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THE WHENCE AND THE WHITHER OF MAN
A Brief History of His Origin and Development through Conformity to Environment
Being the Morse Lectures of 1895
by
JOHN M. TYLER Professor of Biology, Amherst College
New York Charles Scribner's Sons
1896
Morse Lectures
1893—THE PLACE OF CHRIST IN MODERN THEOLOGY. By Rev. A.M. Fairbairn, D.D. 8vo, $2.50
1894—THE RELIGIONS OF JAPAN. By Rev. William Elliot Griffis, D.D. 12mo, $2.00.
1895—THE WHENCE AND THE WHITHER OF MAN. By Professor John M. Tyler. 12mo, $1.75.
TABLE OF CONTENTS
INTRODUCTION
CHAPTER I
THE PROBLEM: THE MODE OF ITS SOLUTION
The question.—The two theories of man's origin.—The argument purely historical.—Means of tracing man's ancestry and history.—Classification.—Ontogenesis and Phylogenesis.
CHAPTER II
PROTOZOA TO WORMS: CELLS, TISSUES, AND ORGANS
Amoeba: Its anatomy and physiology.—Development of the cell.—Hydra: The development of digestive and reproductive organs, and of tissues.—Forms intermediate between amoeba and hydra: Magosphaera, volvox.—Embryonic development.—Turbellaria: Appearance of a body wall, of ganglion, and nerve-cords.
CHAPTER III
WORMS TO VERTEBRATES: SKELETON AND HEAD
Worms and the development of organs.—Mollusks: The external protective skeleton leads to degeneration or stagnation.—Annelids and arthropods: The external locomotive skeleton leads to temporary rapid advance, but fails of the goal.—Its disadvantages.—Vertebrates: The internal locomotive skeleton leads to backbone and brain.—Reasons for their dominance.—The primitive vertebrate.
CHAPTER IV
VERTEBRATES: BACKBONE AND BRAIN
The advance of vertebrates from fish through amphibia and reptiles to mammals.—The development of skeleton, appendages, circulatory and respiratory systems, and brain.—Mammals: The oviparous monotremata.—Marsupials.—Placental mammals.—Development of the placenta.—Primates.—Arboreal life and the development of the hand.—Comparison of man with the highest apes.—Recapitulation of the history of man's origin and development.—The sequence of dominant functions.
CHAPTER V
THE HISTORY OF MENTAL DEVELOPMENT AND ITS SEQUENCE OF FUNCTIONS
Mode of investigation.—Intellect.—Sense-perceptions.—Association. —Inference and understanding.—Rational intelligence.—Modes of mental or nervous action.—Reflex action, unconscious and comparatively mechanical.—Instinctive action: The actor is conscious, but guided by heredity.—Intelligent action.—The actor is conscious, guided by intelligence resulting from experience or observation.—The will stimulated by motives.—Appetites.—Fear and other prudential considerations.—Care for young and love of mates.—The dawn of unselfishness.—Motives furnished by the rational intelligence: Truth, right, duty.—Recapitulation: The will, stimulated by ever higher motives, is finally to be dominated by unselfishness and love of truth and righteousness.—These rouse the only inappeasable hunger, and are capable of indefinite development.—Strength of these motives.—Their complete dominance the goal of human development.
CHAPTER VI
NATURAL SELECTION AND ENVIRONMENT
The reversal of the sequence of functions leads to extermination, degeneration, or, rarely, to stagnation.—Natural selection becomes more unsparing as we go higher.—Extinction.—Severity of the struggle for life.—Environment one.—But lower animals come into vital relation with but a small part of it.—It consists of a myriad of forces, which, as acting on a given form, may be considered as one grand resultant.—Environment is thus a power making at first for digestion and reproduction, then for muscular strength and activity, then for shrewdness, finally for unselfishness and righteousness.—An ultimate "power, not ourselves, making for righteousness," a personality.—Our knowledge of this personality may be valid, even though very incomplete.—Religion.—Conformity to the spiritual in or behind environment is likeness to God.—The conservative tendency in evolution.
CHAPTER VII
CONFORMITY TO ENVIRONMENT
Human environment.—The development of the family as the school of man's training.—The family as the school of unselfishness and obedience.—The family as the basis of social life.—Society as an aid to conformity to environment by increasing intelligence and training conscience.—Mental and moral heredity.—Personal magnetism.—Man's search for a king.—The essence of Christianity.—Conformity to environment gives future supremacy, but often at the cost of present hardship.—Conformity as obedience to the laws of our being.—Environment best understood through the study of the human mind.—Productiveness and prospectiveness of vital capital.—Faith.
CHAPTER VIII
MAN
Composed of atoms and molecules, hence subject to chemical and physical laws.—As a living being.—As an animal.—As a vertebrate.—As a mammal.—As a social being.—As a personal and moral being.—The conflict between the higher and the lower in man.—As a religious being.—As hero.—He has not yet attained.—Future man.—He will utilize all his powers, duly subordinating the lower to the higher.—The triumph of the common people.
CHAPTER IX
THE TEACHINGS OF THE BIBLE
Subject of the Bible.—Man: Body, intellect, heart.—God: Law, sin, and penalty.—God manifested in Christ.—Salvation, the divine life permeating man—Faith.—Prayer.—Hope.—The Church.—The battle.—The victory.—The crown.
CHAPTER X
PRESENT ASPECTS OF THE THEORY OF EVOLUTION
The struggle for existence.—Natural selection.—Correlation of organs.—Fortuitous variation.—Origin of the fittest.—Naegeli's theory: Initial tendency supreme.—Weismann and the Neo-Darwinians: Natural selection omnipotent.—The Neo-Lamarckians.—Comparison of the Neo-Darwinian and the Neo-Lamarckian views.—"Individuality" the controlling power throughout the life of the organism.—Transmission of special effects of use and disuse.—Summary.
CHART SHOWING SEQUENCE OF ATTAINMENTS AND OF DOMINANT FUNCTIONS
PHYLOGENETIC CHART OF THE ANIMAL KINGDOM
INDEX
INTRODUCTION
In the year 1865 Professor Samuel Finley Breese Morse, to whom the world is indebted for the application of the principles of electro-magnetism to telegraphy, gave the sum of ten thousand dollars to Union Theological Seminary to found a lectureship in memory of his father, the Rev. Jedediah Morse, D.D., theologian, geographer, and gazetteer. The subject of the lectures was to have to do with "The relations of the Bible to any of the sciences." The ten chapters of this book correspond to ten lectures, eight of which were delivered as Morse Lectures at Union Theological Seminary during the early spring of 1895. The first nine chapters appear in form and substance as they were given in the lectures, except that Chapters VI. and VII. were condensed in one lecture. Chapter X. is new, and I have not hesitated to add a few paragraphs wherever the argument seemed especially to demand further evidence or illustration.
One of my friends, reading the title of these lectures, said: "Of man's origin you know nothing, of his future you know less." I fear that many share his opinion, although they might not express it so emphatically.
It would seem, therefore, to be in order to show that science is now competent to deal with this question; not that she can give a final and conclusive answer, but that we can reach results which are probably in the main correct. We may grant very cheerfully that we can attain no demonstration; the most that we can claim for our results will be a high degree of probability. If our conclusions are very probably correct, we shall do well to act according to them; for all our actions in life are suited to meet the emergencies of a probable but uncertain course of events.
We take for granted the probable truth of the theory of evolution as stated by Mr. Darwin, and that it applies to man as really as to any lower animal. At the same time it concerns our argument but little whether natural selection is "omnipotent" or of only secondary importance in evolution, as long as it is a real factor, or which theory of heredity or variation is the more probable.
If man has been evolved from simple living substance protoplasm, by a process of evolution, it will some day be possible to write a history of that process. But have we yet sufficient knowledge to justify such an attempt?
Before the history of any period can be written its events must have been accurately chronicled. Biological history can be written only when the successive stages of development and the attainments of each stage have been clearly perceived. In other words, the first prerequisite would seem to be a genealogical[A] tree of the animal kingdom. The means of tracing this genealogical tree are given in the first chapter, and the results in the second, third, and fourth chapters of this book.
