an animal reproduces its racial history. Reconstruction of embryogenesis. Uncertainty of the biogenetic law. Parthenogenesis, the development of unfertilised eggs. Significance of the germ - cells. Significance of sexual reproduction. Amphimixis. Plural variations - - - - 228

CHAPTER VIII. — Worms and Ccelenterata

Genealogical tree of the animals. Descent of animals. Descent of man. Preservation of intermediate forms. The earthworm. Regeneration. Leeches. Parasitism. Origin of i6 rAGB

parasites from free animals. Organic changes in parasites.

How parasites are conveyed. Exchange of hosts. Life of the chief parasites : Trichinae, maw-worms, dochmius, tape-worms, etc. Danger of fins. Development of the liver-distoma. Friendships of animals. Symbioses - 262

CHAPTER IX.— Protozoa

The animal built up of cells. Principle of division of labour.

The greater the division of labour, the higher the animal’s organisation. Multicellular and unicellular animals. The protozoa, their form and reproduction. Structure of an animal in its development from the ovum onwards from rudimentary parts. Origin of the germ-cells. Outlines of a theory of heredity. Amphimixis of the protozoa.

Origin of sexual reproduction. Formation of seed and ova. Continuity of the germ-cells. Are any animals immortal? Death is not common to all animals. Origin of death. Permanent and temporary life. Has life come from the stars? Origin of life on the earth, spontaneous generation. How it is to be conceived. The first development of living matter. Formation and significance of the cell - nucleus. Significance of the fundamental parts. Relation of the rudimentary parts in amphimixis. When life is extinguished ------ 288

CHAPTER X. — Extensions of the Principle of Selection and other Involuntary Theories

Why there are numerous species to-day. Isolation facilitates the divergence of species. Modification of isolated animals. Movement and alteration of animals. Are species formed by isolation even without the aid of natural selection ? Definite variations. Germinal selection. Changes in the nutrition of the embryo are the foundation of variations.

Do useless organs disappear through germinal selection ? Refutation of germinal selection. Effect of external influences as modifying principle. Orthogenesis. Rejection of same. The mutation-theory. Variations and mutations.

Do variations proceed indefinitely ? Is there a formative energy in organisms ? Mechanicism and vitalism. How are the form and purposiveness of organisms explained?

What is to be understood by chance. Absence of purpose in living things. The will to live, the instinct of self-preservation 324 spicuous shade of colour, otherwise the animals would show themselves against the grey soil, and would be more easily found and captured.

All these characteristics of the hare are continually improved by natural selection, as only those can escape their enemies that are best qualified to do so. But as their enemies also are subjected to an improving selection, higher qualifications will be required in the next generation, and so on. In other words, the hares will advance in each generation. It is true that we do not directly observe this progress, but that is only because our life is too short to appreciate the changes brought about by natural selection, which require long periods of time. Natural selection cannot act with the same intensity as artificial selection. In the case of the hare, for instance, not only two or three of the swiftest survive, but a large number, and amongst these many slow ones that have managed to escape destruction by a favourable accident. It is only on the average that the speediest survive, and, in fact, when we take an average of many years, so that it will be thousands of years before any appreciable result can be seen. We do not see the grass growing, but we can prove that it is longer to-day than it was yesterday. So, if we could raise from the dead a man who had seen a hare thousands of years ago, he would find a difference in the hare of to-day. In point of fact, the skeletons of animals belonging to earlier ages prove that they were different then from what they are in our time.

But we should greatly underrate the power of natural selection if we attributed to it only the capacity to

c increase already existing characteristics. Just as artificial selection can produce white pigeons from birds of a grey-blue colour, by choosing in each generation the specimens with the largest number of white spots in their plumage, so natural selection can endow animals with entirely new features. Thus, for instance, our hare is not easy to distinguish from the ground on which it browses because of its grey colour — which is a mixture of brown, yellow, white, and black.1 Now let us suppose that a glacial period came over England again, as has happened twice in the history of the earth. The dark-coloured hares would then easily meet the eyes of their enemies on the white snow, but there would be varieties with a rather stronger mixture of white in their colouring. These would be least easily seen, would survive the longest, and bring most young into the world ; so that the next generation would in itself be of a lighter shade. Amongst these, again, the lightest would survive best, and this would be repeated in each generation until a pure white coat was produced, as is found in the Arctic hare. We must not forget, of course, that such a modification of colour could only take place if the cold set in gradually, and implied above all the coming of longer and more snowy winters. Natural selection is powerless in face of sudden changes, as it can only modify things gradually. Further, selection only acts generally ; every animal does not survive that is modified in the desired direction. But that the modification can, generally speaking, advance

1 As mentioned in Weismann’s “ The Evolution Theory.” [English Translation.]

in this way is due to the fact that the material to select from is inexhaustible, and that immense periods of time are available for the process of transformation.

