Evolution of to-day; a summary of the theory of evolution as held by scientists at the present time, and an account of the progress made by the discussions and investigations of a quarter of a century

Front matter

Boston

Medical Library

8 The Fenway

Preface

Much misunderstanding exists, even in the minds of educated people, concerning the relation of the thinking world to the theory of evolution. Comparatively few, except those who have made special study of the subject, are aware even of the sort of arguments which have led scientists to accept evo^ lution. The question is, however, too important for any educated person to be satisfied with ignorance. The excuse for the present book is to fill a vacancy in our literature : to give for those who are interested in the vital questions of the age a brief account of this theory as it stands to-day in the minds of scientists. Much advance has been made since the time of Darwin's first writings. Some of his claims have been substantiated and some disproved. His own theory has been examined, tested, and partially abandoned, and others have been advanced in its place. This book is intended to indicate as nearly as possible the foundation which the theory has built for itself. I shall therefore attempt to summarize the various lines of arguments advanced and discussed upon all sides ; to enumerate the important difficulties which have arisen, together with the

IV EVOLUTION OF TO-DAY.

evolutionists' answers ; and briefly to consider the most important of the theories of evolution which science has produced ; to give, in short, a summary of the evolutionary thoughts of the past quarter of a century.

These pages are intended for those who, having an interest in the question, have neither the time nor the requisite knowledge of biology to read the numerous special discussions upon the various phases of the subject. The works of Darwin and Spencer are too ponderous for any except special students. Frequently, indeed, their abundance of detail somewhat obscures the general line of argument. For this reason, readers who are not scientists frequently fail to perceive the force of the arguments, even after they have carefully read the books of these authors. I shall therefore try to free the arguments as much as possible from detail, only mentioning special cases for the purpose of illustration. It will be understood that the generalized statements made are supported by numerous facts, even though in many cases only the bare statement is given.

The subject will be treated as a scientific question, with only a word here and there regarding its relation to other lines of thought. Evolution, if true, is simply a law, and as such should be treated as any other scientific law. It is true that the relation of this question to theology, philosophy, and metaphysics is of the highest importance ; but no more so than that of other laws. Science must first decide upon the existence of the law and its work-

PRE FA CE. V

ing in nature. If it be found to express a fact, other lines of thought must determine its significance. No law is self-sufificient, and evolution no more explains itself than does the law of gravitation.

The arguments advanced in these pages are, with few exceptions, such as may be found elsewhere in the various discussions upon the subject. I do not, however, consider it desirable to give authorities, since the arguments have by this time become the common property of the world. These arguments I shall try to state as fairly as possible ; and when a direct statement is made, it may be understood as one which is almost, if not universally, acknowledged. It is of course impossible wholly to eliminate the factor of personal opinion ; but in most cases the conclusions drawn are those which have been arrived at by students in general, and are not the opinions of individuals.

Table Of Contents

PAGE

Introduction — What is Evolution ? . . i

Original meaning of the term in scientific literature — Evolution and Darwinism — Evolution and theology — Prevalence of the evolutionary theory to-day.

I. Are Species Mutable ? 22

Immutability of species — Variation — Causes of variation — Limits of variation — Are species stable ? — Sterility of hybrids and fertility of mongrels — Indirect evidence from the relations of animals ; From fossils, from reversions — Summary.

II

Classification of the Organic World . . 53 Existence and significance of a classification — The explanation of Cuvier — The explanation of evolution — The relation of species expressed by a branching structure — Reasons for this conclusion — Value of the tree-like classification — Application of the theory to the explanation of homology — Homology in general — Serial homology — Rudimentary organs — Aborted organs — Nascent organs — Summary.

III. Life During the Geological Ages ... 89

Significance of the evidence — Imperfection of the record —

First appearance of life in the Silurian age — Difficulty in

regard to time — Absence of numerous generalized forms in

vii

VIU EVOLUTION OF TO-DAY.