[Footnote A: See Phylogenetic Chart, p. 310.]
Now, for some of the ancestral stages of man's development a very high degree of probability can be claimed. One of man's earliest ancestors was almost certainly a unicellular animal. A little later he very probably passed through a gastraea stage. He traversed fish, amphibian, and reptilian grades. The oviparous monotreme and the marsupial almost certainly represent lower mammalian ancestral stages. But what kind of fish, what species of amphibian, what form of reptiles most closely resembles the old ancestor? How did each of these ancestors look? I do not know. It looks as if our ancestral tree were entirely uncertain and we were left without any foundation for history or argument.
But the history of the development of anatomical details, however important and desirable, is not the only history which can be written, nor is it essential. It would be interesting to know the size of brain, girth of chest, average stature, and the features of the ancient Greeks and Romans. But this is not the most important part of their history, nor is it essential. The great question is, What did they contribute to human progress?
Even if we cannot accurately portray the anatomical details of a single ancestral stage, can we perhaps discover what function governed its life and was the aim of its existence? Did it live to eat, or to move, or to think? If we cannot tell exactly how it looked, can we tell what it lived for and what it contributed to the evolution of man?
Now, the sequence of dominant functions or aims in life can be traced with far more ease and safety, not to say certainty, than one of anatomical details. The latter characterize small groups, genera, families, or classes; while the dominant function characterizes all animals of a given grade, even those which through degeneration have reverted to this grade.
Even if I cannot trace the exact path which leads to the mountain-top, I may almost with certainty affirm that it leads from meadow and pasture through forest to bare rock, and thence over snow and ice to the summit; for each of these forms a zone encircling the mountain. Very similarly I find that, whatever genealogical tree I adopt, one sequence in the dominance of functions characterizes them all; digestion is dominant before locomotion and locomotion before thought.
And it is hardly less than a physiological necessity that it should be so. The plant can and does exist, living almost purely for digestion and reproduction, and the same is true of the lowest and most primitive animals. A muscular system cannot develop and do its work until some sort of a digestive system has arisen to furnish nutriment, any more than a steam-engine can run without fuel. And a brain is of no use until muscle and sense-organs have appeared.
This sequence of dominant functions,[A] of physiological dynasties, would seem therefore to be a fact. And our series of forms described in the second, third, and fourth chapters is merely a concrete illustration showing how this sequence may have been evolved. The substitution of other terms in the anatomical series there described—amoeba, volvox, etc.—would not affect this result. By a change in the form of our history we have eliminated to a large extent the sources of uncertainty and error. And the dominant function of a group throws no little light on the details of its anatomy.
[Footnote A: See condensed Chart of Development, etc., p. 309.]
If we can be satisfied that ever higher functions have risen to dominance in the successive stages of animal and human development, if we can further be convinced that the sequence is irreversible, we shall be convinced that future man will be more and more completely controlled by the very highest powers or aims to which this sequence points. Otherwise we must disbelieve the continuity of history. But the germs of the future are always concealed in the history of the present. Hence—pardon the reiteration—if we can once trace this sequence of dominant functions, whose evolution has filled past ages, we can safely foretell something at least of man's future development.
The argument and method is therefore purely historical. Here and there we will try to find why and how things had to be so. But all such digressions are of small account compared with the fact that things were or are thus and so. And a mistaken explanation will not invalidate the facts of history.
The subject of our history is the development, not of a single human race nor of the movements of a century, but the development of animal life through ages. And even if our attempts to decipher a few pages here and there in the volumes of this vast biological history are not as successful as we could hope, we must not allow ourselves to be discouraged from future efforts. Even if our translation is here and there at fault, we must never forget the existence of the history. Some of the worst errors of biologists are due to their having forgotten that in the lower stages the germs of the higher must be present, even though invisible to any microscope. Our study of the worm is inadequate and likely to mislead us, unless we remember that a worm was the ancestor of man. And a biologist who can tell us nothing about man is neglecting his fairest field.
Conversely history and social science will rest on a firmer basis when their students recognize that many human laws and institutions are heirlooms, the attainments, or direct results of attainments, of animals far below man. We are just beginning to recognize that the study of zooelogy is an essential prerequisite to, and firm foundation for, that of history, social science, philosophy, and theology, just as really as for medicine. An adequate knowledge of any history demands more than the study of its last page. The zooelogist has been remiss in not claiming his birthright, and in this respect has sadly failed to follow the path pointed out by Mr. Darwin.
For palaeontology, zooelogy, history, social and political science, and philosophy are really only parts of one great science, of biology in the widest sense, in distinction from the narrower sense in which it is now used to include zooelogy and botany. They form an organic unity in which no one part can be adequately understood without reference to the others. You know nothing of even a constellation, if you have studied only one of its stars. Much less can the study of a single organ or function give an adequate idea of the human body.
Only when we have attained a biological history can we have any satisfactory conception of environment. As we look about us in the world, environment often seems to us to be a chaos of forces aiding or destroying good and bad, fit and unfit, alike.
But our history of animal and human progress shows us successive stages, each a little higher than the preceding, and surviving, for a time at least, because more completely conformed to environment. If this be true, and it must be true unless our theory of evolution be false, higher forms are more completely conformed to their environment than lower; and man has attained the most complete conformity of all. Our biological history is therefore a record of the results of successive efforts, each attaining a little more complete conformity than the preceding. From such a history we ought to be able to draw certain valid deductions concerning the general character and laws of our environment, to discover the direction in which its forces are urging us, and how man can more completely conform to it.
If man is a product of evolution, his mental and moral, just as really as his physical, development must be the result of such a conformity. The study of environment from this standpoint should throw some light on the validity of our moral and religious creeds and theories. It would seem, therefore, not only justifiable, but imperative to attempt such a study.
Our argument is not directly concerned with modern theories of heredity, or variation, or with the "omnipotence" or secondary importance of natural selection. And yet Naegeli, and especially Weismann, have had so marked an influence on modern thought that we cannot afford to neglect their theories. We will briefly notice these in the closing chapter.
CHAPTER I
THE PROBLEM: THE MODE OF ITS SOLUTION
The story of a human life can be told in very few words. A youth of golden dreams and visions; a few years of struggle or of neglected opportunities; then retrospect and the end.
"We come like water, and like wind we go."
But how few of the visions are realized. Faust sums up the whole of life in the twice-repeated word versagen, renounce, and history tells a similar story. Terah died in Haran; Abraham obtained but a grave in the land promised him and his children; Jacob, cheated in marriage, bitterly disappointed in his children, died in exile, leaving his descendants to become slaves in the land of Egypt; and Moses, their heroic deliverer, died in the mountains of Moab in sight of the land which he was forbidden to enter. You may answer that it is no injury that the promise is too large, the vision too grand, to be fulfilled in the span of a single life, but must become the heritage of a race. But what has been the history of Abraham's descendants? A death-grapple for existence, captivity, and dispersion. Their national existence has long been lost.
Was there ever a nation of grander promise than Greece or Rome? But Greece died of premature old age, and Rome of rottenness begotten of sin. But each of them, you will say, left a priceless heritage to the immortal race. But if Greece and Rome and a host of older nations, of which History has often forgotten the very name, have failed and died, can anything but ultimate failure await the race? Is human history to prove a story told by an idiot, or does it "signify" something? Is the great march of humanity, which Carlyle so vividly depicts, "from the inane to the inane, or from God to God?"
This is the sphinx question put to every thinking man, and on his answer hangs his life. For according to that answer, he will either flinch and turn back, or expend every drop of blood and grain of power in urging on the march.
To this question the Bible gives a clear and emphatic answer. "God created man in his own image," and then, as if men might refuse to believe so astounding a statement, it is repeated, "in the image of God created he him." When, and by what mode or process, man was created we are not told. His origin is condensed almost into a line, his present and future occupy all the rest of the book. Whence we came is important only in so far as it teaches us humility and yet assures us that we may be Godlike because we are His handiwork and children, "heirs of God and joint heirs with Christ of a heavenly inheritance."