We see, therefore, that the changes that are brought about by natural selection, through the emphasising of insignificant characteristics, may become very striking. The external difference between grey and white hares is very considerable. It is true that one might claim the white hares to be a. variety of the grey ones, and say that the difference between the two forms is not as great as between the hare and the next species, the rabbit. But is there any difference between a “ variety ” and a “species”? Many writers understand by “ varieties ” animals with somewhat different features from those of the mother-species, but say that these characteristics vacillate, and are not preserved in the course of generations — are not constant , as the phrase is. We see that this test of the variety does not hold good in the case of our white hares ; the whiteness is constant, because all reversions are destroyed. And when it is said that the variety can always pair with the mother-species and produce fruitful offspring, which cannot take place between two different species, the statement is not entirely correct. Many species can be coupled, and beget young that are capable of reproducing. This is the case, for instance, with the wolf and the dog, the carp and the crucian, and other animals, which everybody recognises as distinct species.

We can safely affirm to-day that there are no rigid tests for determining whether certain types of animals are species or only varieties ; in other words, there is no sharp distinction between a species and a variety.

This modern discovery has thoroughly shaken the old Linnean principle : “ There are as many species as there were distinct forms created.” We now know that species are changeable, and have actually changed ; that one species may be formed from another. The question is often raised, in the form of an objection, why no species has been changed within our experience ; in fact, it is urged that history shows the forms of animals and plants to be just the same as they were 6,000 years ago, since the ancient Egyptians depicted lions and other animals just as we have them to-day. The objection seems to have some strength, but we know of several cases in which species have been so much modified within the historical period that they can no longer be crossed with their earlier relatives.

In the year 1419 rabbits were introduced on the isle of Porto Santo, near Madeira, and increased until they became a plague of the country. But the descendants have become very unlike their ancestors, and differ from them in their peculiar colour, rat-like shape, small size, nocturnal habits, and extraordinary savageness. But the most remarkable point is that they can no longer be crossed with the European rabbit, and have, therefore, formed a new species in this comparatively brief space of time.1

However, this was an exceptional case. The

1 The facts are related by Ernst Haeckel, who gave the Porto Santo rabbit the name of Lepus Huxleyi.

conversion of one species into another usually requires a longer period than the whole of human history, the 6,000 years of which are only an hour in comparison with the immense duration of the history of the earth. We saw above that it takes a long time for grey hares to become white ; and we know from geology that, as a matter of fact, all the terrestial epochs comprise enormous periods of time. The latest of them, the tertiary period, is calculated at several hundred thousand years. Geology also gives us the best idea of the mutability of species, as we find at the bottom of the sea the remains of animals of remote ages, which are totally different from the animals of our time. Geologists can distribute the various strata of the earth’s crust in their chronological succession. These strata are the pages of a book that it has taken millions and millions of years to write. Nowhere in it do we find the animals of our own time, or at all events only in the very latest periods of the earth’s history ; and the later the remains of extinct animals are, from the geological point of view, the closer do they come to the living fauna. It seems clear, therefore, that the animals of modern times were not present at the first creation of life, but only came into existence at a later date, and succeeded other animals in the dominion of the earth. But whence did they come so suddenly, if they were not evolved from other animals ? Every animal lies in the body of another before birth, in the form of an egg or ovum. But, clearly, before our animals appeared there were only forms of a different character ;

and therefore we may safely conclude that they have been evolved from these, and that in the course of generations the children have diverged more and more from their parents.

