CHAPTER XIX

THE RISE OF EVOLUTIONARY THOUGHT

A current of evolutionary thought can be traced through the literature dealing with organic nature from ancient times. It began as a small rill among the Greek philosophers and dwindles to a mere thread in the Middle Ages, sometimes almost disappearing, but is never completely broken off. Near the close of the eighteenth century it suddenly expands, and becomes a broad and prevailing influence in the nineteenth century. Osborn, in his book, _From the Greeks to Darwin_, traces the continuity of evolutionary thought from the time of the Greek philosophers to Darwin. The ancient phase, although interesting, was vague and general, and may be dismissed without much consideration. After the Renaissance naturalists were occupied with other aspects of nature-study. They were at first attempting to get a knowledge of animals and plants as a whole, and later of their structure, their developments, and their physiology, before questions of their origin were brought under consideration.

Opinion before Lamarck.--The period just prior to Lamarck is of particular interest. Since Lamarck was the first to give a comprehensive and consistent theory of evolution, it will be interesting to determine what was the state of opinion just prior to the appearance of his writings. Studies of nature were in such shape at that time that the question of the origin of species arose, and thereafter it would not recede. This was owing mainly to the fact that Ray and Linnæus by defining a species had fixed the attention of naturalists upon the distinguishing features of the particular kinds of animals and plants. Are species realities in nature? The consideration of this apparently simple question soon led to divergent views, and then to warm controversies that extended over several decades of time.

The view first adopted without much thought and as a matter of course was that species are fixed and constant; _i.e._, that the existing forms of animals and plants are the descendants of entirely similar parents that were originally created in pairs. This idea of the fixity of species was elevated to the position of a dogma in science as well as in theology. The opposing view, that species are changeable, arose in the minds of a few independent observers and thinkers, and, as has already been pointed out, the discussion of this question resulted ultimately in a complete change of view regarding nature and man's relation to it. When the conception of evolution came upon the scene, it was violently combated. It came into conflict with the theory designated special creation.

Views of Certain Fathers of the Church.--And now it is essential that we should be clear as to the sources of this dogma of special creation. It is perhaps natural to assume that there was a conflict existing between natural science and the views of the theologians from the earliest times; that is, between the scientific method and the method of the theologians, the latter being based on authority, and the former upon observation and experiment. Although there is a conflict between these two methods, there nevertheless was a long period in which many of the leading theological thinkers were in harmony with the men of science with reference to their general conclusions regarding creation. Some of the early Fathers of the Church exhibited a broader and more scientific spirit than their successors.

St. Augustine (353-430), in the fifth century, was the first of the great theologians to discuss specifically the question of creation. His position is an enlightened one. He says: "It very often happens that there is some question as to the earth or the sky, or the other elements of this world ... respecting which one who is not a Christian has knowledge derived from most certain reasoning or observation" (that is, a scientific man); "and it is very disgraceful and mischievous and of all things to be carefully avoided, that a Christian speaking of such matters as being according to the Christian Scriptures, should be heard by an unbeliever talking such nonsense that the unbeliever, perceiving him to be as wide from the mark as east from west, can hardly restrain himself from laughing." (Quoted from Osborn.)

Augustine's view of the method of creation was that of derivative creation or creation _causaliter_. His was a naturalistic interpretation of the Mosaic record, and a theory of gradual creation. He held that in the beginning the earth and the waters of the earth were endowed with power to produce plants and animals, and that it was not necessary to assume that all creation was formed at once. He cautions his readers against looking to the Scriptures for scientific truths. He said in reference to the creation that the days spoken of in the first chapter of Genesis could not be solar days of twenty-four hours each, but that they must stand for longer periods of time.

This view of St. Augustine is interesting as being less narrow and dogmatic than the position assumed by many theologians of the nineteenth century.

