The principles of heredity with some applications

Front matter

22102329235 l>a

Med

BY THE SAME AUTHOR

Preface

There is a good deal that is new — a little of which I hope will be found true — in this volume. It follows somewhat on the lines of my former work, The Present Evolution of Man, from which I have borrowed occasionally, especially in Chapter XI., and in the section devoted to Mind.

The evidence bearing on Heredity afforded by disease has hitherto been scarcely touched. It is utilized largely in the present work. I cannot help thinking that most students of Heredity are not aware of the value of this evidence from disease. I believe that if it had been considered in conjunction with the facts of specific adaptation to the environment a good deal of controversy concerning the transmission of acquirements and the origin of variations would not have occurred, or at any rate would not have lasted as long as it has done. So far as I am able to judge, it establishes conclusively the facts (1) that parental acquirements are never transmitted to offspring, and (2) that variations are rarely caused by the direct action of the environment on the germ-cells — so rarely that racial change is never due, directly or indirectly, to this cause. The great mass of variations have another origin which I have endeavoured to elucidate.

The function of bi-parental reproduction appears to me manifest. It is very important, but it has nothing to do with the causation of progressive variations.

In the fifth chapter I have sought to re-establish on a firm basis the doctrine that the development of the individual is a blurred recapitulation of the life-history of the race. The doctrine of recapitulation has been controverted of late ; but in the whole range of biology there is nothing that is more certainly true. It follows logically and necessarily from the known fact that the child recapitulates the developmental footsteps of the parent. Unless it were true there could be no development of the individual and no evolution of the race. This fifth chapter is the crux of the whole work. If the scientific reader finds its reasoning correct and its conclusions

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valid, he will probably not raise much objection to the rest of the book.

I have addressed the volume mainly to medical men. The

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PREFACE evidence relied on is drawn largely from medical sources ; medical men form the largest body of scientific workers ; they deal constantly with questions of Heredity, a knowledge of which is of great importance to them ; but in a measure they have neglected the systematic study of the subject. Little or no direct instruction in it is given to medical students. There does not exist even a text-book to which they may refer. But a knowledge of Heredity is becoming essential to the educated doctor. I have sought to supply the want. I hope, however, the professional biologist and the general reader will not find the work devoid of interest. I have tried throughout to give prominence to broad generalizations rather than to isolated facts, to found my conclusions wholly on verified evidence, and to write in such a way that the reader’s task will not be unnecessarily toilsome.

My hearty thanks are due to Dr. Gerald Leighton for “going over” the first fifteen chapters, and to the Editors of The Monthly Review and The Lancet for permission to adapt for Chapter X. matter which had appeared in their pages.

Preface To Tlie Second Edition

The first edition of this work has been exhausted with such unexpected rapidity that I have been unable to make alterations of importance in the body of the book. A better definition, or description, of “ spontaneous ” variations has been introduced on page thirty-eight. Numerous typographical errors have been corrected, for the discovery of which my thanks are due to several correspondents. The main addition to the first issue consists, however, in two somewhat lengthy appendices. In the first, besides the discussion of one or two allied questions, I have endeavoured to make clearer the all-important distinction between innate and acquired characters. In the second I have dealt in some detail with the mutation theory of evolution and the phenomena of alternative inheritance. Several reviewers, notably that most indulgent of all critics, Dr. C. W. Saleeby, have expressed the opinion that the labours of Mendel and his followers have not been adequately discussed by me. I have tried to rectify the omission.

Southsea, 4th Dec., 1905.

ERRATA

Page 56, eighteenth line, for diseased read deceased.

,, 358, last line, for albumen read cotyledons.

,, 365, fourth line from bottom of text, delete greater. ,, 372, fifth line, for inter-varietal read intra-varietal.