Now has Science any answer to this vital question? Perhaps. But this much is certain; it can foretell the future only from the past. Its answer to the question whither must be an inference from its knowledge as to whence we have come. The Bible looks mainly at the present and future; Science must at least begin with the study of the past. The deciphering of man's past history is the great aim of Biology, and ultimately of all Science. For the question of Man's past is only a part of a greater question, the origin of all living species.
We may say broadly that concerning the origin of species two theories, and only two, seem possible. The first theory is that every species is the result of an act of immediate creation. And every true species, however slightly it may differ from its nearest relative, represents such a creative act, and once created is practically unchangeable. This is the theory of immutability of species. According to the second theory all higher, probably all present existing, species are only mediately the result of a creative act. The first living germ, whenever and however created, was infused with power to give birth to higher species. Of these and their descendants some would continue to advance, others would degenerate. Each theory demands equally for its ultimate explanation a creative act; the second as much as, if not more than, the first. According to the first theory the creative power has been distributed over a series of acts, according to the second theory it has been concentrated in one primal creation. The second is the theory of the mutability of species, or, in general, of evolution, but not necessarily of Darwinism alone.
The first theory is considered by many the more attractive and hopeful. Now a theory need not be attractive, nor at first sight appear hopeful, provided only it is true. But let me call your attention to certain conclusions which, as it appears to me, are necessarily involved in it. Its central thought is the practical immutability of species. Each one of these lives its little span of time, for species are usually comparatively short-lived, grows possibly a very little better or worse, and dies. Its progress has added nothing to the total of life; its degeneration harmed no one, hardly even itself; it was doomed from the start. Progress there has been, in a sense. The Creator has placed ever higher forms on the globe. But all the progress lies in the gaps and distances between successive forms, not in any advance made, or victory won, by the species or individual. The most "aspiring ape," if ever there was such a being, remains but an ape. He must comfort himself with the thought that, while he and his descendants can never gain an inch, the gap between himself and the next higher form shall be far greater than that between himself and the lowest monkey.
And if this has been the history of thousands of other species, why should it not be true of man also? Who can wonder that many who accept this theory doubt whether the world is growing any better, or whether even man will ever be higher and better than he now is? Would it not be contrary to the whole course of past history, if you can properly call such a record a history, if he could advance at all? Now I have no wish to misrepresent this or any honestly accepted theory, but it appears to me essentially hopeless, a record not of the progress of life on the globe, but of a succession of stagnations, of deaths. I can never understand why some very good and intelligent people still think that the theory of the immediate creation of each species does more honor to the Creator and his creation than the theory of evolution. Evolution is a process, not a force. The power of the Creator is equally demanded in both cases; only it is differently distributed. And evolution is the very highest proof of the wisdom and skill of the Creator. It elevates our views of the living beings, must it not give a higher conception of Him who formed them?
The plant in its first stages shows no trace of flowers, but of leaves only. Later a branch or twig, similar in structure to all the rest, shortens. The cells and tissues which in other twigs turn into green leaves here become the petals and other organs of the rose or violet. Let us suppose for a moment that every rose and violet required a special act of immediate creation, would the springtime be as wonderful as now? Would the rose or violet be any more beautiful, or are they any less flowers because developed out of that which might have remained a common branch? The plant at least is glorified by the power to give rise to such beauty. And is not the creation of the seed of a violet or rose something infinitely grander than the decking of a flowerless plant with newly created roses? The attainment of the highest and most diversified beauty and utility with the fewest and simplest means is always the sign of what we call in man "creative" genius. Is not the same true of God? I think you all feel the force of the argument here.
There were at one time no flowering plants. The time came at last for their appearance. Which is the higher, grander mode of producing them, immediate creation of every flowering species, or development of the flower out of the green leaves of some old club moss or similar form? The latter seems to me at least by far the higher mode. And to have created a ground-pine which could give rise to a rose seems far more difficult and greater than to have created both separately. It requires more genius, so to speak. It gives us a far higher opinion of the ground-pine; does it disgrace the rose? We can look dispassionately at plants. The rose is still and always a rose, and the oak an oak, whatever its origin. And I believe that we shall all readily admit that evolution is here a theory which does the highest honor to the wisdom and power of the Creator. What if the animal kingdom is continually blossoming in ever higher forms? Does not the same reasoning hold true, only with added force? I firmly believe that we should all unhesitatingly answer, yes, could we but be assured that all men would everywhere and always believe that we, men, were the results of an immediate creative act.
But why do we so strenuously object to the application to ourselves of the theory of evolution? One or two reasons are easily seen. We have all of us a great deal of innate snobbery, we would rather have been born great than to have won greatness by the most heroic struggle. But is man any less a man for having arisen from something lower, and being in a fair way to become something higher? Certainly not, unless I am less a man for having once been a baby. It is only when I am unusually cross and irritable that I object to being reminded of my infancy. But a young child does not like to be reminded of it. He is afraid that some one will take him for a baby still. And the snob is always desperately afraid that some one will fail to notice what a high-born gentleman he is.
Now man can relapse into something lower than a brute; the only genuine brute is a degenerate man. And we all recognize the strength of tendencies urging us downward. Is not this the often unrecognized kern of our eagerness for some mark or stamp that shall prove to all that we are no apes, but men? It is not the pure gold that needs the "guinea stamp." If we are men, and as we become men, we shall cease to fear the theory of evolution. Now this is not the only, or perhaps the greatest, objection which men feel or speak against the theory. But I must believe that it has more weight with us than we are willing to admit.
But some say that the theory of immediate creation and immutability of species is the more natural and has always been accepted, while the theory of evolution is new and very likely to be as short-lived as many another theory which has for a time fascinated men only to be forgotten or ridiculed.
But the idea of evolution is as old as Hindu philosophy. The old Ionic natural philosophers were all evolutionists. So Aristophanes, quoting from these or Hesiod concerning the origin of things, says: "Chaos was and Night, and Erebus black, and wide Tartarus. No earth, nor air nor sky was yet; when, in the vast bosom of Erebus (or chaotic darkness) winged Night brought forth first of all the egg, from which in after revolving periods sprang Eros (Love) the much desired, glittering with golden wings; and Eros again, in union with Chaos, produced the brood of the human race." Here the formative process is a birth, not a creation; it is evolution pure and simple. "According to the ancient view," says Professor Lewis, "the present world was a growth; it was born, it came from something antecedent, not merely as a cause but as its seed, embryo or principium. Plato's world was a 'zoon,' a living thing, a natural production."
Furthermore, to the ancient writers of the Bible the idea of origin by birth from some antecedent form—and this is the essential idea of evolution—was perfectly natural. They speak of the "generations of the heavens and the earth" as of the "generations" of the patriarchs. The first book of the Bible is still called Genesis, the book of births. The writer of the ninetieth Psalm says, "Before the mountains were born, or ever thou hadst brought to birth the earth and the world." And what satisfactory meaning can you give to the words, "Let the earth bring forth," and "the earth brought forth," in immediate proximity to the words, "and God made," unless while the ultimate source was God's creative power, the immediate process of formation was one of evolution.
The Bible is big and broad enough to include both ideas, the human mind is prone to overestimate the one or the other. Traces, at least, of a similar mode of thought persisted by the Greek Fathers of the Church, and disappeared, if ever, with the predominance of Latin theology. To the oriental the idea of evolution is natural. The earth is to him no inert, resistant clod; she brings forth of herself.
But our ancestors lived on a barren soil beneath a forbidding sky. They were frozen in winter and parched in summer. Nature was to them no kind foster-mother, but a cruel stepmother, training them by stern discipline to battle with her and the world. They peopled the earth with gnomes and cobolds and giants, and their nymphs were the Valkyre. Their God was Thor, of the thunderbolt and hammer, and who yet lived in continual dread of the hostile powers of Nature. A Norse prophet or prophetess standing beside Elijah at Horeb would have bowed down before the earthquake or the fire; the oriental waited for the "still small voice." And we are heirs to a Latin theology grafted on to the Thor-worship of our pagan ancestors. The idea of a Nature producing beneficently and kindly at the word of a loving God is foreign to all our inherited modes of thought. And our views of the heart of Nature are about as correct as those of our ancestors were of God. A little more of oriental tendencies of thought would harm neither our theology nor our life.