The next theologian to take up the question of creation was St. Thomas Aquinas (1225-1274) in the thirteenth century. He quotes St. Augustine's view with approval, but does not contribute anything of his own. One should not hastily conclude, however, because these views were held by leaders of theological thought, that they were universally accepted. "The truth is that all classes of theologians departed from the original philosophical and scientific standards of some of the Fathers of the Church, and that special creation became the universal teaching from the middle of the sixteenth to the middle of the nineteenth centuries."

The Doctrine of Special Creation.--About the seventeenth century a change came about which was largely owing to the writings and influence of a Spanish theologian named Suarez (1548-1617). Although Suarez is not the sole founder of this conception, it is certain, as Huxley has shown, that he engaged himself with the questions raised by the Biblical account of creation; and, furthermore, that he opposed the views that had been expressed by Augustine. In his tract upon the work of the six days (_Tractatus de opere sex dierum_) he takes exception to the views expressed by St. Augustine; he insisted that in the Scriptural account of creation a day of twenty-four hours was meant, and in all other cases he insists upon a literal interpretation of the Scriptures. Thus he introduced into theological thought the doctrine which goes under the name of special creation. The interesting feature in all this is that from the time of St. Augustine, in the fifth century, to the time when the ideas of Suarez began to prevail, in the seventeenth, there had been a harmonious relation between some of the leading theologians and scientific men in their outlook upon creation.

The opinion of Augustine and other theologians was largely owing to the influence of Aristotle. "We know," says Osborn, "that Greek philosophy tinctured early Christian theology; what is not so generally realized is that the Aristotelian notion of the development of life led to the true interpretation of the Mosaic account of the creation.

"There was in fact a long Greek period in the history of the evolutionary idea extending among the Fathers of the Church and later among some of the schoolmen, in their commentaries upon creation, which accord very closely with the modern theistic conception of evolution. If the orthodoxy of Augustine had remained the teaching of the Church, the final establishment of evolution would have come far earlier than it did, certainly during the eighteenth century instead of the nineteenth century, and the bitter controversy over this truth of nature would never have arisen."

The conception of special creation brought into especial prominence upon the Continent by Suarez was taken up by John Milton in his great epic _Paradise Lost_, in which he gave a picture of creation that molded into specific form the opinion of the English-speaking clergy and of the masses who read his book. When the doctrine of organic evolution was announced, it came into conflict with this particular idea; and, as Huxley has very pointedly remarked, the new theory of organic evolution found itself in conflict with the Miltonic, rather than the Mosaic cosmology. All this represents an interesting phase in intellectual development.

Forerunners of Lamarck.--We now take up the immediate predecessors of Lamarck. Those to be mentioned are Buffon, Erasmus Darwin, and Goethe.

Buffon (1707-1788) (Fig. 116), although of a more philosophical mind than many of his contemporaries, was not a true investigator. That is, he left no technical papers or contributions to science. From 1739 to the time of his death he was the superintendent of the _Jardin du Roi_. He was a man of elegance, with an assured position in society. He was a delightful writer, a circumstance that enabled him to make natural history popular. It is said that the advance sheets of Buffon's _Histoire Naturelle_ were to be found on the tables of the boudoirs of ladies of fashion. In that work he suggested the idea that the different forms of life were gradually produced, but his timidity and his prudence led him to be obscure in what he said.

Packard, who has studied his writings with care, says that he was an evolutionist through all periods of his life, not, as is commonly maintained, believing first in the fixity of species, later in their changeability, and lastly returning to his earlier position. "The impression left on the mind after reading Buffon is that even if he threw out these suggestions and then retracted them, from fear of annoyance or even persecution from the bigots of his time, he did not himself always take them seriously, but rather jotted them down as passing thoughts. Certainly he did not present them in the formal, forcible, and scientific way that Erasmus Darwin did. The result is that the tentative views of Buffon, which have to be with much research extracted from the forty-four volumes of his works, would now be regarded as in a degree superficial and valueless. But they appeared thirty-four years before Lamarck's theory, and though not epoch-making, they are such as will render the name of Buffon memorable for all time." (Packard.)