Chapter I Theories Op Heredity

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Definition of Heredity — The multiplication of cells — The Germ-plasm — The characters of living beings — Inborn characters — Acquired characters — Modi fications — V ariations — The Lamarckian doctrine of Heredity 1

Chapter II Theories Op Evolution

The Bathmic Theory — The Lamarckian Theory — Tke Neo- Darwinian Theory — -The alleged inheritance of acquired characters — Mutilations — Maternal impressions — Diseases .... 13

Chapter III

Regeneration — Adaptive acquirements — The co-ordination of animal parts — The effects of use and disuse — The evolution of the power of making adaptive acquirements 29

CHAPTER IV Variations attributed to the direct action of the environment

Some variations at least arise otherwise — The evidence that variations are caused by external influences — Reasons for believing they are not so caused — Variations said to be caused by bi-parental reproduction — The principal forms of bi-parental inheritance— Evidence that bi-parental reproduction is a cause of variations . 38

Chapter V

The recapitulation of the parental development — The consequent recapitulation of the life-history of the race — Neglect of the doctrine of recapitulation by students of heredity — Regressive and progressive variations — Reversion the same thing as regression — Dormant traits — Reversed Selection 52

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Chapter VI P Age

Bi-parental reproduction said to be a cause of progressive variations— A complete error — Evidence from the common experiences of life — The scientific evidence — Equidse— Pigs — Goats — Rabbits — Sheep — Pigeons — Fowls — Ducks — Plants — Reversion seldom observable under conditions of Natural Selection — Often observable under conditions of artificial selection — Reversion the cause of the deterioration of useless parts — The function of bi-parental reproduction in evolution 67

Chapter VII

Summary — The function of regression in evolution — Development in ancient environments — Development in new environments— The evolution of man’s higher faculties — The “ inadequacy of Natural Selection” — The unknown factor — Theories of regression — Germinal selection 86

Chapter VIII

The inherent tendency to vary— Galton’s law of inheritance — In-breeding and cross-breeding — Fertility and sterility — The effects of domestication on fertility — The geographical distribution of species — Summary 95

Chapter IX

The alleged Cessation of Selection among civilized peoples— Civilized man is stringently selected — A problem for medical men — Inborn and acquired immunity — Doctrines of heredity as applied to problems of disease 106

Chapter X

■/ Theories of immunity — The kind of diseases against which immunity may be acquired — Pasteur’s theory — Chauveau’s theory —

The theory of chemical neutralization — The theory of habituation — Rabies — Small-pox — Anthrax — Snake-venom — The rationale of acquired immunity — Syphilis 115

Chapter XI

The decisive evidence afforded by disease — Malaria — Tuberculosis— Measles — Whooping-cough — Small-pox — Dysentery — Diarrhoea— Enteric fever 134

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Chapter XII

The Lamarckian doctrine is certainly untrue — It is equally untrue that hereditary tendencies may be easily changed by the direct action of external forces — Professor Cossar Ewart’s observations

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Chapter XIII

The microbes of disease are an infinitesimal portion of the total number of bacteria — Men acquire microbic diseases as a rule only from other men — The conditions necessary for the evolution of a microbic disease — The antiquity of microbic diseases — Their first origin — Their spread — Earth-, air-, and water-borne diseases — Epidemic and endemic disease — Epidemics in the ancient and modern worlds 168

Chapter XIV

Air- and water-borne diseases in the Western Hemisphere — Tuberculosis — The extinction of the natives — The colonization of the New World by European nations — The causes of success or failure — The foundations of empire — The cessation of the great migrations 182

Chapter XV

A mental problem — The elimination due to alcohol — The reasons why men drink — Self-control — Will-power — Variations amongst drinkers — Alcoholic selection — Racial differences — Alcoholic evolution — Is parental intemperance the cause of filial degeneration! — Opium — The sobriety of South Europeans — The comparative drunkenness of North Europeans — The excessive drunkenness of some savages — The sobriety of others — Intemperance in the ancient world — Climate — Potency of beverages — Environment — The memory of past disasters — Civilization — Education — The parallel between diseases and narcotics . .189

Chapter XVI

Mental symbols — The origin and evolution of mind — Sense-impressions— Feelings — Pleasure and pain — The will . . . 209

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Chapter XVII

Instinct — Reason — Memory — Sitaris — Dragon-fly — The instincts of Man — The evolution of Memory and Reason — Animals that tend their young — Social animals — The ant — Traditional knowledge in the lower animals — Comparison of the frog with the human being .