What, then, is the biblical idea of Nature? God speaks to the earth, in the first chapter of Genesis, and the earth responds by "giving birth" to mountains and living beings. It is evidently no mere lifeless, inert clod, but pulsating with life and responsive to the divine commands. While yet a chaos it had been brooded over by the Divine Spirit. It is like the great "wheels within wheels," with rings full of eyes round about, which Ezekiel saw in his vision by the river Chebar. "When the living creatures went, the wheels went by them; and when the living creatures were lifted up from the earth, the wheels were lifted up. Whithersoever the spirit was to go, they went, thither was their spirit to go; and the wheels were lifted up over against them: for the spirit of the living creatures (or of life) was in the wheels." And above the living creatures was the firmament and the throne of God. So Nature may be material, but it is material interpenetrated by the divine; if you call it a fabric, the woof may be material but the warp is God. This view contains all the truth of materialism and pantheism, and vastly more than they, and it avoids their errors and omissions.
To the old metaphysical hypothesis of evolution Mr. Darwin gave a scientific basis. It had always been admitted that species were capable of slight variation and that this divergence might become hereditary and thus perhaps give rise to a variety of the parent species. But it was denied that the variation could go on increasing indefinitely, it seemed soon to reach a limit and stop. Early in the present century Lamarck had attempted to prove that by the use and disuse of organs through a series of generations a great divergence might arise resulting in new species. But the theory was crude, capable at best of but limited application, and fell before the arguments and authority of Cuvier. The times were not ripe for such a theory. Some fifty years later, Mr. Darwin called attention to the struggle for existence as a means of aggregating these slight modifications in a divergence sufficient to produce new species, genera, or families. His argument may be very briefly stated as follows:
1. There is in Nature a law of heredity; like begets like.
2. The offspring is never exactly like the parent; and the members of the second generation differ more or less from one another. This is especially noticeable in domesticated plants and animals, but no less true of wild forms. If the parent is not exactly like the other members of the species, some of its descendants will inherit its peculiarities enhanced, others diminished.
3. Every species tends to increase in geometrical progression. But most species actually increase in number very slowly, if at all. Now and then some insect or weed escapes from its enemies, comes under favorable food conditions, and multiplies with such rapidity that it threatens to ravage the country. But as it multiplies it furnishes an abundance of food for the enemies which devour it, or of food and place for the parasites in and upon it; and they increase with at least equal rapidity. Hence while the vanguard increases prodigiously in numbers, because it has outrun these enemies, the rear is continually slaughtered. And thus these plagues seem in successive generations to march across the continent.
And yet even they give but a faint idea of the reproductive powers of plants and animals. The female fish produces often many thousands, sometimes hundreds of thousands of eggs. Insects generally from a hundred to a thousand. Even birds, slowly as they increase, produce in a lifetime probably at least from twelve to twenty eggs. Now let us suppose that all these eggs developed, and all the birds lived out their normal period of life, and reproduced at the same rate. After not many centuries there would not be standing room on the globe for the descendants of a single pair.
Again, of the one hundred eggs of an insect let us suppose that only sixty develop into the first larval, caterpillar, stage. Of these sixty, the number of members of the species remaining constant, only two will survive. The other fifty-eight die—of starvation, parasites, or other enemies, or from inclement weather. Now which two of all shall survive? Those naturally best able to escape their enemies or to resist unfavorable influences; in a word, those best suited to their conditions, or, to use Mr. Darwin's words, "conformed to their environment."
Now if any individual has varied so as to possess some peculiarity which enables it even in slight degree to better escape its enemies or to resist unfavorable conditions, those of its descendants who inherit most markedly this peculiar quality or variation will be the most likely to escape, those without it to perish. If a form varies unfavorably, becomes for instance more conspicuous to its enemies, it will almost certainly perish. Thus favorable variations tend to increase and become more marked from generation to generation.
Now it has always been known that breeders could produce a race of markedly peculiar form or characteristics by selecting the individuals possessing this quality in the highest degree and breeding only from these. The breeder depends upon heredity, variation, and his selection of the individuals from which to breed. Similarly in nature new species have arisen through heredity, variation, and a selection according to the laws of nature of those varying in conformity with their environment. And this Mr. Darwin called natural, in contrast with the breeder's artificial, "selection," arising from the "struggle for existence," and resulting in what Mr. Spencer has called the "survival of the fittest."
Let us take a single illustration. Many of the species of beetles on oceanic islands have very rudimentary wings, or none at all, and yet their nearest relatives are winged forms on some neighboring continent. Mr. Darwin would explain the origin of these evidently distinct wingless species as follows: They are descended from winged ancestors blown or otherwise transported thither from the neighboring continent. But beetles are slow and clumsy fliers, and on these wind-swept islands those which flew most would be blown out to sea and drowned. Those which flew the least, and these would include the individuals with more poorly developed wings, would survive. There would thus be a survival in every generation of a larger proportion of those having the poorest wings, and destruction of those whose wings were strong, or whose habits most active. We have here a natural selection which must in time produce a species with rudimentary or aborted wings, just as surely as a human breeder, by artificial selection can produce such an animal as a pug or a poodle. These, like sin, are a human device; nature should not be held responsible for them.
But you may urge that the variation which would take place in a single generation would be, as a rule, too slight to be of any practical value to the animal, and could not be fostered by natural selection until greatly enhanced by some other means. Let us think a moment. If ten ordinary men run in a foot-race, the two foremost may lead by several feet. But if the number of runners be continually increased the finish will be ever closer until finally but an atom more wind or muscle or pluck would make all the difference between winning and losing the prize.
Similarly the million or more young of any species of insect in a given area may be said to run a race of which the prize is life, and the losing of which means literally death. The competition is inconceivably severe. How indefinitely slight will be the difference between the poorest of the 2,000 or 20,000 survivors and the best of the more than 900,000 which perish. The very slightest favorable variation may make all the difference between life and sure death. And yet these indefinitely slight variations continued and aggregated through ages would foot up an immense total divergence. The chalk cliffs of England have been built up of microscopic shells.
I have tried to give you very briefly a sketch of the essential points of Mr. Darwin's theory of evolution. But you should all read that marvel of patience, industry, clear insight, close reasoning, and grand honesty, the "Origin of Species." I have no time to give the arguments in its favor or to attempt to meet the objections which may arise in your minds. I ask you to believe only this much; that the theory is accepted with practical unanimity by scientific men because it, and it alone, furnishes an explanation for the facts which they discover in their daily work. And this is the strongest proof of the truth of any accepted theory.
Inasmuch as it is accepted by all scientists and largely by the public, it is certainly worth your while to know whether it has any bearing on the great moral and religious questions which you are considering. And in these lectures I shall take for granted, what some scientists still doubt, that man also is a product of evolution. For the weight of evidence in favor of this view is constantly increasing, and seems already to strongly preponderate. Also I wish in these lectures to grant all that the most ardent evolutionist can possibly claim. Not that I would lower man's position, but I have a continually increasing respect for the so-called "lower animals."
Now if the theory of evolution be true, and really only on this condition, life has had a history; and human history began ages before man's actual appearance on the globe, just as American history began to be fashioned by Anglo-Saxons, Danes, and Normans before they set foot even in England. We study history mainly to deduce its laws; and that knowing them we may from the past forecast the future, prepare for its emergencies, and avoid or wisely meet, its dangers. And we rely on these laws of history because they are the embodiment of ages of human experience.
Whatever be our system of philosophy we all practically rely on past experience and observation. Fire burns and water drowns. This we know, and this knowledge governs our daily lives, whatever be our theories, or even our ignorance, of the laws of heat and respiration. Now human history is the embodiment of the experience of the race; and we study it in the full confidence that, if we can deduce its laws, we can rely on racial experience certainly as safely as on that of the individual. Furthermore, if we can discover certain great movements or currents of human action or progress moving steadily on through past centuries, we have full confidence that these movements will continue in the future. The study of history should make us seers.