PAGE

the Silurian — Diversity of Silurian life — Recent discoveries of connecting links — Geological position of these links — Development of the brain of mammals — Paleobotony — Summary

IV. Embryology 120

Importance of embryology — Embryology a repetition of past history — (i) Truth of this assumption, as shown by comparison of embryology vs'ith paleontology ; with a hypothetical history drawn from classification — Contradictions arising and their explanation — Result of previous considerations — Embryology as an assistance in classifying animals. (2) Significance of the parallel. (3) Application of the principle — Difficulties to be overcome in drawing a history from embryology— Abundance of hypothetical stages necessary — Embryological history of animals in general — Early divergence of types from a common point — Summary.

V. Geographical Distribution . . . . 165

Complexity of the factors — Animals not distributed according to climate — Laws of distribution which should follow if the descent theory is true — Relation of the present to the past — Zoological regions — Present distribution of species, genera, families, and orders — Do barriers limit the areas of distribution ? — Oceanic islands — Bermudas — Galapagos islands — St. Helena — Summary.

VI. Darwin's Explanation of Evolution . . 203

Summary of the evidence — Darwinism — Incompleteness of Darwinism — Difficulties from the slowness of the modification ; from the minuteness of changes — Transitional stages wanting — Specific chai-acters not always useful — Ornamental structures — Tendency toward elimination by crossing — Development of organs by small steps — Similarity in independently acquired organs — Mimicry — Sterile insects — Summary.

Contents

IX

VII. Page

More Recent Attempts to Explain Evolution 244

Necessity of additions to the theory of natural selection — Theory of migration of Wagner — Internal factors in evolution— Tendencies toward progression, Nageli — Extraordinary births, Mivart — Neo-Lamarckianism, the American school — Heredity — Brooks' theory of heredity and the cause of simultaneous variation — Summary.

YIII.

The Evolution of Man 288

Reason for a separate consideration of this subject — Man's physical nature — Geological evidence is lacking — Man as an intelligent animal — Method by which the evolutionist accounts for man's great intellect — Evidence from fossils impossible— Instinct and intelligence — Emotions — Knowledge of tools — Language — Consciousness — Power of improvement— Power of abstract ideas — Various intuitions — Moral nature — Religion, reverence, belief in immortality — Conscience— Darwin's explanation of conscience — Chief point where this explanation fails — Summary — Man according to all theories is radically distinct from other animals — General summary and conclusion.

Index

EVOLUTION OF TO-DAY.

Introduction

It is now a full quarter of a century since the publication of Darwin's " Origin of Species " opened to the world a new line of thought. Not only in science did this book offer an untrodden field for investigation, but its influence has extended to all other departments of learning. The general idea of evolution which this book brought into prominent notice has invaded the domain of philosophy, mental science, philology, and even our conceptions of religion and revelation have been modified by it. Hardly a line of study can be taken up without meeting at the outset this question of origin. Whatever may be the conclusion as to the truth of the ideas embodied in this work of Darwin, no one will fail to recognize that they have had an enormous influence upon the thought of the age. We read everywhere of evolution, evolution of the universe, of life, of intellect, of morals, of language ; and even artificial products are viewed under a like law, and the evolution of the steamboat or of the steam-engine is not an unfamiliar phrase. All this

2 E VOL UTION OF TO-DA V.

is, largely at least, the outcome of the theories first advanced and discussed by Darwin.