Erasmus Darwin (Fig. 117) was the greatest of Lamarck's predecessors. In 1794 he published the _Zoönomia_. In this work he stated ten principles; among them he vaguely suggested the transmission of acquired characteristics, the law of sexual selection--or the law of battle, as he called it--protective coloration, etc. His work received some notice from scholars. Paley's _Natural Theology_, for illustration, was written against it, although Paley is careful not to mention Darwin or his work. The success of Paley's book is probably one of the chief causes for the neglect into which the views of Buffon and Erasmus Darwin fell.

Inasmuch as Darwin's conclusions were published before Lamarck's book, it would be interesting to determine whether or not Lamarck was influenced by him. The careful consideration of this matter leads to the conclusion that Lamarck drew his inspiration directly from nature, and that points of similarity between his views and those of Erasmus Darwin are to be looked upon as an example of parallelism in thought. It is altogether likely that Lamarck was wholly unacquainted with Darwin's work, which had been published in England.

Goethe's connection with the rise of evolutionary thought is in a measure incidental. In 1790 he published his _Metamorphosis of Plants_, showing that flowers are modified leaves. This doctrine of metamorphosis of parts he presently applied to the animal kingdom, and brought forward his famous, but erroneous, vertebrate theory of the skull. As he meditated on the extent of modifications there arose in his mind the conviction that all plants and animals have been evolved from the modification of a few parental types. Accordingly he should be accorded a place in the history of evolutionary thought.

Opposition to Lamarck's Views.--Lamarck's doctrine, which was published in definite form in 1809, has been already outlined. We may well inquire, Why did not his views take hold? In the first place, they were not accepted by Cuvier. Cuvier's opposition was strong and vigorous, and succeeded in causing the theory of Lamarck to be completely neglected by the French people. Again, we must recognize that the time was not ripe for the acceptance of such truths; and, finally, that there was no great principle enunciated by Lamarck which could be readily understood as there was in Darwin's book on the doctrine of natural selection.

The temporary disappearance of the doctrine of organic evolution which occurred after Lamarck expounded his theory was also owing to the reaction against the speculations of the school of _Natur-Philosophie_. The extravagant speculation of Oken and the other representatives of this school completely disgusted men who were engaged in research by observation and experiment. The reaction against that school was so strong that it was difficult to get a hearing for any theoretical speculation; but Cuvier's influence must be looked upon as the chief one in causing disregard for Lamarck's writings.

The work of Cuvier has been already considered in connection both with comparative anatomy and zoölogy, but a few points must still be held under consideration. Cuvier brought forward the idea of catastrophism in order to explain the disappearance of the groups of fossil animals. He believed in the doctrine of spontaneous generation. He held to the doctrine of pre-delineation, so that it must be admitted that whenever he forsook observation for speculation he was singularly unhappy, and it is undeniable that his position of hostility in reference to the speculation of Lamarck retarded the progress of science for nearly half a century.

Cuvier and Saint-Hilaire.--In 1830 there occurred a memorable controversy between Cuvier and Saint-Hilaire. The latter (Fig. 118) was in early life closely associated with Lamarck, and shared his views in reference to the origin of animals and plants; though in certain points Saint-Hilaire was more a follower of Buffon than of Lamarck. Strangely enough, Saint-Hilaire was regarded as the stronger man of the two. He was more in the public eye, but was not a man of such deep intellectuality as Lamarck. His scientific reputation rests mainly upon his _Philosophie Anatomique_. The controversy between him and Cuvier was on the subject of unity of type; but it involved the question of the fixity or mutability of species, and therefore it involved the foundation of the question of organic evolution.

Fig. 118.--Geoffroy Saint-Hilaire, 1772-1844.