But the line of human progress is like a mountain road, veering and twisting, and often appearing to turn back upon itself, and having many by-roads, which lead us astray. If we know but a few miles of it we cannot tell whether it leads north or south or due west. But if from any mountain-top we can gain a clear bird's-eye view of its whole course, we easily distinguish the main road, its turns become quite insignificant, we see that it leads as directly as any engineering skill could locate it through the mountains to the fertile plains and rich harvests beyond.
Now our knowledge of the history of man covers so brief a period that we can scarcely more than hazard a guess as to the trend of human progress. Many of the most promising social movements are like by-roads which, at first less steep and difficult, end sooner or later against impassable obstacles. And even if there be a main line of march, advance seems to alternate with retreat, progress with retrogression. To illustrate further, the great waves rush onward only to fall back again, and we can hardly tell whether the tide is flowing or ebbing.
Yet already certain tendencies appear fairly clear. Governments tend to become democratic, if we define democracy as "any form of government in which the will of the people finds sovereign expression." The tendency of society seems to be toward furnishing all its members equality of opportunity to make the most of their natural endowments. But if we are convinced that these statements express even vaguely the tendency of human development in all its past history, we are confident that these tendencies will continue in the future for a period somewhat proportional to their time of growth in the past. If we are wise, we try to make our own lives and actions, and those of our fellows, conform to and advance them. Otherwise our lives will be thrown away.
But if the theory of evolution be true, human history is only the last page of the one history of all life. If we are to gain any adequate, true, extensive view of human progress, we must read more than this. We must take into account the history of man when he was not yet man. And if we believe in the future continuance of tendencies of a few centuries' growth, we shall rest assured of the permanence of tendencies which have grown and strengthened through the ages.
Our confidence in the results of historical study is therefore proportioned to the extent and thoroughness of the experience which they record, and to the time during which these laws can be proven to have held good. If I can make it even fairly probable that these laws, on obedience to which human progress and success seem to depend, are merely quoted from a grander code applicable to all life in all times, your confidence in them will be even greater. I trust I can prove to you that the animal kingdom has not drifted aimlessly at the mercy of every wind and tide and current of circumstance. I hope to show that along one line it has from the beginning through the ages held a steady course straight onward, and that deviation from this course has always led to failure or degeneration. From so vast a history we may hope to deduce some of the great laws of true success in life. Furthermore, if along this central line, at the head of which man stands, there always has been progress, we cannot doubt that future progress will be as certain, and perhaps far more rapid. In all the struggle of life we shall have the sure hope of success and victory; if not for ourselves still for those who shall come after us. "We are saved by hope." And we may be confident that this hope will never make us ashamed.
Finally, even from our present knowledge of the past progress of life we shall hope to catch hints at least that man's only path to his destined goal is the straight and narrow road pointed out in the Bible. If in this we are even fairly successful we shall find a relation and bond between the Bible and Science worthy of all consideration. And this is the only agreement which can ever satisfy us.
If I wished to bring before you a view of the development of man, I should best choose individuals or families from various periods of human history from the earliest times down to the present. I should try to tell you how they looked and lived. But if anyone should attempt to condense into three lectures such a history of even one line of the human race, you would probably think him insane. Even if he succeeded in giving a fairly clear view of the different stages, the successive stages would be so remote from one another, such vast changes would necessarily remain unnoticed or unexplained that you would hardly believe that they could have any genetic relation or belong to one developmental series.
But the history which I must attempt to condense for you is measured by ages, and the successive terms of the series will be indefinitely more remote from each other than the life and thoughts of Lincoln or Washington from those of our most primitive Aryan ancestor or of the rudest savage of the Stone Age. The series must appear exceedingly disconnected. Systems of organs will apparently spring suddenly into existence, and we shall have no time to trace their origin or earlier development. Even if we had an abundance of time many gaps would still remain; for the forms, which according to our theory must have occupied their place, have long since disappeared and left no trace nor sign. We have generally no conception at all of the amount of extermination and degeneration which have taken place in past ages.
I grant frankly that I do not believe that the forms which I have selected represent exactly the ancestors of man. They have all been more or less modified. I claim only that in the balance and relative development of their organic systems—muscular, digestive, nervous, etc.—they give us a very fair idea of what our ancestor at each stage must have been. But it is on this balance and relative development of the different systems, that is, whether an animal is more reproductive, digestive, or nervous, that my argument will in the main be based.
But if the older ancestors have so generally disappeared, and their surviving relatives have been so greatly modified, how can we make even a shrewd guess at the ancestry of higher forms? The genealogy of the animal kingdom has been really the study of centuries, although the earlier zooelogists did not know that this was to be the result of their labors. The first work of the naturalist was necessarily to classify the plants and animals which he found, and catalogue and tabulate them so that they might be easily recognized, and that later discovered forms might readily find a place in the system. Hypotheses and theories were looked upon with suspicion. "Even Linnaeus," says Romanes, "was express in his limitations of true scientific work in natural history to the collecting and arranging of species of plants and animals." The question, "What is it?" came first; then, "How did it come to be what it is?" We are just awakening to the question, "Why this progressive system of forms, and what does it all mean?"
Let us experiment a little in forming our own classification of a few vertebrates. We see a bat flying through the air. We mistake it for a bird. But a glance at it shows that it is a mammal. It is covered with hair. It has fore and hind legs. Its wings are membranes stretched between the fingers and along the sides of the body. It has teeth. It suckles its young. In all these respects it differs from birds. It differs from mammals only in its wings. But we remember that flying squirrels have a membrane stretching along the sides of the body and serving as a parachute, though not as wings. We naturally consider the wings as a sort of after-thought superinduced on the mammalian structure. We do not hesitate to call it a mammal.
The whale makes us more trouble; it certainly looks remarkably like a fish. But the fin of its tail is horizontal, not vertical. Its front flippers differ altogether from the corresponding fins of fish; their bones are the same as those occurring in the forelegs of mammals, only shorter and more crowded together. Later we find that it has lungs, and a heart with four chambers instead of only two, as in fish. The vertebrae of its backbone are not biconcave, but flat in front and behind. And, finally, we discover that it suckles its young. It, too, is in all its deep-seated characteristics a mammal. It is fish-like only in characteristics which it might easily have acquired in adaptation to its aquatic life. And there are other aquatic mammals, like the seals, in which these characteristics are much less marked. Their adaptation has evidently not gone so far.
Now the first attempts resulted in artificial classifications, much like our grouping of bats with birds and whales with fish. All animals, like coral animals and starfishes, whose similar parts were arranged in lines radiating from a centre, were united as radiates, however much they might differ in internal structure and grade of organization. But this radiate structure proved again to be largely a matter of adaptation.
Practically all animals having a heavy calcareous shell were grouped with the snails and oysters as mollusks. But the barnacle did not fit well with other mollusks. Its shell was entirely different. It had several pairs of legs; and no mollusk has legs. The barnacle is evidently a sessile crab or better crustacean. Its molluscan characteristics were only skin-deep, evidently an adaptation to a mode of life like that of mollusks. The old artificial systems were based too much on merely external characteristics, the results of adaptation. When the internal anatomy had been thoroughly studied their groups had to be rearranged.
Reptiles and amphibia were at first united in one class because of their resemblance in external form. Our common salamanders look so much like lizards that they generally pass by this name. But the young salamander, like all amphibia, breathes by gills, its skeleton differs greatly from, and is far weaker than, that of the lizard, and there are important differences in the circulatory and other systems. Moreover, practically all amphibia differ from all reptiles in these respects. Evidently the fact that the alligator and many snakes and turtles (of which neither the young nor the embryos ever breathe by gills) live almost entirely in the water, is no better reason for classifying these with amphibia than to call a whale a fish, and not a mammal, because of its form and aquatic life.
