CHAPTER XVII

THEORIES OF EVOLUTION: LAMARCK, DARWIN

The impression so generally entertained that the doctrine of organic evolution is a vague hypothesis, requiring for its support great stretches of the imagination, gives way to an examination of the facts, and we come to recognize that it is a well-founded theory, resting upon great accumulations of evidence. If the matter could rest here, it would be relatively simple; but it is necessary to examine into the causes of the evolutionary process. While scientific observation has shown that species are not fixed, but undergo transformations of considerable extent, there still remains to be accounted for the way in which these changes have been produced.

One may assume that the changes in animal life are the result of the interaction of protoplasm and certain natural agencies in its surroundings, but it is evidently a very difficult matter to designate the particular agencies or factors of evolution that have operated to bring about changes in species. The attempts to indicate these factors give rise to different theories of evolution, and it is just here that the controversies concerning the subject come in. We must remember, however, that to-day the controversies about evolution are not as to whether it was or was not the method of creation, but as to the factors by which the evolution of different forms was accomplished. Says Packard: "We are all evolutionists, though we may differ as to the nature of the efficient causes."

Of the various theories which had been advanced to account for evolution, up to the announcement of the mutation-theory of De Vries in 1900, three in particular had commanded the greatest amount of attention and been the field for varied and extensive discussion. These are the theories of Lamarck, Darwin, and Weismann. They are comprehensive theories, dealing with the process as a whole. Most of the others are concerned with details, and emphasize certain phases of the process.

Doubtless the factors that have played a part in molding the forms that have appeared in the procession of life upon our globe have been numerous, and, in addition to those that have been indicated, Osborn very aptly suggests that there may be undiscovered factors of evolution. Within a few years De Vries has brought into prominence the idea of sudden transformations leading to new species, and has accounted for organic evolution on that basis. Further consideration of this theory, however, will be postponed, while in the present chapter we shall endeavor to bring out the salient features of the theories of Lamarck and Darwin, without going into much detail regarding them.

Lamarck

Lamarck was the first to give a theory of evolution that has retained a place in the intellectual world up to the present time, and he may justly be regarded as the founder of that doctrine in the modern sense. The earlier theories were more restricted in their reach than that of Lamarck. Erasmus Darwin, his greatest predecessor in this field of thought, announced a comprehensive theory, which, while suggestive and forceful in originality, was diffuse, and is now only of historical importance. The more prominent writers on evolution in the period prior to Lamarck will be dealt with in the chapter on the Rise of Evolutionary Thought.

Lamarck was born in 1744, and led a quiet, monotonous life, almost pathetic on account of his struggles with poverty, and the lack of encouragement and proper recognition by his contemporaries. His life was rendered more bearable, however, even after he was overtaken by complete blindness, by the intellectual atmosphere that he created for himself, and by the superb confidence and affection of his devoted daughter Cornélie, who sustained him and made the truthful prediction that he would be recognized by posterity ("_La postérité vous honorera_").

His Family.--He came of a military family possessing some claims to distinction. The older name of the family had been de Monet, but in the branch to which Lamarck belonged the name had been changed to de Lamarque, and in the days of the first Republic was signed plain Lamarck by the subject of this sketch. Jean Baptiste Lamarck was the eleventh and last child of his parents. The other male members of the family having been provided with military occupations, Jean was selected by his father, although against the lad's own wish, for the clerical profession, and accordingly was placed in the college of the Jesuits at Amiens. He did not, however, develop a taste for theological studies, and after the death of his father in 1760 "nothing could induce the incipient abbé, then seventeen years of age, longer to wear his bands."

His ancestry asserted itself, and he forsook the college to follow the French army that was then campaigning in Germany. Mounted on a broken-down horse which he had succeeded in buying with his scanty means, he arrived on the scene of action, a veritable raw recruit, appearing before Colonel Lastic, to whom he had brought a letter of recommendation.

Military Experience.--The Colonel would have liked to be rid of him, but owing to Lamarck's persistence, assigned him to a company; and, being mounted, Lamarck took rank as a sergeant. During his first engagement his company was exposed to the direct fire of the enemy, and the officers one after another were shot until Lamarck by order of succession was in command of the fourteen remaining grenadiers. Although the French army retreated, Lamarck refused to move with his squad until he received directions from headquarters to retire. In this his first battle he showed the courage and the independence that characterized him in later years.