This debate stirred all intellectual Europe. Cuvier won as being the better debater and the better manager of his case. He pointed triumphantly to the four branches of the animal kingdom which he had established, maintaining that these four branches represented four distinct types of organization; and, furthermore, that fixity of species and fixity of type were necessary for the existence of a scientific natural history. We can see now that his contention was wrong, but at the time he won the debate. The young men of the period, that is, the rising biologists of France, were nearly all adherents of Cuvier, so that the effect of the debate was, as previously stated, to retard the progress of science. This noteworthy debate occurred in February, 1830. The wide and lively interest with which the debate was followed may be inferred from the excitement manifested by Goethe. Of the great poet-naturalist, who was then in his eighty-first year, the following incident is told by Soret:

"Monday, Aug. 2d, 1830.--The news of the outbreak of the revolution of July arrived in Weimar to-day, and has caused general excitement. In the course of the afternoon I went to Goethe. 'Well,' he exclaimed as I entered, 'what do you think of this great event? The volcano has burst forth, all is in flames, and there are no more negotiations behind closed doors.' 'A dreadful affair,' I answered; 'but what else could be expected under the circumstances, and with such a ministry, except that it would end in the expulsion of the present royal family?' 'We do not seem to understand each other, my dear friend,' replied Goethe. 'I am not speaking of those people at all; I am interested in something very different. I mean the dispute between Cuvier and Geoffroy de Saint-Hilaire, which has broken out in the Academy, and which is of such great importance to science.' This remark of Goethe came upon me so unexpectedly that I did not know what to say, and my thoughts for some minutes seemed to have come to a complete standstill. 'The affair is of the utmost importance,' he continued, 'and you can not form any idea of what I felt on receiving the news of the meeting on the 19th. In Geoffroy de Saint-Hilaire we have now a mighty ally for a long time to come. But I see also how great the sympathy of the French scientific world must be in this affair, for, in spite of the terrible political excitement, the meeting on the 19th was attended by a full house. The best of it is, however, that the synthetic treatment of nature, introduced into France by Geoffroy, can now no longer be stopped. This matter has now become public through the discussions in the Academy, carried on in the presence of a large audience; it can no longer be referred to secret committees, or be settled or suppressed behind closed doors.'"

Influence of Lyell's Principles of Geology.--But just as Cuvier was triumphing over Saint-Hilaire a work was being published in England which was destined to overthrow the position of Cuvier and to bring again a sufficient foundation for the basis of mutability of species. I refer to Lyell's _Principles of Geology_, the influence of which has already been spoken of in Chapter XV. Lyell laid down the principle that we are to interpret occurrences in the past in the terms of what is occurring in the present. He demonstrated that observations upon the present show that the surface of the earth is undergoing gradually slow changes through the action of various agents, and he pointed out that we must view the occurrences in the past in the light of occurrences in the present. Once this was applied to animal forms it became evident that the observations upon animals and plants in the present must be applied to the life of the fossil series.

These ideas, then, paved the way for the conception of changes in nature as being one continuous series.

H. Spencer.--In 1852 came the publication of Herbert Spencer in the _Leader_, in which he came very near anticipating the doctrine of natural selection. He advanced the developmental hypothesis, saying that even if its supporters could "merely show that the production of species by the process of modification is conceivable, they would be in a better position than their opponents. But they can do much more than this; they can show that the process of modification has affected and is affecting great changes in all organisms subject to modifying influences.... They can show that any existing species, animal or vegetable, when placed under conditions different from its previous ones, immediately begins to undergo certain changes of structure fitting it for the new conditions. They can show that in successive generations these changes continue, until ultimately the new conditions become the natural ones. They can show that in cultivated plants and domesticated animals, and in the several races of men, these changes have uniformly taken place. They can show that the degrees of difference so produced are often, as in dogs, greater than those on which distinctions of species are in other cases founded. They can show that it is a matter of dispute whether some of these modified forms _are_ varieties or modified species. And thus they can show that throughout all organic nature there is at work a modifying influence of the kind they assign as the cause of these specific differences; an influence which, though slow in its action, does in time, if the circumstances demand it, produce marked changes; an influence which, to all appearance, would produce in the millions of years, and under the great varieties of conditions which geological records imply, any amount of change."

"It is impossible," says Marshall, "to depict better than this the condition prior to Darwin. In this essay there is full recognition of the fact of transition, and of its being due to natural influences or causes, acting now and at all times. Yet it remained comparatively unnoticed, because Spencer, like his contemporaries and predecessors, while advocating evolution, was unable to state explicitly what these causes were."