When the comparative anatomy of fish, amphibia, and reptiles had been carefully studied it was evident that the amphibia stood far nearer the fish in general structure, while the higher reptiles closely approached birds. Then it was noticed that our common fish formed a fairly well-defined group, but that the ganoids, including the sturgeons, gar-pikes, and some others, had at least traces of amphibian characteristics. Such generalized forms, with the characteristics of the class less sharply marked, were usually by common consent placed at the bottom of the class. And this suited well their general structure, while in particular characteristics they were often more highly organized than higher groups of the same class.
The palaeontologist found that the oldest fossil forms belonged to these generalized groups, and that more highly specialized forms—that is, those in which the special class distinctions were more sharply and universally marked—were of later geological origin. Thus the oldest fish were most like our present ganoids and sharks, though differing much from both. Our common teleost fish, like perch and cod, appeared much later. The oldest bird, the archaeopteryx, had a long tail like that of a lizard, and teeth; and thus stood in many respects almost midway between birds and reptiles. And most of the earliest forms were "comprehensive," uniting the characteristics of two or more later groups. Thus as the classification became more natural, based on a careful comparison of the whole anatomy of the animals, its order was found to coincide in general with that of geological succession.
Then the zooelogist began to ask and investigate how the animal grew in the egg and attained its definite form. And this study of embryology brought to light many new and interesting facts. Agassiz especially emphasized and maintained the universality of the fact that there was a remarkable parallelism between embryos of later forms and adults of old or fossil groups. The embryos of higher forms, he said, pass through and beyond certain stages of structure, which are permanent in lower and older members of the same group.
You remember that the fin on the tail of a fish is as a rule bilobed. Now the backbone of a perch or cod ends at a point in the end of the tail opposite the angle between the two lobes, without extending out into either of them. In the shark it extends almost to the end of the upper lobe. Now we have seen that sharks and ganoids are older than cod. In the embryo of the cod or perch the backbone has, at an early stage, the same position as in the shark or ganoid; only at a later stage does it attain its definite position.
So Agassiz says the young lepidosteus (a ganoid fish), long after it is hatched, exhibits in the form of its tail characters thus far known only among the fossil fishes of the Devonian period. The embryology of turtles throws light upon the fossil chelonians. It is already known that the embryonic changes of frogs and toads coincide with what is known of their succession in past ages. The characteristics of extinct genera of mammals exhibit everywhere indications that their living representatives in early life resemble them more than they do their own parents. A minute comparison of a young elephant with any mastodon will show this most fully, not only in the peculiarities of their teeth, but even in the proportion of their limbs, their toes, etc. It may therefore be considered as a general fact that the phases of development of all living animals correspond to the order of succession of their extinct representatives in past geological times. The above statements are quoted almost word for word from Professor Agassiz's "Essay on Classification." The larvae of barnacles and other more degraded parasitic crustacea are almost exactly like those of Crustacea in general. The embryos of birds have a long tail containing almost or quite as many vertebrae as that of archaeopteryx. But most of these never reach their full development but are absorbed into the pelvis, or into the "ploughshare" bone supporting the tail feathers. Thus older forms may be said to have retained throughout life a condition only embryonic in their higher relatives. And the natural classification gave the order not only of geological succession but also of stages of embryonic development. Thus the system of classification improved continually, although more and more intermediate forms, like archaeopteryx, were discovered, and certain aberrant groups could find no permanent resting-place.
But why should the generalized comprehensive forms stand at the bottom rather than the top of the systematic arrangement of their classes? Why should the system of classification coincide with the order of geologic occurrence, and this with the series of embryonic stages? Above all, why should the embryos of bird and perch form their tails by such a roundabout method? Why should the embryo of the bird have the tail of a lizard? No one could give any satisfactory explanation, although the facts were undoubted.
Mr. Darwin's theory was the one impulse needed to crystallize these disconnected facts into one comprehensible whole. The connecting link was everywhere common descent, difference was due to the continual variation and divergence of their ancestors. The classification, which all were seeking, was really the ancestral tree of the animal kingdom. Forms more generalized should be placed lower down on the ancestral tree, and must have had an earlier geological occurrence because they represented more nearly the ancestors of the higher. But this explains also the facts of embryonic development.
According to Mr. Darwin's theory all the species of higher animals have developed from unicellular ancestors. It had long been known that all higher forms start in life as single cells, egg and spermatozoon. And these, fused in the process of fertilization, form still a single cell. And when this single cell proceeds through successive embryonic stages to develop into an adult individual it naturally, through force of hereditary habit, so to speak, treads the same path which its ancestors followed from the unicellular condition to their present point of development. Thus higher forms should be expected to show traces of their early ancestry in their embryonic life. Older and lower adult forms should represent persistent embryonic stages of higher. It could not well be otherwise.
But the path which the embryo has to follow from the egg to the adult form is continually lengthening as life advances ever higher. From egg to sponge is, comparatively speaking, but a step; it is a long march from the egg to the earthworm; and the vertebrate embryo makes a vast journey. But embryonic life is and must remain short. Hence in higher forms the ancestral stages will often be slurred over and very incompletely represented. And the embryo may, and often does, shorten the path by "short-cuts" impossible to its original ancestor. Still it will in general hold true, and may be recognized as a law of vast importance, that any individual during his embryonic life repeats very briefly the different stages through which his ancestors have passed in their development since the beginning of life. Or, briefly stated, ontogenesis, or the embryonic development of the individual, is a brief recapitulation of phylogenesis, or the ancestral development of the phylum or group.
The illustration and proof of this law is the work of the embryologist. We have time to draw only one or two illustrations from the embryonic development of birds. We have already seen that the embryonic bird has the long tail of his reptilian ancestor. In early embryonic life it has gill-slits leading from the pharynx to the outside of the neck like those through which the water passes in the respiration of fish. The Eustachian tube and the canal of the external ear of man, separated only by the "drum," are nothing but such an old persistent gill-slit. No gills ever develop in these, but the great arteries run to them, and indeed to all parts of the embryo, on almost precisely the same general plan as in the adult fish. Only later is the definite avian circulation gradually acquired.
This law is even more strikingly illustrated in the embryonic development of the vertebral column and skull, if we had time to trace their development. And the development of the excretory system points to an ancestor far more primitive than even the fish. Our embryonic development is one of the very strongest evidences of our lowly origin.
Thus we have three sources of information for the study of animal genealogy. First, the comparative anatomy of all the different groups of animals; second, their comparative embryology; and third, their palaeontological history. Each source has its difficulties or defects. But taken all together they give us a genealogical tree which is in the main points correct, though here and there very defective and doubtful in detail. The points in which we are left most in doubt in regard to each ancestor are its modes of life and locomotion, and body form. But these may temporarily vary considerably without affecting to any great extent the general plan of structure and the line of development of the most important deep-seated organs.
I have chosen a line composed of forms taken from the comparative anatomical series. All such present existing forms have probably been modified during the lapse of ages. But I shall try to tell you when they have diverged noticeably from the structure of the primitive ancestor of the corresponding stage. It is much safer for us to study concrete, actual forms than imaginary ones, however real may have been the former existence of the latter. And, after all, their lateral divergence is of small account compared with the great upward and onward march of life, to the right and left of which they have remained stationary or retrograded somewhat, like the tribes which remained on the other side of Jordan and never entered the Promised Land.
To recapitulate: Our question is the Whence and the Whither of man. To this question the Bible gives a clear and definite answer. Can Science also give an answer, and is this in the main in accord with the answer of Scripture? Science can answer the question only by the historical method of tracing the history of life in the past and observing the goal toward which it tends. If the evolution theory be true, the record of human achievement and progress forms only one short chapter in the history of the ages. If from the records of man's little span of life on the globe we can deduce laws of history on whose truth we can rely, with how much greater confidence and certainty may we rely on laws which have governed all life since its earliest appearance?—always provided that such can be found.
Our first effort must therefore be to trace the great line of development through a few of its most characteristic stages from the simplest living beings up to man. This will be our work in the three succeeding lectures. And to these I must ask you to bring a large store of patience. Anatomical details are at best dry and uninteresting. But these dry facts of anatomy form the foundation on which all our arguments and hopes must rest.
