Organic evolution as the result of the inheritance of acquired characters according to the laws of organic growth

Front matter

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ORGANIC EVOLUTION

*

Section II The Organic Growth Of The Living World 20

Fundamental Causes of the Manifold Variety of Organic Forms 22

Reproduction as Organic Growth . . . .24

Individual Development as Organic Growth . . .25

Separation of the World of Organic Forms into Species —

Genepistasis . . . . . .27

The Particular Causes which determine the Difference of the Directions of Evolution, and which also contribute to bring about the Division into Species . .32

Sexual Combination — One-sided Inheritance . . .35

Intermittent Evolution — Kölliker’s Hypothesis . . 45

Constitutional Impregnation . . . . .51

Elaboration and Simplification in the Evolution of Species . 52

XXVI

CONTENTS

Section III ■ Tage

INFLUENCE OF ADAPTATION IN THE FORMATION OF SPECIES 63

Is everything adapted ? . . . .63

Death as an Adaptation . . . . .67

Further Considerations on the Adaptation and Direction of Evolution of the Markings of Caterpillars. Absence of Sexual Combination in this Evolution . . .72

Characters which are inessential (indifferent) to the Life of the

Organism . . . . . .74

SECTION IV Methods of Investigation — The Period of Time to be claimed

for Evolution . . . . .78

Acquired Characters due to Direct External Action . . 87

Experiments on the Influence of Temperature on Lepidoptera . 116

Further Remarks on the Causes which Change the General

Colouring of Animals . . . . .135

Influences of Locality on the Variation of Animals, and thereby

on the Formation of Species . . . .139

Importance of the Stimulation of the Nervous System in

relation to Adaptation and the Origin of Species . 142

Particular Facts which prove the Influence of Nutrition and other external Conditions on the Variation and Formation of Species in Lepidoptera . . . .149

Characters acquired by Use . . . . . 153

Inheritance of Injuries and Diseases . . . .173

Section V Disuse Of Organs Degeneration— -pammixis 205

Pammixis

CONTENTS

XXVll

Section VI Page

MENTAL FACULTIES AS ACQUIRED AND INHERITED CHARACTERS 221

The Function of the Brain . . . . .221

Reflex Action ...... 222

Intelligence, Reason, Habit (Automatic Actions), Instinct . 223

Particular Instances of Intelligence and Reason in Animals . 231

Experiments and Observations on Instinct in newly-hatclied

The Instinct of the Cuckoo in Laying her Eggs in other Birds’

Reasoning Instincts . . . . . .266

Further Remarks on Reasoning Instincts and Intelligent In¬ stincts in Animals . . . . .278

Reflex Action and Instinct . . . . .294

Impulse and Instinct . . . . .301

Concluding Remarks on Instinct . . . .304

Irritability and Sensation — Will . . . .306

Section VII

ORGANIC GROWTH : THE MORPHOLOGICAL AND PHYSIOLOGICAL EVOLU¬ TION OF THE LIVING WORLD AS THE RESULT OF FUNCTION 315

The Origin of Organisation in Unicellular Animals — The

Fundamental Biological Law . . . .315

The Evolution of Organisation in Multicellular Animals . 323

Origin of Muscles . . . . . .326

Origin of Striation in Muscles . . . .328

Evolution of the various Sense-Cells from a Common Cell

The Origin of the Central Nervous System . . .339

Vicarious Nerve-Centres ..... 343

The Cell-Nucleus as a Central Nervous Organ . . 349

XXVI 11

CONTENTS

PAGE

Origin of Nerve-Fibres and their Vicarious Action . . 353

The Acquisition and Inheritance of Peculiarities of Voice and

Speech, and the Speech of Animals . . .362

Concluding Remarks . . . . .377

Section VIII The Idea Of Organic Growth - The Law Of Organic Form

RECRESCENCE 379

The Idea of Organic Growth . . . .379

Crossing and Selection as Indirect Causes of Growth . . 383

The Law of Organic Form : Its Application to the Form and

Structure of Plants . . . . .384

The Recrescence of Lost Parts as an Example of Organic Growth 389 Conclusion ....... 409

- APPENDIX

On the Idea of the Individual in the Animal Kingdom . 413

It seemed to me long ago of the greatest importance to under¬ take an investigation of the question whether the modification (variation) of the species of animals is not governed by definite laws.