If we go further back in the story of the earth’s growth, we find that each period of geology has its characteristic animals, which must be the parents of the later and the offspring of the earlier forms. When, moreover, we pass in review before the eye of the mind the animals of the succeeding epochs, we notice something else besides the unceasing changes of form. The older the period we take, the simpler we find the shapes of living things ; and the nearer the period approaches to our own time, the more intricate and the higher is the organisation. In the earlier periods, for instance, we find only the lowest forms of vertebrates, and these only very sparingly. Gradually, the number of species increases. Lizards, birds, and mammals appear ; and amongst these the higher species come in succession, the carnivores, the apes, and, finally, at the last moment from the geological point of view, we find unmistakable proofs of man’s existence and activity.

Hence geology drives us to the conclusion that the animals of our time descend from simpler forms, these from yet simpler ones, and so on, so that only the very simplest organisms can have arisen at the first creation of living things. There was, for instance, a time when only the very lowest types of vertebrates, the fishes, were present on the earth ; and while a good many of these fishes were modified in the following epochs without going outside the range of the fish-class, others were so appreciably changed as to become salamanders. Geology shows, in fact, that at a certain period salamanders were the only vertebrates on the earth beside the fishes. We do not find these at the earlier stages ; they can only have been evolved from the fishes, as these are the nearest to them of all the animals that lived at the time, and the structure of the salamander approaches so closely to that of the fish that we can conceive the period as sufficient for the transformation — • a transformation which is far less considerable than the conversion of a worm into a salamander.

From these salamanders the actual salamanders and frogs must have descended on the one hand, and the reptiles, leading on to the birds and mammals, on the other. We may form a picture of the transformation of animals with the figure of the tree. At a certain period a side-branch, the fishes, grew out of the trunk ; the branch grew on, and put forth another side-branch, the salamanders, which in turn sent out branches. Thus we can compare the growth of the organic world with the growth of a tree. At first there was a single trunk, the simplest organisms. Branches grew out from the trunk, and in turn produced twigs, until a mighty tree arose with many branches and innumerable twigs.

The view that the animal kingdom was developed in this way from the simplest forms is called “ the theory of evolution.”1 It is now generally accepted ; there are

1 Also the theory of descent, or transformism. We must carefully distinguish between : i, the statement that living organisms have been developed from other forms , and 2, the theory as to how they were developed, and by what forces. The first is the theory of evolution, the few zoological and botanical works written to-day that do not rest on or presuppose this theory. An immense amount of proof in favour of it has been accumulated. Many predictions that were made on the strength of it have been realised by recent research, and prophecies of this kind are, when they are fulfilled, the very best proof of the correctness of the principles they are grounded on.

If, for instance, the birds were evolved from the reptiles, there must have been at a certain stage, since the tranformation was gradual, an animal intermediate between the reptile and the bird — an animal that was really a bird, but still retained unchanged many of the

second the theory of selection ; but there are a number of other theories with regard to the mode and agencies of development. These will be given later on. Hence those who accept the theory of evolution are not at all compelled to subscribe to the theory of selection ; in fact, there are many evolutionists who reject it. This will be quite clear if we remember that even in the Bible evolution is, in a certain sense, laid down as fact. It is stated in the Mosaic books that all the actual races of men, with their great differences in the colour of the skin, etc., descend from one couple. Hence theologians have seen of late that it is not advisable to reject evolution altogether. In particular, a Jesuit writer, Father Erich VVasmann, one of the first authorities on ants, has accepted the general theory of evolution in his work : “ Modern Biology and Evolution.” He holds that in the beginning God created a number of species at all stages of organisation, including man. But these species have not remained unchanged. They were endowed by the Creator with the capacity and the means of evolution. Thus we have an attempt to combine an acceptance of evolution with a belief in the verbal inspiration of Scripture. It is not likely to satisfy the man who seeks thoroughly to understand the world.

The theory of evolution was formulated before Darwin ; the theory of selection was created by him. But the theory of evolution itself owed its great advance to Darwin’s book, chiefly because he provided the explanatory hypothesis of selection. Hence it is not improper to include both theories under the title “ Darwinism.”

characteristics of the reptile. Now, we have found two well - preserved skeletons of a reptile - bird of this character. This “archaeopteryx” has the distinctive feathers, beak, pelvis, and feet of the bird, and at the same time an articulated lizard-like tail, teeth, and wellformed toes on its fore-feet, which project far out from the wing and are not found in any actual bird, but only in the reptiles.