Adopts Natural Science.--An injury to the glands of the neck, resulting from being lifted by the head in sport by one of his comrades, unfitted him for military life, and he went to Paris and began the study of medicine, supporting himself in the mean time by working as a bank clerk. It was in his medical course of four years' severe study that Lamarck received the exact training that was needed to convert his enthusiastic love for science into the working powers of an investigator. He became especially interested in botany, and, after a chance interview with Rousseau, he determined to follow the ruling passion of his nature and devote himself to natural science. After about nine years' work he published, in 1778, his _Flora of France_, and in due course was appointed to a post in botany in the Academy of Sciences. He did not hold this position long, but left it to travel with the sons of Buffon as their instructor. This agreeable occupation extended over two years, and he then returned to Paris, and soon after was made keeper of the herbarium in the Royal Garden, a subordinate position entirely beneath his merits. Lamarck held this poorly paid position for several years, and was finally relieved by being appointed a professor in the newly established _Jardin des Plantes_.

He took an active part in the reorganization of the Royal Garden (_Jardin du Roi_) into the _Jardin des Plantes_. When, during the French Revolution, everything that was suggestive of royalty became obnoxious to the people, it was Lamarck who suggested in 1790 that the name of the King's Garden be changed to that of the Botanical Garden (_Jardin des Plantes_). The Royal Garden and the Cabinet of Natural History were combined, and in 1793 the name Jardin des Plantes proposed by Lamarck was adopted for the institution.

It was through the endorsements of Lamarck and Geoffroy Saint-Hilaire that Cuvier was brought into this great scientific institution; Cuvier, who was later to be advanced above him in the Jardin and in public favor, and who was to break friendship with Lamarck and become the opponent of his views, and who also was to engage in a memorable debate with his other supporter, Saint-Hilaire.

The portrait of Lamarck shown in Fig. 112 is one not generally known. Its date is undetermined, but since it was published in Thornton's _British Plants_ in 1805, we know that it was painted before the publication of Lamarck's _Philosophie Zoologique_, and before the full force of the coldness and heartless neglect of the world had been experienced. In his features we read supremacy of the intellect, and the unflinching moral courage for which he was notable. Lamarck has a more hopeful expression in this portrait than in those of his later years.

[Illustration: Fig. 112.--Lamarck, 1774-1829.

From Thornton's _British Plants_, 1805.]

Lamarck Changes from Botany to Zoölogy.--Until 1794, when he was fifty years of age, Lamarck was devoted to botany, but on being urged, after the reorganization of the _Jardin du Roi_, to take charge of the department of invertebrates, he finally consented and changed from the study of plants to that of animals. This change had profound influence in shaping his ideas. He found the invertebrates in great confusion, and set about to bring order out of chaos, an undertaking in which, to his credit be it acknowledged, he succeeded. The fruit of his labors, the Natural History of Invertebrated Animals (_Historie naturelle des Animaux sans Vertèbres_, 1815-1822), became a work of great importance. He took hold of this work, it should be remembered, as an expert observer, trained to rigid analysis by his previous critical studies in botany. In the progress of the work he was impressed with the differences in animals and the difficulty of separating one species from another. He had occasion to observe the variations produced in animals through the influence of climate, temperature, moisture, elevation above the sea-level, etc.

He observed also the effects of use and disuse upon the development of organs: the exercise of an organ leading to its greater development, and the disuse to its degeneration. Numerous illustrations are cited by Lamarck which serve to make his meaning clear. The long legs of wading birds are produced and extended by stretching to keep above the water; the long neck and bill of storks are produced by their habit of life; the long neck of the giraffe is due to reaching for foliage on trees; the web-footed birds, by spreading the toes when they strike the water, have stimulated the development of a membrane between the toes, etc. In the reverse direction, the loss of the power of flight in the "wingless" bird of New Zealand is due to disuse of the wings; while the loss of sight in the mole and in blind cave animals has arisen from lack of use of eyes.

The changes produced in animal organization in this way were believed to be continued by direct inheritance and improved in succeeding generations.