It had previously been assumed that variation occurred quite irregularly, in the most diverse directions, that it was abandoned completely to chance ; in fact, the origin of species according to the Darwinian explanation is left entirely to chance. It was justly objected to that explanation that it asserted the predominance of chance. If, as I acknowledge, the principles of Darwinism are true because they can be shown to follow from natural laws, then it was to be expected that obedience to laws would also be discovered in that pro-' vince which Darwin had surrendered to chance. But if variation were shown to follow certain laws, the same demonstration would apply to the origin of species. For species have, as every evolutionist will acknowledge, of necessity been produced from varieties. They differ, if we can draw a dividing line between the two at all, from varieties only in this, that they are separated from related forms both upwards and downwards by the impossibility of unlimited fertile sexual intercourse, or else, as in the case of

B forms multiplying asexually, they are defined by conspicuous morphological characteristics.

But the investigation of the laws of variation included the question of the causes of this variation. In this respect also Darwin had left a great gap in the explanation of the origin of species. It was because he left variation essentially to chance that he was unable to say much on the question why it occurred at all. Indeed, it was the most zealous adherents of Darwin who made, and still make, the great mistake of treating the selection depending on utility as the power which by its own action brings forth those variations of the characters of the organism which afford the possibility of that selection ; or at least, the mistake of not perceiving clearly how far selection, how far Darwinism as a whole, is from being able to explain these variations.

The Darwinian principle of utility, the selection of the useful in the struggle for existence, does not explain the first origin of new characters. It explains only — and that in my opinion only partially — the progress and the gradually effected pre-eminence of these characters.

Darwin’s assertion that every character occurring in an organism must either be now useful to it, or must once have been useful, — an assertion which Darwin himself did not adhere to, but from which latterly he withdrew more and more, — has certainly more than anything else led to the false conception we have mentioned, for he set up utility as the only ruler in the organic kingdom. By the unconditional assumption of this supremacy it was quite overlooked that utility is a purely relative conception, and that therefore it cannot possibly be the fundamental principle of the forms of the organic world.

Before anything can be useful it must first be. Why, by wdiat means, is it brought into existence ? That is the wider question which I have put to myself.

But if there are agencies independent of utility which influence the forms of the organic world, which indeed primarily condition them, many characters of this organic world must exist which have nothing whatever to do with utility.

It was a 'priori to be expected that the result of my investigation would relate principally to such characters, hitherto but little considered.

If we could know all the natural laws which have operated in the evolution, and which operate in the existence of a single animal or a single plant, we should understand the laws of the organic world altogether.

On this ground alone the biologist may look for a rich reward in giving, himself unreservedly for once to the study of a single living being, in order to penetrate into its nature as deeply as possible. The single chosen object soon tells him more than all other animals or plants together which he has observed more superficially. For the more an investigator devotes himself to a fruitful object, the richer it appears to his eyes, the more it shows new properties, the more it acquires living interest and importance, and the more do all its characters and the relations of its life show themselves to be governed by law.

The unreserved study of a single species of animal has led me to the discovery of a whole series of laws, which the extension of the investigation to other species showed to hold good generally.

As far back as the beginning of the eighth decade of the present century, I had turned my attention to the wall-lizard, whose remarkable variability is well known, as the starting-point of my investigation. The circumstance that in the spring of 1872 I became acquainted with the dark blue wall-lizard, described by me as Lacerta muralis coerulea, on one of the Faraglione rocks at Capri determined my final decision.

In this form of the wall -lizard I had found an animal which might he with equal justice described as species or variety, so much does it differ from the original form. Thus, at the conclusion of the paper I published on this lizard,1 I was able to say : “ The remark of some opponents of Darwin¬ ism that no one has yet observed the conversion of a variety into a species is not, I grant, contradicted by the existence of the blue wall-lizard, for it makes on the adherents of the theory a demand similar to this : we want to hear the grass grow. Besides, every naturalist will always be at liberty, within cer¬ tain limits, to understand by a ‘ species ’ what he will. But an instance is afforded in this animal of undoubted natural raceproduction, which has evidently occurred in a relatively short period of time, and this ought to prevent any opposition, which is not expressly one of principle, from attaching any import¬ ance to the argument above quoted.”