It is impossible that twenty-five years of mental activity could have passed without adding much to the evidence both in favor of and against the views of Darwin. Evolution, using the term in a general sense, has been applied to every possible notion ; its meaning has been expanded and contracted ; every realm of science has been searched both for proof and disproof of the idea ; facts have been collected from all sources both relevant and irrelevant, until the amount of matter which has been written bearing upon some of the numerous phases of the question is so great as to make it hopeless for any one to attempt to fathom it all. The amount of evidence which various investigators have brought forward is so great, and the facts are so varied, that no one with the slightest bias of opinion has any diflficulty in finding arguments for almost any view. This is well shown by the numerous secondary theories which have been advanced in connection with the general one, some of which are contradictory, but all well supported by facts. Even on the general theory of evolution itself, so varied are the data collected, that neither friends nor foes have the slightest difificulty in selecting from the large stores of facts many which support their views. Quite frequently indeed, the same set of facts is made to serve on both sides, as an argument for and against evolution. If one desires to do so it is easy to make out a case on either side. By confining the attention to favorable arguments alone, evolution can be made to appear demonstrated ; and by considering the difficulties, alone, an opposite result may be obtained. Unfortunately most of our publications take one of these two courses, and are, therefore, in a measure unsatisfactory. It requires more extensive reading and more careful balancing of evidence than most readers are inclined to give, to perceive the real force of the arguments.

What is Evolution ?

It is necessary at the outset to inquire into the meaning of the term evolution. So varied has been the discussion, and so numerous the senses in which the word is used, that to say that one accepts evolution conveys no adequate idea, for it may mean much or it may mean almost nothing. When first used, the word had a very different significance from that which now is attached to it. It was believed by certain naturalists of the last century that there then existed in the &^^ an individual precisely like the adult, except that it was too small to be visible. The development of the e^^ was simply the groivth of this minute individual, a growth precisely similar to that taking place in animals after birth. This theory was called evolution. Very soon, however, it was disproved, for a few observations served to show that no such simple growth took place. But the word evolution was still retained to apply to development in general, and thus for a long time it simply referred to the development of the individual from the ^^^. But slowly the word came to be applied to a different series of phenomena, while it is still occasionally used in its earlier significance. It has come almost universally to refer not to the development of the individual from the &^%, but to the development of the whole existing order of nature from the past. In this sense, too, it has a wide range. On the one hand, it may mean a simple advance of one generation over another in any particular. Man's rise in intelligence during the last two thousand years is said to be evolution ; or the gradual growth in the efficacy of weapons of war may be called an evolution.

But on the other hand, the term has been stretched in its meaning until it covers the origin of all things, and with certain philosophers it is supposed to be a universal law which explains the present universe. Foremost among these stand Spencer and Haeckel, who believe that, starting with the existence of a homogeneous nebular mass, the result by the simplest natural laws would be a system such as we nov/ find. Spencer tells us that by the unequal action of force upon this nebula, its homogeneity is soon broken up, and the nebula thus becomes resolved into a number of unequal masses. By the continued action of the same persistent force, the masses concentrate, and the planets appear with their satellites. Later, by the same process, atoms of carbon unite with atoms of hydrogen, nitrogen, and oxygen, and the result is protoplasm ; and thus life arises spontaneously. Life now goes on developing, the old giving rise to new and constantly higher and more complex forms, until the result is the present vegetable and animal world, which has thus arisen by ordinary generation. Finally, by the continued development of the nervous system, the intellect makes its appearance, rises higher and higher, until it reaches the grade which we find in man. Evolution is here, then, a comprehensive theory, covering the slow growth of the whole universe by the simple action and interaction of force, according to natural law. But even in this most comprehensive sense the theory does not attempt to explain the origin of the universe. To start with, it assumes the existence of force and of a homogeneous mass of matter.