He believed also in a perfecting principle, tending to improve animals--a sort of conscious endeavor on the part of the animal playing a part in its better development. Finally, he came to believe that the agencies indicated above were the factors of the evolution of life.

His Theory of Evolution.--All that Lamarck had written before he changed from botany to zoölogy (1794) indicates his belief in the fixity of species, which was the prevailing notion among naturalists of the period. Then, in 1800, we find him apparently all at once expressing a contrary opinion, and an opinion to which he held unwaveringly to the close of his life. It would be of great interest to determine when Lamarck changed his views, and upon what this radical reversal of opinion was based; but we have no sure record to depend upon. Since his theory is developed chiefly upon considerations of animal life, it is reasonable to assume that his evolutionary ideas took form in his mind after he began the serious study of animals. Doubtless, his mind having been prepared and his insight sharpened by his earlier studies, his observations in a new field supplied the data which led him directly to the conviction that species are unstable. As Packard, one of his recent biographers, points out, the first expression of his new views of which we have any record occurred in the spring of 1800, on the occasion of his opening lecture to his course on the invertebrates. This avowal of belief in the extensive alteration of species was published in 1801 as the preface to his _Système des Animaux sans Vertèbres_. Here also he foreshadowed his theory of evolution, saying that nature, having formed the simplest organisms, "then with the aid of much time and favorable circumstances ... formed all the others." It has been generally believed that Lamarck's first public expression of his views on evolution was published in 1802 in his _Recherches sur l'Organisation des Corps Vivans_, but the researches of Packard and others have established the earlier date.

Lamarck continued for several years to modify and amplify the expression of his views. It is not necessary, however, to follow the molding of his ideas on evolution as expressed in the opening lectures to his course in the years 1800, 1802, 1803, and 1806, since we find them fully elaborated in his _Philosophie Zoologique_, published in 1809, and this may be accepted as the standard source for the study of his theory. In this work he states two propositions under the name of laws, which have been translated by Packard as follows:

"_First Law_: In every animal which has not exceeded the term of its development, the more frequent and sustained use of any organ gradually strengthens this organ, develops and enlarges it, and gives it a strength proportioned to the length of time of such use; while the constant lack of use of such an organ imperceptibly weakens it, causing it to become reduced, progressively diminishes its faculties, and ends in its disappearance.

"_Second Law_: Everything which nature has caused individuals to acquire or lose by the influence of the circumstances to which their race may be for a long time exposed, and consequently by the influence of the predominant use of such an organ, or by that of the constant lack of use of such part, it preserves by heredity and passes on to the new individuals which descend from it, provided that the changes thus acquired are common to both sexes, or to those which have given origin to these new individuals.

"These are the two fundamental truths which can be misunderstood only by those who have never observed or followed nature in its operations," etc. The first law embodies the principle of use and disuse, the second law that of heredity.

In 1815 his theory received some extensions of minor importance. The only points to which attention need be called are that he gives four laws instead of two, and that a new feature occurs in the second law in the statement that the production of a new organ is the result of a new need (_besoin_) which continues to make itself felt.

Simplified Statement of Lamarck's Views.--For practical exposition the theory maybe simplified into two sets of facts: First, those to be classed under variation; and, second, those under heredity. Variations of organs, according to Lamarck, arise in animals mainly through use and disuse, and new organs have their origin in a physiological need. A new need felt by the animal expresses itself on the organism, stimulating growth and adaptations in a particular direction. This part of Lamarck's theory has been subjected to much ridicule. The sense in which he employs the word _besoin_ has been much misunderstood; when, however, we take into account that he uses it, not merely as expressing a wish or desire on the part of the animal, but as the reflex

## action arising from new conditions, his statement loses its alleged

grotesqueness and seems to be founded on sound physiology.

Inheritance.--Lamarck's view of heredity was uncritical; according to his conception, inheritance was a simple, direct transmission of those superficial changes that arise in organs within the lifetime of an individual owing to use and disuse. It is on this question of the direct inheritance of variations acquired in the lifetime of an individual that his theory has been the most assailed. The belief in the inheritance of acquired characteristics has been so undermined by experimental evidence that at the present time we can not point to a single unchallenged instance of such inheritance. But, while Lamarck's theory has shown weakness on that side, his ideas regarding the production of variations have been revived and extended.