The problem of finding the causes of the modifications which this remarkable variety had undergone led me im¬ mediately into the midst of the inquiries which I had already proposed to myself. The result of my researches, which were extended to various classes of animals, was the recognition of the dominion of laws in the process of variation, not only in the lizard, but also in the most diverse tribes of the animal kingdom : these laws holding firstly in the variations of marking, previouslyregarded as quite indifferent, unimportant, and fortuitous, but also applying to other characters. I was able to demonstrate that variation everywhere takes place in quite definite directions which are few in number, and I was able on the basis of my observations to put forward the view that the causes which lead to the formation of new characters in organisms, and in the last result to their evolution, consist essentially in the cliemico-physiological interaction between the material composition of the body and external influences.

1 Zoologische Studien auf Capri, ii. Lacerta muralis cccrulea, Leipzig, Engelmann, 1874,

.Finally, I succeeded, through the facts I established, in referring the separation into species, of which neither Darwin nor any of his successors had given a satisfactory explana¬ tion, in connection with the rest of my views, to natural causes.

I have expounded these views at full length in a second paper 1 on the variation of the wall-lizard.

But it seemed that very few investigators in the province of the doctrine of evolution troubled themselves about the wall-lizard, or about facts obtained from such a common animal, or about the conclusions to be drawn from them. It is possible, indeed, that the title of my papers was not very inviting. I ought to have put Darwinism first, and the wall-lizard second. Possibly the latter might then have been honoured too — possibly, for the tendency of the “ scientific ” zoology of to-day is to neglect the study of entire animals.2 Anything that is not teased with the needle, or cut with the microtome, or examined with the microscope, is scarcely noticed at the present day, except by those who are exclusively systematists, — even in questions connected with the evolution theory. For, strange to say, even the doctrine of evolution is left entirely in Germany to the decision of anatomy and em¬ bryology, that is, of the microscope, or else is given up to mere speculation, although Darwin himself, the reviver of this doc¬ trine, used neither the former nor the latter, but external

1 “ Researches on the Variation of the Wall-Lizard : a Contribution to the Theory of Evolution from Constitutional Causes, and also to Darwinism.” Arch, f Naturgeschichte , Berlin, 1881.

2 In the zoological Jahresbericht of the Zoological Station in Naples for 1881, published 1883, p. 219, I read: “Th. Eimer has published a very important paper, well worth reading, on the variation of the wall-lizard. This comprehen¬ sive memoir is not of a kind to be briefly summarised, and therefore the reader is referred to the original.” That is all the favourable acknowledgment of the memoirs in question which I have read up to quite recently, excepting reports in the Naturforscher and in the Revue der Naturwissenschaften. But K. Diising has just published a report showing complete comprehension of my meaning in vol. ii. of Kosmos of 1886.

form, the life and the distribution of plants and animals, for his theory.

No matter. In any case, since the publication of my papers various theories concerning evolution have appeared, whose authors have not troubled themselves in the least about the facts established by me, have not even mentioned them, although they contradicted their theories. But I will not go so far as to say with Nägeli that this was “ because they were unable to use these facts.” In an address to the second general meeting of the Congress of German Naturalists and Physicians at Freiburg i.B., which is printed as an appen¬ dix to this book, I had developed a theory based on facts. Subsequently, in various articles in the Zoologischer Anzeiger, and in the journal Humboldt , as well as in a lecture on the markings of birds and mammals1 delivered as early as 1882, which was afterwards published, and which is reproduced in the present book, I largely added to the number of these facts, and brought forward further irrefragable evidence for my views. But notwithstanding all this, not one of those who have set up theories or hypotheses of their own in our subject took any notice of my facts.

As we shall see, I have no special reason to complain in this matter. What has happened to me has happened to others. The botanist Nägeli makes, as I mentioned, the charge against such writers that they have not referred to the facts brought forward by him because they could not make use of them.