Between the two extremes may be found almost every grade, for evolution, when defined, means simply that the past has given rise to the present by the simple process of development according to natural law. But, although the word may thus mean almost any thing, and does have different significance with different thinkers, it has, nevertheless, in scientific literature, a tolerably definite meaning. Among scientists the term seldom covers the amount of ground which is included in Spencer's theory, nor does it ever stop at the other meaningless extreme. As ordinarily used in most scientific books to-day, evolution, organic evolution, and the theory of descent are practically synonymous terms, and each of these is used to indicate the theory that all species of animals and plants existing to-day have been derived from others living in the past, by direct descent, and that they will themselves give rise in the future to other still different species. It further implies that if the histories of all animals living to-day could be traced backward, they would all be found to converge, until finally they met at a common point of union, which would represent a common ancestor living in the remote past. In short, evolution, as the term is commonly understood to-day, is chiefly a denial of the former belief that species were independently created, and the replacement of this belief with its opposite. It assumes that no species is an independent creation, but that all are derived from past forms now mostly extinct. This is evolution as Darwin understood it ; this is the common understanding of the term to-day in scientific literature ; and this is the question which has been so thoronghly investigated in the last twenty-five years.

As thus defined, it is easy to see that the theory is not complete, since nothing is said as to the origin of life. The essential idea which underlies the whole theory is that species have had a natural rather than a supernatural origin ; and it is evident that unless we give a natural explanation of the origin of life, the idea is lacking at its very foundation. Nor is this all ; for the same logical necessity will compel us to explain, in a similar way, the origin of the world and the solar system, and thus to reach a theory something like that of Spencer. But even this theory does not reach any bottom, for it assumes the existence of the nebula, and Spencer found it necessary to put behind and beneath his system an " unknowable," which he considered the same as the God of theology. It is therefore impossible to make evolution a complete theory.

Since, then, this is a logical impossibility, it is best to admit the fact and confine our conception of evolution to the realm where there is evidence for it. Now, at the beginning of life there is a break in the series. There is not yet the slightest evidence that living matter could arise from non-living matter. All of the most recent experiments have certified this conclusion. Scientists, perceiving it a logical necessity of these views to believe that life could have arisen from inorganic matter, have had naturally a great desire to prove this possibility. The fact that spontaneous generation is universally given up is therefore a testimony to the cogency of the conclusion and the honesty of the investigators. But on the other hand, it is evident enough that while the experiments of Tyndall and others prove that life cannot arises pontaneously in the conditions under which they have performed their experiments — i. e., in closed flasks containing boiled solutions, they by no means prove that spontaneous generation could not have taken place under other different circumstances. We can know nothing as to what may have taken place under different conditions. It is equally possible for one side to claim that the experiments teach that life cannot arise spontaneously, and for the other side to claim that while it does not do so now, it might have been possible under very different circumstances in times past. In short, the question is not open to investigation. It is impossible to prove that spontaneous generation could never have occurred ; and it is extremely improbable that the opposite view will ever be demonstrated. All that can be done is to discuss the question from theoretical grounds. There is then a break at the beginning of life, since spontaneous generation can be neither proved nor disproved. This fact makes it far preferable for the present at least to confine the term evolution, in our ordinary discussion, as Darwin did, to the development of life, without including any theory as to its origin ; realizing all the while that as thus stated the theory is not complete. If we do coniine the term to these limits we have a theory which is open to investigation, and which may some time be approximately demonstrated. But if we attempt to include all that Spencer understands by the term, there is little hope that we can advance beyond hypothesis. Scientists, therefore, as a rule, restrict the term to the development of living organisms. It is the object of the following pages to discuss the question in this sense, as a scientific theory, therefore, without reference to the deeper metaphysical problems underlying the more comprehensive significance of evolution as applied to the origin of the universe. Whenever the term evolution is used in the following pages, it is in the sense above indicated, and is synonymous with the terms organic evolution and the theory of descent.

Are there any other breaks in the chain of continuity which may make it wise to limit still further the meaning of evolution ? It is claimed by many that such a break is found in man ; not so far as his body is concerned, but because he represents a new order, in intellect and morality. This question is reserved for a separate chapter. But more than this, it has been held by certain naturalists that species have arisen from several distinct points, and not from one. They would say that there have been a number of points of origin, one for each of the sub-kingdoms. But this position is hardly a tenable one and is now generally abandoned. It is, of course, perfectly possible that such might have been the history of animals, even upon the theory of evolution, but there is not the slightest evidence that such was the case. On the contrary, as we shall see later, the evidence is such as to apply to all species alike, and if its force is admitted at all, it must be admitted as linking the organic world into a single unit, and not into several. The sub-kingdoms are united together at the bottom, and if evolution is admitted at all, it must apply to the whole organic world. While, then, it is desirable to confine the subject to limits where it can be investigated and attested by facts, it is equally desirable to avoid the other extreme and fail to see that evolution must cover all organic species or none.