Darwin and Wallace.--In 1858 we come to the crowning event in the rise of evolutionary thought, when Alfred Russel Wallace sent a communication to Mr. Darwin, begging him to look it over and give him his opinion of it. Darwin, who had been working upon his theory for more than twenty years, patiently gathering facts and testing the same by experiment, was greatly surprised to find that Mr. Wallace had independently hit upon the same principle of explaining the formation of species. In his generosity, he was at first disposed to withdraw from the field and publish the essay of Wallace without saying anything about his own work. He decided, however, to abide by the decision of two of his friends, to whom he had submitted the matter, and the result was that the paper of Wallace, accompanied by earlier communications of Darwin, were laid before the Linnæan Society of London. This was such an important event in the history of science that its consideration is extended by quoting the following letter:

"London, June 30th, 1858.

"My Dear Sir: The accompanying papers, which we have the honor of communicating to the Linnæan Society, and which all relate to the same subject; _viz_., the laws which affect the production of varieties, races, and species, contain the results of the investigations of two indefatigable naturalists, Mr. Charles Darwin and Mr. Alfred Wallace.

"These gentlemen having, independently and unknown to one another, conceived the same very ingenious theory to account for the appearance and perpetuation of varieties and of specific forms on our planet, may both fairly claim the merit of being original thinkers in this important line of inquiry; but neither of them having published his views, though Mr. Darwin has for many years past been repeatedly urged by us to do so, and both authors having now unreservedly placed their papers in our hands, we think it would best promote the interests of science that a selection from them should be laid before the Linnæan Society.

"Taken in the order of their dates, they consist of:

"1. Extracts from a MS. work on species, by Mr. Darwin, which was sketched in 1839 and copied in 1844, when the copy was read by Dr. Hooker, and its contents afterward communicated to Sir Charles Lyell. The first part is devoted to _The Variation of Organic Beings under Domestication and in their Natural State_; and the second chapter of that part, from which we propose to read to the Society the extracts referred to, is headed _On the Variation of Organic Beings in a State of Nature; on the Natural Means of Selection; on the Comparison of Domestic Races and True Species_.

"2. An abstract of a private letter addressed to Professor Asa Gray, of Boston, U.S., in October, 1857, by Mr. Darwin, in which he repeats his views, and which shows that these remained unaltered from 1839 to 1857.

"3. An essay by Mr. Wallace, entitled _On the Tendency of Varieties to Depart Indefinitely from the Original Type_. This was written at Ternate in February, 1858, for the perusal of his friend and correspondent, Mr. Darwin, and sent to him with the expressed wish that it should be forwarded to Sir Charles Lyell, if Mr. Darwin thought it sufficiently novel and interesting. So highly did Mr. Darwin appreciate the value of the views therein set forth that he proposed, in a letter to Sir Charles Lyell, to obtain Mr. Wallace's consent to allow the essay to be published as soon as possible. Of this step we highly approved, provided Mr. Darwin did not withhold from the public, as he was strongly inclined to do (in favor of Mr. Wallace), the memoir which he had himself written on the same subject, and which, as before stated, one of us had perused in 1844, and the contents of which we had both of us been privy to for many years.

"On representing this to Mr. Darwin, he gave us permission to make what use we thought proper of his memoir, etc.; and in adopting our present course, of presenting it to the Linnæan Society, we have explained to him that we are not solely considering the relative claims to priority of himself and his friend, but the interests of science generally; for we feel it to be desirable that views founded on a wide deduction from facts, and matured by years of reflecting, should constitute at once a goal from which others may start; and that, while the scientific world is waiting for the appearance of Mr. Darwin's complete work, some of the leading results of his labours, as well as those of his able correspondent, should together be laid before the public.

"We have the honour to be yours very obediently,

Charles Lyell,

Jos. D. Hooker."