I might express myself in milder terms thus : The founders of theories of evolution set up since Darwin’s time have as a rule deviated from Darwin’s path, inasmuch as they have sought to adapt the facts to their ideas and opinions, instead

1 Ueber die Zeichnung der Vogel und Säugethiere. Lecture delivered at the Meeting of the “ Verein für Vaterländische Naturkunde in Württemberg” at Nagold on 24th June 1882. Württeviber gische naturwissenschaftliche Jahreshefte , 1883.

of adapting their ideas and opinions to the facts. Such argument leads naturally, even without any had intention, away from the consideration of the opposing facts back to its starting-point — revolving in a circle and seeing nothing which lies without the circle. This method is most surpris¬ ing in those who, like A. Wagner, with his Law of Migra¬ tion, oppose the whole of Darwinism in order to put in its place an explanation of evolution which can only find its place in Darwinism itself as a subordinate of that theory. Isolation in space, regarded by Wagner as alone regulating the origin of species, favours and promotes the separation of the gradu¬ ally produced diverse forms into species ; but apart from the truth that it does not alone explain the separation, its influence cannot possibly be put in the place of that of the principle of utility.

The effective influence is not necessarily single — many can be effective together.

On this standpoint I have placed myself in my inquiries from the first, and their course and their results have fully justified me.

On account of the relations which they bear to others, I have repeated some of the facts already published by me which serve as the foundation of my theory. The last sec¬ tions of this book are specially devoted to such facts.

It happens that my views on the question before us do not agree with those of some of my valued friends and honoured teachers, and if I am to uphold my own convictions I must endeavour to refute theirs.

As this opposition is little pleasing to myself, I am con¬ vinced that my frank advocacy of scientific opinions will neither by those who are aware of this personal relationship, nor by those who are immediately affected, be stigmatised as unfriendly and ungrateful.

Section I The Newest Theoeies Concerning Evolution

Before I proceed to the exposition of my own views I must briefly discuss some of those attempts to explain the evolution of organisms which have been made by others in recent years, namely, those of Weismann and Nageli.

The theory of heredity introduced by Weismann under the name “ Continuity of the Germ-plasm,”1 has recently been widely discussed, partly in a favourable, partly in an adverse spirit.2

This theory seeks to explain the fact that the characters of the parents are inherited to so high a degree by the children, and the other fact that characters can be inherited from more remote ancestors, e.g. from the grandparents,

1 A. Weismann, Die Kontinuität des Keimplasma als Grundlage einer Theorie der Vererbung, Jena, G. Fisclier, 1885. The same : Zur Frage nach der Vererbung erworbener Eigenschaften , Biolog. Centralblatt, 1886, Bd. vi. No. 2.

2 E.g. Naturforscher, 1886, No. 1. Eimer, Deutscher Litteratur zeitung, 15th May 1886. V. v. Ebner, Ueber Vererbung, Lecture delivered to the So¬ ciety of Physicians of Steiermark, 22d March 1886 ( Betz Memorabilien, 2 Heft7 1886). Külliker, Die Bedeutung der Zellkerne für die Vorgänge der Vererbung, Zeitsch.f. vj. Zool. 1885 ; and Das Karyoplasma und die Vererbung , eine Kritik der Weismanns 'dien Theorie von der Kontinuität des Keimplasma, ibid. 1886. Virchow, Descendenz und Pathologie, Arch. f. patholog. Anat. Bd. ciii. Kollmann, Biolog. Centralblatt, Bd. v. 1886. Virchow, Verhandlungen der Strass¬ burger Naturforscher Versammlung, 1885, Address delivered at the second general meeting of this Congress.

SEC. I

CONTINUITY OF GERM- PLASM one or more generations, e.g. the parents, being passed over (atavism).

Weismann’ s attempted explanation rests on the assump¬ tion that the germ cells, by means of which inheritance must be transmitted, pass over unchanged from the body of the ancestor into that of the descendant ; that they form a whole which so far contrasts strongly with the rest of the body ; that it takes no kind of part in the changes which the latter experiences during life ; that they can therefore be trans¬ mitted from generation to generation unchanged. G. Jäger 1 and Nussbaum2 had previously already sought to explain such an immediate connection between the germ-cells of parent and child, by the assumption that the germ-cells of the off¬ spring separated themselves at the very beginning of embry¬ onic development, or at all events before any histological differentiation, from the rest of the developing ovum.

According to Weismann — the assumption of Jäger and Nussbaum comes ultimately to the same thing — inheritance would be due to the fact that in every reproduction a part of the germ-plasm of the parental egg-cell is not used up in the construction of the offspring, but remains unchanged to serve for the formation of the germ-cells of the following generation. The inheriting substance lies, according to Weismann, in the contents of the nucleus of the germ-cell.