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Chapter XVIII

The essential difference between Man and the brutes — Reason in the brutes — The substitution of reason for instinct — The instincts of Man — The sexual instinct— The parental instinct — The instinct for food — Imitativeness — The sporting instinct — The stereotyping of mental acquirements — Its advantages and disadvantages 235

Chapter XIX

All “ inborn ” characters are in reality acquirements — All automatic actions are voluntary — They result from “ diffused,” not concentrated attention 248

Chapter XX

All instinctive actions are voluntary — They differ from rational actions only in that the tendency and (as a rule) the capacity to perform them are inborn — Lewes — Spencer — Romanes — Mental acquirements are not transmissible — Offspring are not affected mentally by the action of the environment on the parental germ-plasm 261

Chapter XXI

The basis of Man’s mind — The physical changes which have accompanied the evolution of memory — Speech — The substitution of acquirements for instincts — Sexual and parental love — Modesty — Morality — Comparison between physical and mental traits — Mental acquirements that are due to physical conditions — The influence of the environment — Man the edueable animal — The opinions of scientific men . , ... 272

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Chapter XXII

Mainly acquired — Differences in instinct must be slight — Shapes and sizes of brains in relation to intelligence — The stability of inborn characters — Most racial characters cannot be inborn since they are liable to too rapid alteration — The evidence from religion

Chapter XXIII

The ways in which religions mould character — Dogmatic and rational teaching — The mental uniformities and divergencies caused by religious sects — The mental characteristics of the Greeks and Romans — Of the Early Christians — Of Christians during the Dark Ages — Of Heretics— Progress — Enlightenment— The proportion of great men

CHAPTER XXIY

The evolution of the hunting instinct — The reason why labour is unpleasant — The formal education of the lower classes — That of the higher classes — Classical teaching — The decay of the patrician classes — Scientific teaching — -Artificial aids to memory and the reasoning faculty — The teachings of the principles of heredity — The training of medical men

Chapter XXV

Physical deterioration — The influence of urban conditions on the race — Public health — Water-, Earth- and Air-borne diseases — Intemperance — Child-birth— Insanity

Appendix A. — Characters, inborn and inherited .

Appendix B. — Mendel’s Laws, and the Mutation Theory of Evolution •

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Index .

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Chapter I

Definition of Heredity — The multiplication of cells — The Germ-plasm — The characters of living beings — Inborn characters— Acquired characters — Modifications — Variations — The Lamarckian doctrine of Heredity.

1. Heredity has been variously defined. Herbert Spencer describes it as “ the capacity of every plant and animal to produce other individuals of a like kind.” Weismann follows Spencer very closely. According to him “ the word heredity in its common acceptance means that property of an organism by which its peculiar nature is transmitted to its descendants.” The science of heredity may be defined as that science which deals with the organic relationships of progenitors with descendants.

2. The systematic study of heredity is of very recent origin. It dates, in effect, from the publication of Darwin’s great work The Origin of Species. No doubt many important facts were known previously ; and Lamarck, Spencer, and others had formulated theories of evolution which implied theories of heredity. But so much of error was mingled with the facts, and so much of ancient superstition incorporated with the theories, that a great part of the value of both was lost. The interest aroused by Darwin’s speculations gave the necessary stimulus. A body of earnest and in many cases brilliant workers strove to increase the sum-total of our accurate knowledge, to dig the truth out of the accretions of fiction which had gathered round it during the process of ages. To-day enough is known with certainty to justify the erection of heredity into a study which is by no means the least important of that group of studies which we gather

B under the general name of biology. The work has been done chiefly by zoologists and botanists, but, probably, heredity concerns medical men more nearly than any other body of scientific workers. Evidence is not wanting that the period of professional neglect is drawing to a close, and that, ere long, a systematic knowledge of the laws which control the reproduction of living beings will be considered as necessary a part of the equipment for the struggle against disease as anatomy or physiology.