Evoliitio7i is not Darwinism.

We have now reached a conclusion as to what is ordinarily meant by evolution, and such was Darwin's understanding of the term. But it must not be confounded with Darwinism. Evolution is simply a theory as to the method by which species have been introduced into the world, entirely independent of any idea as to the causes which have brought about their introduction. Darwinism is evolution ; but it lO EVOLUTION OF TO-DAY.

is more than this ; it is at the same time an attempt at an explanation of the causes of evolution. It not only claims that species have been slowly evolved from each other, but it also gives an account of the manner in which they have arisen, and the laws which govern their gradual modification. It is, therefore, possible to accept evolution and to reject Darwinism completely ; to believe that species have been evolved from each other, but to deny that Darwin has discovered the causes of this evolution. And so with various other theories of evolution, of which science has proposed several. All agree as to the evolution of species from each other, but no two explain the fact in the same manner. For we must recognize two quite different questions in considering the subject. The first is as to the fact of evolution. We must discover, if possible what has been the history of organisms ; whether each species is to be considered as an abrupt innovation, utterly independent of all others — i. e., a special creation, or whether species have been derived from each other by the ordinary methods of reproduction aud slow change. If it is discovered that the evidence is sufficient to prove evolution to be a fact, or to render it probable, a second and more difficult question remains. We must discover what are the laws which regulate this evolution, and must determine how species have been derived from each other, whether slowly or abruptly, whether by internal or external forces, and other problems of like nature. In reality these two questions have been considered simultaneously, all theories of evolution attempting

INTRODUCTION. II

to answer both questions ; or more frequently they assume evolution and attempt simply to find an explanation of the fact.

In the following pages these two questions will be considered separately as far as possible, though they are so intimately connected as to make a complete separation impossible. In the first five chapters we shall discuss the question whether evolution be a fact. Here we shall consider the various arguments which have been adduced to prove that species have been derived from each other, and the various difificulties and objections which have arisen against the unhesitating acceptance of this view. In the sixth and seventh chapters we will examine the several theories of evolution held by different scientists, which attempt to explain the fundamental fact, and to give the causes which have produced the development of new species.

Darwinism proper is, then, not evolution, but its explanation. Darwin's contribution to science was his law of natural selection, a principle which he believed to be the chief cause of the development of new species. Darwin did not originate the theory of evolution, although it is rightly associated with his name. If the writings of Descartes, Leibnitz, and Goethe be carefully studied, the beginnings of the modern ideas involved in the term can be traced. Very indefinite they were, it is true, and so they remained until about the beginning of the present century. At this time a French naturalist, Lamarck, formulated a logical and consistent theory of evolution, a theory which agreed in almost all respects with the one that is still held at the present day by many American naturalists. He not only believed in the origin of species from each other, but he gave an explanation of his theory. And the explanation which he gave is accepted to-day by many naturalists as being nearer to the truth than that of Darwin. But Lamarck was ahead of his age, and the world was not ready for his views. He had, moreover, the great authority of Cuvier against him, and the weight of Cuvier's name soon caused Lamarck and his evolution to sink into oblivion, to reappear occasionally at fitful periods as the next half century passed. In 1859 ^^^ publication of Darwin's " Origin of Species " brought the old view once more into prominence under a new light. For twenty years Darwin had been patiently investigating the theory before he published a word, and when he did appeal to the world he not only could give very strong arguments for accepting the general theory of evolution, but he offered at the same time an extremely simple and comprehensive explanation. A consideration of this explanation we must defer ; but so strong were Darwin's arguments, and so skilfully were they handled, that the scientific world began immediately to discuss the question. Not a little of Darwin's influence was due to the great candor of his discussion and the readiness with which he acknowledged the difficulties which he could not meet. From that time evolution has been constantly before the world. Not only has much evidence been collected in the endeavor to prove or disprove evolution, but the explanation offered by