“The germ-cells,” says Weismann, “arise in their essential and distinctive substance, not by any means from the body of the individual, but directly from the parental germ-cells.” “ Inheritance,” he continues, “ takes place wholly and solely because a substance of definite chemical, and above all, molecular composition passes over from the germ -cells of one generation to those of the next. This substance, the

1 G. Jäger, Lehrbuch der allg. Zoologie , Leipzig, 1878, Bel. ii.

2 M. Nussbaum, Die Differenzirung des Geschlechts im Thierreich, Arch. f. mik Anat., 1880, Bd. xviii.

10 THE NEWEST THEORIES CONCERNING EVOLUTION sec.

germ-plasm, is located in the cell-nucleus, and possesses, by virtue of its extraordinary complexity of structure, the capacity to develop into a very complex organism.”

According to Weismann’s explanation of heredity, therefore, the germ-cells appear no longer as the product of the body, but rather as something in contrast with the totality of the body-cells. “ The germ-cells of successive generations are related in the same way as a series of generations of unicellular beings which are derived one from another by continued division.”

The necessary consequence of such a conception is the proposition that acquired characters are never inherited. If he is right, then no external influences whatever can ever have contributed to the moulding of species. The permanence of forms would be explained by that proposition, but their variability would remain, unless other agencies were brought forward for its explanation, a darker mystery than ever.

Weismann seeks these agencies in sexual reproduction.

By the mixture of characters which sexual reproduction brings about, according to him, are supplied at once — and exclusively — the materials for the origin of new species ; among the new forms produced by the mixture, the struggle for existence chooses the fittest for survival and for renewed reproduction.1

The great importance of the sexual mixing of characters in modification can be ignored by no one, and was indeed never ignored. But if this were the only cause of modification it would be necessary to assume, supposing the same laws to hold for lower as for higher organisms, that all plants and animals, including the lowest, now reproduce sexually, and always have done so, — an assumption which is known to be

1 A. Weismann, Die Bedeutung der geschlechtlichen Fortpflanzung für die Selektionstheorie , Address to the Congress of Naturalists at Strassburg, 1885, and Jena, G. Fischer, 1886.

I

VARIABILITY unjustifiable on the basis of the facts offered to us by the organic world now living, and which is contradicted by the general conception of the gradual development and perfection of organic differentiation. But Weismann compares the increase of the continually unchanged germ -plasm of the multicellular organism with the reproduction of the unicellular; in the latter also the same substance grows continually, and new individuals arise only by its division from time to time. The germ -plasm of the multicellular organisms is to correspond therefore with the whole body of the unicellular. Weismann does not deny that the unicellular beings change in consequence of the direct influence of external agencies ; on the contrary, he ascribes to them explicitly this property. From this inheritable individual diversity once produced he derives “that of the Metazoa and Metaphyta,1 in that this diversity, through sexual reproduction which has in the meantime become general, is preserved for ever, increased and ever produced in new combinations.” Thus, according to Weismann, the difference between the unicellular organism and the germ-plasm of the multicellular is a fundamental one — for the former other laws hold good than for the latter.

But against Weismann’s conception of the importance of the germ-plasm in heredity are to be set the following facts.

It is known that even highly organised animals and plants have the power of multiplying, by simple division in the case of the former, by cuttings in that of the latter.“ The new complete individual produced by this method has the same characters as the animal or plant produced at another time from a germ-cell — a proof that the substance possessing the property of heredity is not confined to the germ-plasm, and

1 I.e. of the multicellular animals and plants.

2 Cf. V. v. Ebner, op. cit.

12 THE NE J VE ST THEORIES CONCERNING EVOLUTION sec.

that it cannot be something altogether different from other parts of the organism.

When Weismann further expresses the opinion that sexual differentiation itself finds its explanation in his theory alone, he is to be met with the fact that such an explanation is certainly afforded by (1) the importance of preventing in-and-in breeding ; (2) the importance of division of labour.

Weismann’s argument against the inheritance of acquired characters seems to me to be abandoned by himself in his acknowledgment of the inheritance of the tendencies (pre¬ dispositions) to new characters acquired during life. In an article on this question1 I have remarked that any such tendency certainly implies a corresponding molecular peculiarity of the germ-plasm.