Personality of Darwin.--The personality of Darwin is extremely interesting. Of his numerous portraits, the one shown in Fig. 119 is less commonly known than those showing him with a beard and a much furrowed forehead. This portrait represents him in middle life, about the time of the publication of his _Origin of Species_. It shows a rather typical British face, of marked individuality. Steadiness, sincerity, and urbanity are all depicted here. His bluish-gray eyes were overshadowed by a projecting ridge and very prominent, bushy eyebrows that make his portrait, once seen, easily recognized thereafter. In the full-length portraits representing him seated, every line in his body shows the quiet, philosophical temper for which he was notable. An intimate account of his life is contained in the _Life and Letters of Charles Darwin_ (1887) and in _More Letters of Darwin_ (1903), both of which are illustrated by portraits and other pictures. The books about Darwin and his work are numerous, but the reader is referred in particular to the two mentioned as giving the best conception of the great naturalist and of his personal characteristics.

He is described as being about six feet high, but with a stoop of the shoulders which diminished his apparent height; "of active habits, but with no natural grace or neatness of movement." "In manner he was bright, animated, and cheerful; a delightfully considerate host, a man of never-failing courtesy, leading him to reply at length to letters from anybody, and sometimes of a most foolish kind."

His Home Life.--"Darwin was a man greatly loved and respected by all who knew him. There was a peculiar charm about his manner, a constant deference to others, and a faculty for seeing the best side of everything and everybody."

He was most affectionate and considerate at home. The picture of Darwin's life with his children gives a glimpse of the tenderness and deep affection of his nature, and the reverent regard with which he was held in the family circle is very touching. One of his daughters writes: "My first remembrances of my father are of the delights of his playing with us. He was passionately attached to his own children, although he was not an indiscriminate child-lover. To all of us he was the most delightful playfellow, and the most perfect sympathizer. Indeed, it is impossible adequately to describe how delightful a relation his was to his family, whether as children or in their later life.

"It is a proof of the terms on which we were, and also of how much he was valued as a playfellow, that one of his sons, when about four years old, tried to bribe him with a sixpence to come and play in working hours. We all knew the sacredness of working time, but that any one should resist sixpence seemed an impossibility."

Method of Work.--Darwin's life, as might be inferred from the enduring quality of his researches, shows an unswerving purpose. His theory was not the result of a sudden flash of insight, nor was it struck out in the heat of inspiration, but was the product of almost unexampled industry and conscientious endeavor in the face of unfavorable circumstances. Although strikingly original and independent as a thinker, he was slow to arrive at conclusions, examining with the most minute and scrupulous care the ground for every conclusion. "One quality of mind that seemed to be of especial advantage in leading him to make discoveries was the habit of never letting exceptions pass unnoticed." He enjoyed experimenting much more than work which only entailed reasoning. Of course, he was a great reader, but for books as books he had no respect, often cutting large ones in two in order to make them easier to hold while in use.

Darwin's Early Life.--Charles Darwin was born in 1809 at Shrewsbury, England, of distinguished ancestry, his grandfather being the famous Dr. Erasmus Darwin, the founder, as we have seen, of a theory of evolution. In his youth he gave no indication of future greatness. He was sent to Edinburgh to study medicine, but left there after two sessions, at the suggestion of his father, to study for the Church. He then went to the University of Cambridge, where he remained three years, listening to "incredibly dull lectures." After taking his baccalaureate degree, came the event which proved, as Darwin says, "the turning-point of my life." This was his appointment as naturalist on the surveying expedition about to be entered upon by the ship _Beagle_. In Cambridge he had manifested an interest in scientific study, and had been encouraged by Professor Henslow, to whom he was also indebted for the recommendation to the post on the _Beagle_. An amusing circumstance connected with his appointment is that he was nearly rejected by Captain Fitz-Roy, who doubted "whether a man with such a shaped nose could possess sufficient energy and determination for the voyage."