Darwin has been subjected to thorough examination. It has been carefully applied to all sorts of facts ; its weak points and strong points have been discovered ; and new theories have been suggested in its place. The prominence of this question in modern times is therefore due to the influence of Darwin, and his name will always be associated with it, even though he was not the originator of the theory of evolution, and though his own explanation of the theory should be largely abandoned.

Evolution mid TJieology.

From the very first, evolution has been obliged to contend with prejudices arising partly from ignorance of the theory and partly from the natural tendency to cherish old ideas. The current conflict of science and religion has at times been vigorous over this question. Scientists, by this theory, offered to remove a whole series of miraculous events from nature. Species, which were before looked upon as the direct handiwork of God, were now regarded as the results of natural law. Evolution was supposed to be in contradiction to revelation, which had always been supposed to teach the special creation of species. Atheistic scientists claimed to have aimed a heavy blow at theism by this theory, and the theists quite naturally attempted to destroy the weapon before the blow reached them. The weapon has not been destroyed, but it has been found to be harmless, for theism stands unmoved by evolutionary theories.

The arguments which have been most potent in causing a rejection of evolution have frequently been of no scientific importance. Instead of trying to find out whether evolution is true, many begin at the other end. They select certain unpleasant results which they say will follow if the theory be true, and then proceeding to show that these results cannot be accepted, assume to have disproved the theory. One voluminous book, published within a year, assumes to start with, that if evolution were true Christianity would be overthrown, and with this as a foundation proceeds to demolish the theory. But such reasoning is worse than worthless ; it is a positive injury both to science and religion, because it gives a false idea of both. Christianity does not want such defence, nor does science care in the least for such attacks. The truth of the theory of evolution must be decided by the evidence which can be adduced, and not by the results which we may think would follow.

Hugh Miller used to say that it was the misfortune of theology to be fifty years behind science. As soon as science advances any theory, theology thinks to discover it to be contrary to revelation, and immediately attempts to prove this contradiction. After much time is spent in such discussion the discovery is made that science has in the meantime demonstrated the theory in question. Theology is then obliged to retrace its steps ; and usually discovers very soon that its earlier interpretations were erroneous. This has been the history of almost all scientific theories, and thus according to Hugh Miller theology is fifty years behind science.

Fortunate enough perhaps it is, for this fact prevents a too precipitous advance, and compels science to give good reasons for every step it takes.

In regard to evolution, however, it has not required fifty years to show that a belief in religion is not materially affected by its acceptance. Already our leading thinkers among theologians, as well as elsewhere, have recognized that the question is a scientific one purely, and must be decided upon scientific grounds ; whether it is decided in the affirmative or the negative it does not trouble the belief in theism. Some people appear to think that to explain any phenomena by law, is to take it out of the hands of the Creator ; and hence, if all things could be reduced to law, there would be no longer any need for a Creator. But this is plainly far from the truth. Even if evolution be admitted to its fullest extent, it does not explain creation ; it only proves continuity. Darwinism itself explains the origin of nothing. It simply claims that the universal survival of the fittest varieties would slowly give rise to new species. And even the other theories which attempt to account for these varieties do not touch any bottom, although they go deeper into the matter. It is an old saying, that evolution cannot exceed involution ; a saying which is sometimes held up to ridicule. But in its true sense it expresses an undoubted truth. Evolution, using the term now as Spencer uses it, does not create, it only modifies. Were it not true that under all nature there existed harmonious laws ; were it not true that matter possessed certain properties;