“ Let us assume,” I said, “ that all living beings have evolved one out of another, then, on the basis of Weismann’s conception itself, it must be acknowledged that the predis¬ position to the acquisition of characters, and with that the molecular structure of the germ-plasm, has in the course of time experienced great changes ; even with predispositions it is a question of characters acquired in the course of time and inherited.”

Further, Weismann grants a slight degree of inheritable external influence on the germ-plasm.

The greatest stress, however, is laid by him on the fact that no inheritance of injuries incurred during life has been proved.

That injuries incurred during life are but seldom trans¬ mitted to the offspring does not appear to me wonderful : the inheritance of the complete form and complete activities of the organism, which took root such enormously long periods of time ago, and has been strengthened at each generation, will as a rule counterbalance in the offspring any

1 Deutsche Litteraturzeitung , 15th May 1886.

I

NON-INHERITANCE OF INJURIES such injuries incurred only once and not repeated. It is true there are injuries which, although they have been always repeated constantly, are yet never inherited. Among these is the rupture of the hymen in women.

In such cases we must presume a specially effective power of correlative activity,1 directed to the part affected and residing in the whole organism — the same compensating power which leads in lower animals during the life of the individual to the regeneration of parts which have been lost or artificially removed.2 But these cases do not prove the general proposition that injuries are not inherited; they do not prove that even injuries which have been repeated during a considerable period are not inherited. Hitherto little importance has been attached to the demonstration of the inheritance of injuries. Yet single cases of the inheritance of injuries only once incurred seem to me to be thoroughly authenticated. To these I shall refer subsequently.

For the rest, it can I believe be proved as a fact that acquired characters are inherited.

The germ -plasm cannot possibly, in my view, remain un¬ touched by the influences which are at work on the whole organism during its life. Such an immunity would be a physiological miracle, merely on account of the morphological relations of the animal ovum and spermatozoon, and their dependence on the nutritive processes of the body,3 — a miracle

1 Correlation = the principle that the characters of the living being are so connected with one another that one determines the other.

2 The more imperfect the structure of animals, i.e. the lower their organisation, the less degree to which division of labour is carried out, so much the greater the facility with which injuries are repaired, so that many of the lower animals can be even cut into pieces with the result that each piece grows again into a perfect animal, just as in many plants. (Cf. on this point the Appendix : On the Idea of the Animal Individual.) The inheritance of injuries is thus of but slight importance in the discussion of heredity in general.

3 1 have myself described arrangements of quite surprising character for the nutrition of animal ova. Cf. my memoirs on the ova of Reptiles, Birds, and Fishes, in Arch, f mik. Anat. Bd. viii. 1872.

14 THE NEWEST THEORIES CONCERNING EVOLUTION sec.

which would he no less inexplicable than atavism, apart from WeismamTs theory, seems to be.

According to my ideas, it is not that sexual mixing of characters, together with adaptation, determines the modifica¬ tion of forms, hut rather that sexual differentiation itself is due to acquired and inherited characters.

But it is not my purpose at this point to bring forward all the arguments on which I rest my opposition to Weismann’s theory ; these arguments will he further developed in subse¬ quent pages.

A theory essentially opposed to Weismann’s regarding the causes of the modification of organic forms, in other words, the origin of species, has been set forth by Nägeli under the title “ Mechanico-physiological Theory of the Doctrine of Descent.” 1

According to him, internal causes depending on the nature of the organic substance effect the transformation of the “ strains ” (individuals, species, families, etc.) in definite direc¬ tions. Such “ internal causes ” must necessarily be supposed merely on the ground that the modifications or variations of the strains do actually take place in definite directions and are not irregular. The internal causes effect a constant altera¬ tion of the strains in definite directions ‘'towards greater perfection, that is, towards greater complexity.” The strains grow, as it were, towards greater perfection. Accordingly, dSTägeli describes his theory of internal causes as the principle of “ improvement.” “ Superficial reasoners,” he says, “ have pretended to discover mysticism in this. But the principle is one of mechanical nature, and constitutes the law of persist¬ ence of motion in the field of organic evolution.” “ Once the motion of evolution is started it cannot cease, but must persist in its original direction.”