3. The material for the study of heredity already in the possession of medical men is so valuable that there can be little doubt that both medicine and heredity have suffered from the failure to collect and apply it in a systematic way. A knowledge of the natural history of the being to whom he devotes his life is essential to the medical worker. No zoologist or botanist can possibly have a knowledge of any animal or plant so detailed and extensive as the educated physician possesses of his own species. No experiments devised by man can rival in scope and magnitude, in duration and stringency, the many and vast experiments conducted by nature through the medium of disease. An attempt will be made in the present work to systematize and apply a portion at least of this rich mass of material. No doubt, through lack of knowledge or of judgment, the writer will frequently do less than justice to his subject. His task is one of considerable difficulty and magnitude. But his very failures may stimulate future workers to tread more successfully the path that he seeks to indicate. If he is able to preserve the interest of his readers during the first few chapters it should be possible to sustain it afterwards. There is more for medical men in the study of heredity than is commonly supposed.

4. At the present day educated men are agreed that all forms of life are related to one another through an ancestry, which, in the case of the more divergent forms, is very remote ; and that all the higher and more complex forms have been evolved from lower and more simple forms.1 The only question really in dispute among people acquainted with the facts is the method by which evolution has proceeded. The correct elucidation of that method involves the discovery of the right doctrine of heredity.

1 Evolution within limits has been tacitly admitted by nearly all peoples and creeds. Thus it is almost universally believed that all races of mankind have sprung from a common stock. Human races are now very divergent, and each race is especially adapted to the environment in which it has spent its past.

5. The basis of all known life is the cell. The typical cell consists of a nucleus and a cell-body. It has been proved beyond reasonable doubt that the nucleus, or rather a hypothetical substance within it which has been termed the “ germ-plasm,” is “ the bearer of heredity.” Some such substance — some substance which is the bearer of heredity — there must be of necessity. Cells multiply by dividing into two or more daughter cells, the usual number being two. The lowest plants and animals are single cells. Higher organisms consist of two or more — it may be billions — of cells united for the common good. The body of a multicellular plant or animal is compounded of the cell-descendants of a unicellular organism, which is usually a fertilized ovum. Each cell of the body, though definitely related to its fellows, is, in a very real sense, a distinct and separate living entity — a unicellular organism. Blood-cells and wandering connective tissue-cells are free. Spermatozoa and ova are purely parasitic. Skin cells have been artificially transplanted. Had we the requisite skill it is possible that we could transplant every kind of cell. The death of the whole organism (somatic death) is followed, only after a measurable interval, by the death of its component cells.

6. Watching the multiplication of a somewhat highly organized unicellular animal (, Stylonychia joustulata, an infusorian), JVIaupas observed that after two of these had conjugated, the resulting fertilized cell divided and re-divided many times without conjugation occurring again ; but that if, after a certain fairly definite number of cell-divisions, during which millions of individuals had come into being, conjugation did not occur again, the family ultimately died out. He found, moreover, that the descendants of a conjugated pair did not conjugate among themselves, but only with the members of another family, the descendants of another conjugated pair.1

7. Now all this is the rule amongst higher plants and animals. The ovum and the sperm are unicellular animals of the same species. They differ in appearance, for the large and passive ovum contains much nutriment, whilst the small and active sperm carries an organ of locomotion ; but in essentials they agree. Their nuclei are equivalent ; that is

1 Arch. cl. Zool., 2me s4rie, vii. 1889. Calkins, who has repeated Maupas’s experiments, disputes some of his conclusions. For example, he claims to have proved that infusorians, if properly nourished, continue to multiply indefinitely without conjugation. This point, as the reader will perceive later, is not material so far as the present work is concerned.

they are equally bearers of heredity.1 After the conjugation of the ovum and the sperm the resulting cell divides and re-divides many times without conjugation occurring amongst the descendant cells. These, like infusorians, if they do not conjugate, ultimately die out. Most of them (the somatic or body cells) are incapable of conjugation ; whilst such of them as are capable of conjugation (the germ-cells) conjugate only with cells from another body (i. e. cell family). There are, as is well known, exceptions to this rule. Apparently unending multiplication of cells may occur without conjugation, as among such plants as are propagated by buds, slips, and suckers ; and self-fertilization also occurs ; but the general rule is as stated. A multicellular plant or animal, in the successive stages of its development, is to be regarded, therefore, as the homologue, not of the remote ancestral organism, the homologue of which is the ovum or the sperm, but of all those successive generations of unicellular organisms which intervene between one act of conjugation and the next.