Voyage of the Beagle.--The voyage of the _Beagle_ extended over five years (1831-1836), mainly along the west coast of South America. It was on this voyage that Darwin acquired the habit of constant industry. He had also opportunity to take long trips on shore, engaged in observation and in making extensive collections. He observed nature in the field under exceptional circumstances. As he traveled he noted fossil forms in rocks as well as the living forms in field and forest. He observed the correspondence in type between certain extinct forms and recent animals in South America. He noticed in the Galapagos Islands a fauna similar in general characteristics to that of the mainland, five or six hundred miles distant, and yet totally different as to species. Moreover, certain species were found to be confined to particular islands. These observations awakened in his mind, a mind naturally given to inquiring into the causes of things, questions that led to the formulation of his theory. It was not, however, until 1837 that he commenced his first note-book for containing his observations upon the transmutations of animals. He started as a firm believer in the fixity of species, and spent several years collecting and considering data before he changed his views.

At Downs.--On his return to England, after spending some time in London, he purchased a country-place at Downs, and, as his inheritance made it possible, he devoted himself entirely to his researches.

But, as is well known, he found in his illness a great obstacle to steady work. He had been a vigorous youth and young man, fond of outdoor sports, as fishing, shooting, and the like. After returning from his long voyage, he was affected by a form of constant illness, involving a giddiness in the head, and "for nearly forty years he never knew one day of the health of an ordinary man, and thus his life was one long struggle against the weariness and strain of sickness." Gould in his _Biographical Clinics_ attributes his illness to eye-strain.

"Under such conditions absolute regularity of routine was essential, and the day's work was carefully planned out. At his best, he had three periods of work: from 8.00 to 9.30; from 10.30 to 12.15; and from 4.30 to 6.00, each period being under two hours' duration."

The patient thoroughness of his experimental work and of his observation is shown by the fact that he did not publish his book on the _Origin of Species_ until he had worked on his theory twenty-two years. The circumstances that led to his publishing it when he did have already been indicated.

Parallelism in the Thought of Darwin and Wallace.--No one can read the letters of Darwin and Wallace explaining how they arrived at their idea of natural selection without marveling at the remarkable parallelism in the thought of the two. It is a noteworthy circumstance that the idea of natural selection came to both by the reading of the same book, _Malthus on Population_.

Darwin's statement of how he arrived at the conception of natural selection is as follows: "In October, 1838, that is, fifteen months after I had begun my systematic inquiry, I happened to read for amusement _Malthus on Population_, and being well prepared to appreciate the struggle for existence which everywhere goes on from long-continued observations of the habits of animals and plants, it at once struck me that under these circumstances favourable variations would tend to be preserved and unfavourable ones to be destroyed. _The result of this would be the formation of new species._ Here then I had at last got a theory by which to work, but I was so anxious to avoid prejudice that I determined not for some time to write even the briefest sketch of it. In June, 1842, I first allowed myself the satisfaction of writing a very brief abstract of my theory in pencil, in thirty-five pages, and this was enlarged during the summer of 1844 into one of 230 pages."

And Wallace gives this account: "In February, 1858, I was suffering from a rather severe attack of intermittent fever at Ternate, in the Moluccas; and one day, while lying on my bed during the cold fit, wrapped in blankets, though the thermometer was at 88° Fahr., the problem again presented itself to me, and something led me to think of the 'positive checks' described by Malthus in his _Essay on Population_, a work I had read several years before, and which had made a deep and permanent impression on my mind. These checks--war, disease, famine, and the like--must, it occurred to me, act on animals as well as man. Then I thought of the enormously rapid multiplication of animals, causing these checks to be much more effective in them than in the case of man; and while pondering vaguely on this fact, there suddenly flashed upon me the _idea_ of the survival of the fittest--that the individuals removed by these checks must be on the whole inferior to those that survived. In the two hours that elapsed before my ague fit was over, I had thought out almost the whole of the theory; and the same evening I sketched the draught of my paper, and in the two succeeding evenings wrote it out in full, and sent it by the next post to Mr. Darwin."