Variation.--The more commendable part of his theory is the attempt to account for variation. Darwin assumed variation, but Lamarck attempted to account for it, and in this feature many discerning students maintain that the theory of Lamarck is more philosophical in its foundation than that of Darwin.

In any theory of evolution we must deal with the variation of organisms and heredity, and thus we observe that the two factors discussed by Lamarck are basal. Although it must be admitted that even to-day we know little about either variation or heredity, they remain basal factors in any theory of evolution.

Time and Favorable Conditions.--Lamarck supposed a very long time was necessary to bring about the changes which have taken place in animals. The central thought of time and favorable conditions occurs again and again in his writings. The following quotation is interesting as coming from the first announcement of his views in 1800:

"It appears, as I have already said, that _time_ and _favorable conditions_ are the two principal means which nature has employed in giving existence to all her productions. We know that for her time has no limit, and that consequently she has it always at her disposal.

"As to the circumstances of which she has had need and of which she makes use every day in order to cause her productions to vary, we can say that in a manner they are inexhaustible.

"The essential ones arising from the influence and from all the environing media, from the diversity of local causes, of habits, of movements, of action, finally of means of living, of preserving their lives, of defending themselves, of multiplying themselves, etc. Moreover, as the result of these different influences, the faculties, developed and strengthened by use, become diversified by the new habits maintained for long ages, and by slow degrees the structure, the consistence--in a word, the nature, the condition of the parts and of the organs consequently participating in all these influences, became preserved and were propagated by heredity (génération)." (Packard's translation.)

Salient Points.--The salient points in Lamarck's theory may be compacted into a single sentence: It is a theory of the evolution of animal life, depending upon variations brought about mainly through use and disuse of parts, and also by responses to external stimuli, and the direct inheritance of the same. His theory is comprehensive, so much so that he includes mankind in his general conclusions.

Lamarck supposed that an animal having become adapted to its surroundings would remain relatively stable as to its structure. To the objection raised by Cuvier that animals from Egypt had not changed since the days when they were preserved as mummies, he replied that the climate of Egypt had remained constant for centuries, and therefore no change in its fauna was to be expected.

Species.--Since the question of the fixity of species is the central one in theories of evolution, it will be worth while to quote Lamarck's definition of species: "All those who have had much to do with the study of natural history know that naturalists at the present day are extremely embarrassed in defining what they mean by the word species.... We call _species_ every collection of individuals which are alike or almost so, and we remark that the regeneration of these individuals conserves the species and propagates it in continuing successively to reproduce similar individuals." He then goes on with a long discussion to show that large collections of animals exhibit a great variation in species, and that they have no absolute stability, but "enjoy only a relative stability."

Herbert Spencer adopted and elaborated the theory of Lamarck. He freed it from some of its chief crudities, such as the idea of an innate tendency toward perfection. In many controversies Mr. Spencer defended the idea of the transmission of acquired characters. The ideas of Lamarck have, therefore, been transmitted to us largely in the Spencerian mold and in the characteristic language of that great philosopher. There has been but little tendency to go to Lamarck's original writings. Packard, whose biography of Lamarck appeared in 1901, has made a thorough analysis of his, writings and had incidentally corrected several erroneous conception.

Neo-Lamarckism.--The ideas of Lamarck regarding the beginning of variations have been revived and accorded much respect under the designation of Neo-Lamarckism. The revival of Lamarckism is especially owing to the palæontological investigations of Cope and Hyatt. The work of E.D. Cope in particular led him to attach importance to the effect of mechanical and other external causes in producing variation, and he points out many instances of use-inheritance. Neo-Lamarckism has a considerable following; it is a revival of the fundamental ideas of Lamarck.

Darwin's Theory

While Lamarck's theory rests upon two sets of facts, Darwin's is founded on three: _viz._, the facts of variation, of inheritance, and of natural selection. The central feature of his theory is the idea of natural selection. No one else save Wallace had seized upon this feature when Darwin made it the center of his system. On account of the part taken by Wallace simultaneously with Darwin in announcing natural selection as the chief factor of evolution, it is appropriate to designate this contribution as the Darwin-Wallace principle of natural selection. The interesting connection between the original conclusions of Darwin and Wallace is set forth in