8. On the other hand, the cell-descendants of a pair of conjugated germs differ from the cell-descendants of a pair of conjugated unicellular organisms in that (1) they remain united and work together for the common good, (2) they undergo differentiation of form and specialization of function along certain definite lines of descent (into bone, muscle, gland and other cells), the germ-cell being specialized, for the reproduction of the complex multicellular organism, and (3) they multiply in different lines of descent at unequal, though definite, rates. Did the cell-descendants of the fertilized ovum all multiply at an equal rate, a solid spherical mass of cells would of course result ; whereas, owing to differences in their rates of multiplication, the shapes of multicellular plants and animals are irregular (he. not spherical). But, though these rates of multiplication are pretty definite in every species of plant and animal, they differ widely in different species — whence arise differences in shape betwixt one species and another. An ox, for instance, differs in shape from a man because in it the

1 The nucleus was formerly regarded as a non-essential portion of the germ-cell. It is now beyond doubt that it — or rather the chromatin contained within it — is the sole “ bearer of heredity.” Except that they are derived from male and female bodies there is nothing male or female in the nuclei of germ-cells. All this was decisively proved by one of Boveri’s experiments. He separated by shaking the nucleus from the ovum of one species of Echinus and then fertilized the enucleated ovum with spermatozoa from another species. The larva which resulted developed the true characters of the last species only.

cells, in the different lines of descent, do not multiply at the same rate as in man.

9. All evolution consists, in essence, of a gradual change in the character of the germ-plasm contained in successive germ-cells — a change of such a nature that it is reflected in the successive individuals that spring from the cells. Thus, if, by careful breeding, we succeed in altering any plant or animal species, it is only because we have succeeded in altering to a corresponding extent the nature of the germ-plasm of that species.

10. All the traits or characters (the terms are synonymous) of every living being are separable in theory, if not always in practice, into two distinct categories. Either they are inborn or they are acquired. The first essential to a study of heredity is a clear comprehension of the distinction between inborn and acquired characters. Inborn traits or characters are those ivhich talee origin in the germ-plasm , which arise because the germ-plasm is so constituted that it tends, under fit conditions of shelter and nutrition, to impel or cause the germ-cell to proliferate into an individual having those characters. Thus a man’s head is inborn. It arises because the germ-plasm in the fertilized ovum whence he sprang was so constituted that it impelled that germ-cell to proliferate into a being having a man’s head. Acquired characters, on the other hand, do not take origin in the germ-plasm ; they are modifications of inborn characters caused by the play of forces from the environment on those characters after (as a mole) they have developed from the germ-cell. Thus a man’s hand is inborn. But if it be modified by use, disuse, accident, or the play of other forces from the environment the modification is an acquired character.1 Inborn characters take origin in the germ ; that is, they are blastogenetic in origin. They express the hereditary tendencies of the individual, and, with variations, those of the race. Acquired characters take origin (as a rule) in the cell-

1 “ All the effects of exercise are acquirements — for example, the enlargement which exercise causes in muscles. The effects of lack of exercise are also acquirements — for example, the wasting of a disused muscle. The effects of injury are acquirements — for example, the changes in a diseased lung or an injured arm. Every modification of the mind is also an acquirement — for example, everything stored within the memory. If a man be blinded by accident or disease his blindness is acquired. But if he come into the world blind, if he be blind “ by nature,’’ his blindness is inborn. If a son be naturally smaller than his father, his inferiority of size is inborn ; but if his growth be stunted by ill-health or lack of nourishment or exercise, his inferiority is acquired.” ( Alcoholism . A Study in Heredity, p. 9.)

descendants of the germ-cell ; that is, they are somatogenetic in origin. They express the modifications of the hereditary characters of the race which are caused in the individual by the play of forces from the environment.