It thus appears that the announcement of the Darwin-Wallace theory of natural selection was made in 1858, and in the following year was published the book, the famous _Origin of Species_, upon which Darwin had been working when he received Mr. Wallace's essay. Darwin spoke of this work as an outline, a sort of introduction to other works that were in the course of preparation. His subsequent works upon _Animals and Plants under Domestication_, _The Descent of Man_, etc., etc., expanded his theory, but none of them effected so much stir in the intellectual world as the _Origin of Species_.

This skeleton outline should be filled out by reading _Darwin's Life and Letters_, by his son, and the complete papers of Darwin and Wallace, as originally published in the _Journal of the Linnæan Society_. The original papers are reproduced in the _Popular Science Monthly_ for November, 1901.

Wallace was born in 1823, and is still living. He shares with Darwin the credit of propounding the theory of natural selection, and he is notable also for the publication of important books, as the _Malay Archipelago_, _The Geographical Distribution of Animals_, _The Wonderful Century_, etc.

The Spread of the Doctrine of Organic Evolution. Huxley.--Darwin was of a quiet habit, not aggressive in the defense of his views. His theory provoked so much opposition that it needed some defenders of the pugnacious type. In England such a man was found in Thomas Henry Huxley (1825-1895). He was one of the greatest popular exponents of science of the nineteenth century; a man of most thorough and exact scholarship, with a keen, analytical mind that went directly to the center of questions under consideration, and powers as a writer that gave him a wide circle of readers. He was magnificently sincere in his fight for the prevalence of intellectual honesty. Doubtless he will be longer remembered for this service than for anything else.

He defended the doctrine of evolution, not only against oratorical attacks like that of Bishop Wilberforce, but against well-considered arguments and more worthy opponents. He advanced the standing of the theory in a less direct way by urging the pursuit of scientific studies by high-school and university students, and by bringing science closer to the people. He was a pioneer in the laboratory teaching of biology, and his _Manual_ has been, ever since its publication in 1874, the inspiration and the model for writers of directions for practical work in that field.

It is not so generally known that he was also a great investigator, producing a large amount of purely technical researches. After his death a memorial edition of his scientific memoirs was published in four large quarto volumes. The extent of his scientific output when thus assembled was a surprise to many of his co-workers in the field of science. His other writings of a more general character have been collected in fourteen quarto volumes. Some of the essays in this collection are models of clear and vigorous English style. Mr. Huxley did an astonishing amount of scientific work, especially in morphology and palæontology. Those who have been privileged to look over his manuscripts and unpublished drawings in his old room at South Kensington could not fail to have been impressed, not only with the extent, but also with the accuracy of his work. Taking Johannes Müller as his exemplar, he investigated animal organisms with a completeness and an exactness that have rarely been equaled.

An intimate account of his life will be found in _The Life and Letters of Thomas Henry Huxley_, by his son.

Haeckel.--Ernst Haeckel, of Jena, born in 1834 (Fig. 122), was one of the earliest in Germany to take up the defense of Darwin's hypothesis. As early as 1866 he applied the doctrine of evolution to all organisms in his _Generelle Morphologie_. This work, which has been long out of print, represents his best contribution to evolutionary thought. He has written widely for general readers, and although his writings are popularly believed to represent the best scientific thought on the matter, those written for the general public are not regarded by most biologists as strictly representative. As a thinker he is more careless than Huxley, and as a result less critical and exact as a writer.

There can be no doubt that the germs of evolutionary thought existed in Greek philosophy, and that they were retained in a state of low vitality among the mediæval thinkers who reflected upon the problem of creation. It was not, however, until the beginning of the nineteenth century that, under the nurture of Lamarck, they grew into what we may speak of as the modern theory of evolution. After various vicissitudes this doctrine was made fertile by Darwin, who supplied it with a new principle, that of natural selection.

The fruits of this long growth are now being gathered. After Darwin the problem of biology became not merely to describe phenomena, but to explain them. This is the outcome of the rise and progress of biology: first, crude and uncritical observations of the forms of animated nature; then descriptive analysis of their structure and development; and, finally, experimental studies, the effort to explain vital phenomena, an effort in which biologists are at present engaged.