But if you will think long and carefully even of anatomical facts, you will see in and behind them something more and grander than they. You will catch glimpses of the divinity of Nature. Most of us travel threescore years and ten stone-blind in a world of marvellous beauty. Why does the artist see so much more in every fence-corner and on every hill-side than we, set face to face with the grandest landscapes? Primarily, I believe, because he is sympathetic, and looks on Nature as a comrade as near and dear as any human sister and companion. As Professor Huxley has said, "they get on rarely together." She speaks to the artist; to us she is dumb, and ought to be, for we are boorishly careless of her and her teachings.
Nature, to be known, must be loved. And though you have all the knowledge of a von Humboldt, and do not love her, you will never understand her or her teachings. You will go through life with her, and yet parted from her as by an adamantine wall.
I do not suppose that the author of the book of Job had ever studied geology, or mineralogy, or biology, but read him, and see whether this old prince of scientific heroes had loved, and understood, and caught the spirit of Nature. And what a grand, free spirit it was, and what a giant it made of him. I do not believe that Paul ever had a special course of anatomy or botany. But if he had not pondered long and lovingly on the structure of his body, and the germination of the seed, he never could have written the twelfth and fifteenth chapters of the first letter to the Corinthians. And time fails to speak of David and all the writers of the Psalms, and of those heroic souls misnamed the "Minor" Prophets.
Study the teachings of our Lord. How he must have considered the lilies of the field, and that such a tiny seed as that of the mustard could have produced so great an herb, and noticed and thought on the thorns and the tares and the wheat, and watched the sparrows, and pondered and wondered how the birds were fed. All his teaching was drawn from Nature. And all the study in the world could never have taught him what he knew, if it had not been a loving and appreciative study.
There is one strange and interesting passage in John's Gospel, xv. 1: "I am the true vine." My father used to tell us that the Greek word [Greek: alethine], rendered true, is usually employed of the genuine in distinction from the counterfeit, the reality in distinction from the shadow and image. Is not this perhaps the clew to our Lord's use of natural imagery? Nature was always the presentation to his senses of the divine thought and purpose. He studied the words of the ancient Scripture, he found the same words and teachings clearly and concretely embodied in the processes of Nature. The interpretation of the Parable of the Sower was no mere play of fancy to him; it was the genuine and fundamental truth, deeper and more real than the existence of the sower, the soil, and the seed. The spiritual truth was the substance; the tangible soil and seed really only the shadow. And thus all Nature was to him divine.
We all of us need to offer the prayer of the blind man, "Lord, that our eyes may be opened." Let us learn, too, from the old heathen giant, Antaeus, who, after every defeat and fall, rose strengthened and vivified from contact with his mother Earth. You will experience in life many a desperate struggle, many a hard fall. There is at such times nothing in the world so strengthening, healing, and life-giving as the thoughts and encouragements which Nature pours into the hearts and minds of her loving disciples. She will set you on your feet again, infused with new life, filled with an unconquerable spirit, with unfaltering courage, and an iron will to fight once more and win. In every battle her inspiring words will ring in your ears, and she will never fail you. We may not see her deepest realities, her rarest treasures of thought and wisdom; but if we will listen lovingly for her voice, we may be assured that she will speak to us many a word of cheer and encouragement, of warning and exhortation. For, to paraphrase the language of the nineteenth Psalm, "She has no speech nor language, her voice is not heard. But her rule is gone out throughout all the earth, and her words to the end of the world."
CHAPTER II
PROTOZOA TO WORMS: CELLS, TISSUES, AND ORGANS
The first and lowest form in our ancestral series is the amoeba, a little fresh-water animal from 1/500 to 1/1000 of an inch in diameter. Under the microscope it looks like a little drop of mucilage. This semifluid, mucilaginous substance is the Protoplasm. Its outer portion is clear and transparent, its inner more granular. In the inner portion is a little spheroidal body, the nucleus. This is certainly of great importance in the life of the animal; but just what it does, or what is its relation to the surrounding protoplasm we do not yet know. There is also a little cavity around which the protoplasm has drawn back, and on which it will soon close in again, so that it pulsates like a heart. It is continually taking in water from the body, or the outside, and driving it out again, and thus aids in respiration and excretion. The animal has no organs in the proper sense of the word, and yet it has the rudiments of all the functions which we possess.
A little projection of the outer, clearer layer of protoplasm, a pseudopodium, appears; into this the whole animal may flow and thus advance a step, or the projection may be withdrawn. And this power of change of form is a lower grade of the contractility of our muscular cells. Prick it with a needle and it contracts. It recognizes its food even at a microscopic distance; it appears therefore to feel and perceive. Perhaps we might say that it has a mind and will of its own. It is safer to say that it is irritable, that is, it reacts to stimuli too feeble to be regarded as the cause of its reaction. It engulfs microscopic plants, and digests them in the internal protoplasm by the aid of an acid secretion. It breathes oxygen, and excretes carbonic acid and urea, through its whole body surface. Its mode of gaining the energy which it manifests is therefore apparently like our own, by combustion of food material.
It grows and reaches a certain size, then constricts itself in the middle and divides into two. The old amoeba has divided into two young ones, and there is no parent left to die, and death, except by violence, does not occur. But this absence of death in other rather distant relatives of the amoeba, and probably in the amoeba itself, holds true only provided that, after a series of self-divisions, reproduction takes place after another mode. Two rather small and weak individuals fuse together in one animal of renewed vigor, which soon divides into two larger and stronger descendants. We have here evidently a process corresponding to the fertilization of the egg in higher animals; yet there is no egg, spermatozoon, or sex.
It is a little mass of protoplasm containing a nucleus, and corresponds, therefore, to one of the cells, most closely to the egg-cell or spermatozoon of higher animals. If every living being is descended from a single cell, the fertilized egg, it is not hard to believe that all higher animals are descended from an ancestor having the general structure or lack of structure of the amoeba.
But is the amoeba really structureless? Probably it has an exceedingly complex structure, but our microscopes and technique are still too imperfect to show more than traces of it. Says Hertwig: "Protoplasm is not a single chemical substance, however complicated, but a mixture of many substances, which we must picture to ourselves as finest particles united in a wonderfully complicated structure." Truly protoplasm is, to borrow Mephistopheles' expression concerning blood, a "quite peculiar juice." And the complexity of the nucleus is far more evident than that of the protoplasm. Is protoplasm itself the result of a long development? If so, out of what and how did it develop? We cannot even guess. But the beginning of life may, apparently must, have been indefinitely farther back than the simplest now existing form. The study of the amoeba cannot fail to raise a host of questions in the mind of any thoughtful man.
As we have here the animal reduced, so to speak, to lowest terms, it may be well to examine a little more closely into its physiology and compare it briefly with our own.
The amoeba eats food as we do, but the food is digested directly in the internal protoplasm instead of in a stomach; and once digested it diffuses to all parts of the cell; here it is built up into compounds of a more complex structure, and forms an integral part of the animal body. The dead food particle has been transformed into living protoplasm, the continually repeated miracle of life. But it does not remain long in this condition. In contact with the oxygen from the air it is soon oxidized, burned up to furnish the energy necessary for the motion and irritability of the body. We are all of us low-temperature engines. The digestive function exists in all animals merely to bring the food into a soluble, diffusible form, so that it can pass to all parts of the body and be used for fuel or growth. In our body a circulatory system is necessary to carry food and oxygen to the cells and to remove their waste. For most of our cells lie at a distance from the stomach, lungs, and kidney. But in a small animal the circulatory system is often unnecessary and fails. Breathing and excretion take place through the whole surface of the body. The body of the frog is devoid of scales, so that the blood is separated from the surrounding water only by a thin membrane, and it breathes and excretes to a certain extent in the same way.