11. The main mass of inborn or congenital characters are ancient heritages of the race. Thus head, heart, limbs, lungs, liver, the various organs of sense, etc., were possessed by the race of man even before it became human. But, since every individual differs congenitally somewhat from his parents, therefore every individual exhibits some new inborn characters. These are usually slight alterations of pre-existing inborn characters — an increased or decreased thickness or hairiness of the skin, a larger nose, a smaller mouth, a stronger heart, a weaker digestion, a broader foot, a narrower hand, a keener sight, a duller hearing, and so forth. Occasionally, however, new inborn characters are of considerable magnitude ; or they may not be mere alterations of old characters, but entirely new structures. Such new excessive inborn characters are termed abnormalities. Thus a man may be born very much smaller or bigger, weaker or stronger, than his parents ; or a child of normal parents may be born with a sixth digit on one hand, or deaf, or with a defective heart. All new inborn characters, great or small — all new characters which take origin in the germ-plasm, which are congenital, which come to the individual “ by nature,” which are inherent in him, which are expressions of his hereditary tendencies— are technically termed “ variations." On the other hand, all acquired characters — all alterations in an individual caused by the play of external forces on his inborn characters, all such characters as are not congenital in him, such as do not arise in him “ by nature,” such as do not imply a corresponding and pre-existing trait in the germ-plasm, such as do not express his hereditary tendencies — are technically termed “ modifications ” or “ acquirements .”

12. The precise technical meaning of these expressions — inborn, congenital, variation, acquirement, modification — must be noted. They have not in biological literature the extended and ambiguous significations which they possess in popular literature. At any rate they are intended to have very precise and definite meanings in the present work. Formerly it is true that the term “ variation ” was used indifferently to indicate all differences, inborn or acquired, between parents and offspring, but of late years most authorities have agreed to limit the term to inborn differences alone. The word “ congenital ” is generally used as synonymous with inborn, and will be so used in the present work ; but by medical men, especially, it is sometimes applied to traits which appear before birth as distinguished from those which appear afterwards. From the point of view of heredity, however, since characters may be acquired in utero , the episode of birth is of no importance. It is necessary to define these terms exactly, for otherwise the most desperate confusion is apt to occur and indeed has very often arisen.1 Their importance is due to the fact that, while it is admitted on all hands that inborn traits (including variations) tend to descend from parents to offspring and to more remote descendants, it is now denied by the vast majority of biologists that “ modifications ” are ever inherited. Thus, while it is admitted that if a man be blind “ by nature ” his blindness will very probably descend to his offspring, it is denied if he acquire blindness (as by injury, for instance) that his defect will tend to be inherited.

1 If once we apprehend clearly the fact that the difference between the inborn and the acquired is one of origin we shall avoid many of the grotesque errors which vitiate the writings of some popular authors who have dealt with this subject. Even when heredity is discussed in medical meetings some one is pretty sure to remark with an air of finality, “ Acquired characters must be transmissible, for every character must have had a beginning, and therefore must have been acquired originally.” This sentence is such a triumph of inaccurate statement and loose thought, and within its brief limits sets forth so neatly the principal source of confusion prevalent in popular and medical terminology, that it is worth while to examine it at length. It assumes that the difference between the inborn and the acquired is not one of origin, but one of age, and that, therefore, all old characters are inborn, and all new characters are acquired. But language and bipedal locomotion are very old characters in man : yet they remain acquirements, for every man still learns to talk and walk. Acquired immunity against this or that disease is another old character ; it also remains an acquirement, for every man who acquires immunity acquires it afresh. On the other hand, to term a new character an acquirement merely because it is new is an absurdity for more reasons than one. In the first place the words “ inborn ” and “ acquired ” are well-established technical terms with very precise and definite meanings. Biologists use them to mark the vitally important distinction between blastogenetic and somatogenetic characters. An argument which is based on a misuse of terms does not commend itself as conclusive from a scientific point of view. In the second place the distinction between the new and the old is, in this connection, a valueless one. Every character is new to the individual who has it. Thus a man’s head is as new to him as a sixth digit or any other variation from the parental type. In the third place the whole argument is beside the mark, for the fact that some new characters are transmissible has never been disputed. On the contrary, the fact that they are transmissible is the corner-stone of every theory of heredity. It is admitted on all hands that new inborn characters are transmissible — new characters, that is, which take origin in the germ-plasm. All that has ever been disputed is that somatic modifications, whether new or old, are transmissible.