But another factor has to be considered. If we double each dimension of our amoeba, we shall increase its surface four times, its mass eight-fold. Now the power of absorbing oxygen and excreting waste is evidently proportional to the excretory and respiratory surface, and much the same is true of digestion. But the amount of oxygen required, and of waste to be removed is proportional to the mass; for every particle of protoplasm requires food and oxygen, and produces waste. The particles of protoplasm in our new, larger amoeba can therefore receive only half as much oxygen as before, and rid themselves of their waste only half as fast. There is danger of what in our bodies would be called suffocation and blood-poisoning. The amoeba having attained a certain size meets this emergency by dividing into two small individuals, the division is a physical adaptation. But the many-celled animal cannot do this; it must keep its cells together. It gains the additional surface by folding and plaiting. And the complicated internal structure of higher animals is in its last analysis such a folding and plaiting in order to maintain the proper ratio between the exposed surface of the cells and their mass. And each cell in our bodies lives in one sense its own individual life, only bathed in the lymph and receiving from it its food and oxygen instead of taking it from the water.
But in another sense the cells of our body live an entirely different life, for they form a community. Division of labor has taken place between them, they are interdependent, correlated with one another, subject therefore to the laws of the whole community or organism. There are many respects in which it is impossible to compare Robinson Crusoe with a workman in a huge watch factory; yet they are both men.
Both the amoeba and we live in the closest relation to our environment, and conformity to it is evidently necessary: life has been defined as the adjustment of internal relations to external conditions. We continually take food, use it for energy and growth, and return the simpler waste compounds. We are all of us, as Professor Huxley has said, "whirlpools on the surface of Nature;" when the whirl of exchange of particles ceases we die. We have seen that the fusion of two amoebae results in a new rejuvenated individual. Why is a mixture of two protoplasms better than one? We can frame hypotheses; we know nothing about it. What of the mind of the amoeba? A host of questions throng upon us and we can answer no one of them. All the great questions concerning life confront us here in the lowest term of the animal series, and appear as insoluble as in the highest.
Our second ancestral form is also a fresh-water animal, the hydra. This is a little, vase-shaped animal, which usually lives attached to grass-stems or sticks, but has the power to free itself and hang on the surface of the water or to slowly creep on the bottom. The mouth is at the top of the vase, and the simple, undivided cavity within the vase is the digestive cavity. Around the mouth is a ring of from four to ten hollow tentacles, whose cavities communicate freely underneath with the digestive cavity. Not only is food taken in at the mouth, but indigestible material is thrown out here. The animal may thus be compared to a nearly cylindrical sack with a circle of tubes attached to it above. The body consists of two layers of cells, the ectoderm on the outside and the entoderm lining the digestive cavity. Between these two is a structureless, elastic membrane, which tends to keep the body moderately expanded.
The food is captured by the tentacles; but digestion takes place only partially in the digestive cavity, for each surrounding cell engulfs small particles of food and digests them within itself. The entodermal cells behave in this respect much like a colony of amoebae. The cells of both layers have at their bases long muscular fibrils, those of the ectodermal cells running longitudinally, those of the entoderm transversely. The animal can thus contract its body in both directions, or, if the body contain water and the transverse muscles are contracted, the pressure of the water lengthens the body and tends to extend the tentacles.
On the outside of the elastic membrane, just beneath the ectoderm, is a plexus or cobweb of nervous cells and fibrils. As in every nervous system, three elements are here to be found. 1. An afferent or sensory nerve-fibril, which under adequate stimulus is set in vibration by some cell of the epidermis or ectoderm, which is therefore called a sensory cell. 2. A central or ganglion cell, which receives the sensory impulse, translates it into consciousness, and is the seat of whatever powers of perception, thought, or will the animal possesses. This also gives rise to the efferent or motor impulses, which are conveyed by (3) a motor fibril to the corresponding muscle, exciting its contraction. But there are also nerve-fibrils connecting the different ganglion cells, so that they may act in unison. In the higher animals we shall find these central or ganglion cells condensed in one or a few masses or ganglia. But here they are scattered over the whole surface of the elastic supporting membrane.
The reproductive organs for the production of eggs and spermatozoa form little protuberances on the outside of the body below the tentacles. But hydra reproduces mostly by budding; new individuals growing out of the side of the old one, like branches from the trunk of a tree, but afterward breaking free and leading an independent life. There are special forms of cells besides those described; nettle cells for capturing food, interstitial cells, etc., but these do not concern us.
The distance from the single-celled amoeba to hydra is vast, probably really greater than that between any other successive terms of our series. It may therefore be useful to consider one or two intermediate forms and the parallel embryonic stages of higher animals, and to see how the higher many-celled animal originates from the unicellular stage.
The amoeba is an illustration of a great kingdom of similar, practically unicellular forms, which have played no unimportant part in the geological history of the globe. These are the protozoa. They include, first of all, the foraminifera, which usually have shells composed of carbonate of lime. These shells, settling to the bottom of the ocean, have accumulated in vast beds, and when compacted and raised above the surface, form chalk, limestone, or marble, according to the degree and mode of their hardening.
The protozoa include also the flagellata, a great, very poorly defined mass of forms occupying the boundary between the plant and animal kingdoms. They are usually unicellular, and their protoplasm is surrounded by a thin, structureless membrane. This prevents their putting out pseudopodia as organs of motion. Instead of these they have at one end of the ovoid or pear-shaped body a long, whiplash-like process or thread, a flagellum, and by swinging this they propel themselves through the water. These flagellata seem to have a rather marked tendency to form colonies. The first individual gives rise to others by division. But the division is not complete; the new individuals remain connected by the undivided rear end of the body. And such a colony may come to contain a large number of individuals.
Such a colony is represented by magosphaera. This is a microscopic globular form, discovered by Professor Haeckel on the coast of Norway. It consists of a large number of conical or pear-shaped individual cells, whose apices are turned toward the centre of the sphere. The cells are cemented together by a mucilaginous substance. Around their exposed larger ends, which form the surface of the sphere, are rows of flagella, by whose united action the colony rolls through the water. After a time each individual absorbs its flagella, the colony is broken up, the different individuals settle to the bottom, and each gives rise by division to a new colony. This group of cells may be considered as a colony or as an individual. Each term is defensible.
Volvox is also a spheroidal organism, composed often of a very large number of flagellated cells. But it differs from magosphaera in certain important respects. In the first place its cells have chlorophyl, the green coloring matter of plants. It lives therefore on unorganized fluid nourishment, carbon dioxide, nitrates, etc. It is a plant. But certain characteristics render it probable that it once lived on solid food and was therefore an animal. For where almost the sole difference between plants and animals is in the fluid or solid character of their food, a change from the one form into the other is not as difficult or improbable as one might naturally think. And plants and animals are here so near together, and travelling by roads so nearly parallel, that, even if volvox never was an animal, it might still serve very well to illustrate a stage through which animals must have passed.
The cells of volvox do not form a solid mass, but have arranged themselves in a single layer on the outer surface of the sphere. For a time, under favorable circumstances, volvox reproduces very much like magosphaera, and each cell can give rise to a new, many-celled individual. But after a time, especially under unfavorable circumstances, a new mode of reproduction appears. Certain cells withdraw from the outer layer into the interior of the colony. Here they are nourished by the other cells and develop into true reproductive elements, eggs and spermatozoa. Fertilization, that is, the union of egg and spermatozoon, or mainly of their nuclei, takes place; and the fertilized egg develops into a new organism. But the other cells, which have been all the time nourishing these, seem now to lack nutriment, strength, or vitality to give rise to a new colony. They die.
We find thus in volvox division of labor and corresponding difference of structure or differentiation; certain cells retain the power of fusing with other corresponding cells, and thus of rejuvenescence and of giving rise to a new organism. And these cells, forming a series through all generations, are evidently immortal like the protozoa. Natural death cannot touch them. These are the reproductive cells. The other cells nourish and transport them and carry on the work of excretion and respiration. These latter correspond practically to our whole body. We call them somatic cells. In volvox they are entirely subservient to, and exist for, the reproductive cells, and die when they have completed their service of these. The body is here only a vehicle for ova. Furthermore, in volvox there has arisen such an interdependence of cells that we can no longer speak of it as a colony. The colony has become an individual by division of labor and the resulting differentiation in structure. |
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