“We do not here have to do with a line of argument, but with the examination of a positive fact, which is more general than is supposed, and whichhas not received the attention it deserves, doubtless because, very often, it is quite difficult to discover. This fact consists in the influence which circumstances exert on the different organisms subjected to them.“In truth, for a long time there has been noticed the influence of different states of our organization on our character, our propensities (penchants), our actions, and even our ideas; but it seems to me that no one has yet recognized that of our actions and of our habits on our organization itself. Now, as these actions and these habits entirely depend on the circumstances in which we habitually find ourselves, I shall try to show how great is the influence which these circumstances exercise on the general form, on the condition of the parts, and even on the organization of living bodies. It is therefore this very positive fact which is to be the subject of this chapter.“If we have not had numerous occasions to plainly recognize the effects of this influence on certain organisms which we have transported under entirely new and different circumstances, and if we had not seen these effects and the changes resulting from them produced, in a way, under our very eyes, the important fact in question would have always remained unknown.“The influence of circumstances is really continuously and everywhere active on living beings, but what renders it difficult for us to appreciate this influence is that its effects only become sensible or recognizable (especially in the animals) at the end of a long period.“Before stating and examining the proofs of this fact, which deserves our attention, and which is very important for a zoölogical philosophy, let us resume the thread of the considerations we had begun to discuss.“In the preceding paragraph we have seen that it is now an incontrovertible fact that, in consideringthe animal scale in a sense the inverse of that of nature, we find that there exists in the groups composing this scale a continuous but irregular modification (dégradation) in the organization of animals which they comprise, an increasing simplification in the organization of these organisms; finally, a proportionate diminution in the number of faculties of these beings.“This fact once recognized may throw the greatest light on the very order which nature has followed in the production of all the existing animals; but it does not show why the structure of animals in its increasing complexity from the more imperfect up to the most perfect offers only an irregular gradation, whose extent presents a number of anomalies or digressions which have no appearance of order in their diversity.“Now, in seeking for the reason of this singular irregularity in the increasing complexity of organization of animals, if we should consider the outcome of the influences that the infinitely diversified circumstances in all parts of the globe exercise on the general form, the parts, and the very organization of these animals, everything will be clearly explained.“It will, indeed, be evident that the condition in which we find all animals is, on one side, the result of the increasing complexity of the organization which tends to form a regular gradation, and, on the other, that it is that of the influences of a multitude of very different circumstances which continually tend to destroy the regularity in the gradations of the increasing complexity of the organization.“Here it becomes necessary for me to explain the meaning I attach to the expressioncircumstances influencing the form and structure of animals—namely, that in becoming very different they change, with time, both their form and organization by proportionate modifications.“Assuredly, if these expressions should be taken literally, I should be accused of an error; for whatever may be the circumstances, they do not directly cause any modification in the form and structure of animals.“But the great changes in the circumstances bring about in animals great changes in their needs, and such changes in their needs necessarily cause changes in their actions. Now, if the new needs become constant or very permanent, the animals then assume newhabits, which are as durable as the needs which gave origin to them. We see that this is easily demonstrated and even does not need any explanation to make it clearer.“It is then evident that a great change in circumstances having become constant in a race of animals leads these animals into new habits.“Now, if new circumstances, having become permanent in a race of animals, have given to these animals newhabits—that is to say, have led them to perform new actions which have become habitual—there will from this result the use of such a part by preference to that of another, and in certain cases the total lack of use of any part which has become useless.“Nothing of all this should be considered as a hypothesis or as a mere peculiar opinion; they are, on the contrary, truths which require, in order to be made evident, only attention to and the observation of facts.“We shall see presently by the citation of known facts which prove it, on one side that the new wants, having rendered such a part necessary, have really by the result of efforts given origin to this part, and that as the result of its sustained use it has gradually strengthened it, developed, and has ended in considerably increasing its size; on the other side we shall see that, in certain cases, the new circumstancesand new wants having rendered such a part wholly useless, the total lack of use of this part has led to the result that it has gradually ceased to receive the development which the other parts of the animal obtain; that it gradually becomes emaciated and thin; and that finally, when this lack of use has been total during a long time, the part in question ends in disappearing. All this is a positive fact; I propose to give the most convincing proofs.“In the plants, where there are no movements, and, consequently, no habits properly so called, great changes in circumstances do not bring about less great differences in the development of their parts; so that these differences originate and develop certain of them, while they reduce and cause several others to disappear. But here everything operates by the changes occurring in the nutrition of the plant, in its absorptions and transpirations, in the amount of heat, light, air, and humidity which it habitually receives; finally, in the superiority that certain of the different vital movements may assume over others.“Between individuals of the same species, some of which are constantly well nourished, and in circumstances favorable to their entire development, while the others live under reversed circumstances, there is brought about a difference in the condition of these individuals which gradually becomes very remarkable. How many examples could I not cite regarding animals and plants, which would confirm the grounds for this view! Now, if the circumstances remain the same, rendering habitual and constant the condition of individuals badly fed, diseased, or languishing, their internal organization becomes finally modified, and reproduction between the individuals in question preserves the acquired modifications, and ends in giving rise to a race very distinct from that of the individuals which unceasingly meet with circumstances favorable to their development.“A very dry spring-time is the cause of the grass of a field growing very slowly, remaining scraggy and puny, flowering and fruiting without growing much.“A spring interspersed with warm days and rainy days makes the same grass grow rapidly, and the harvest of hay is then excellent.“But if any cause perpetuates the unfavorable circumstances surrounding these plants, they vary proportionally, at first in their appearance and general condition, and finally in several particulars of their characters.“For example, if some seed of any of the grasses referred to should be carried into an elevated place, on a dry and stony greensward much exposed to the winds, and should germinate there, the plant which should be able to live in this place would always be badly nourished, and the individuals reproduced there continuing to exist under these depressing circumstances, there would result a race truly different from that living in the field, though originating from it. The individuals of this new race would be small, scraggy, and some of their organs, having developed more than others, would then offer special proportions.“Those who have observed much, and who have consulted the great collections, have become convinced that in proportion as the circumstances of habitat, exposure, climate, food, mode of life, etc., come to change, the characters of size, form, proportion between the parts, color, consistence, agility, and industry in the animals change proportionally.“What nature accomplishes after a long time, we bring about every day by suddenly changing, in the case of a living plant, the circumstances under which it and all the individuals of its species exist.“All botanists know that the plants which they transplant from their birthplace into gardens for cultivation gradually undergo changes which at last render them unrecognizable. Many plants naturallyvery hairy then become glabrous, or almost so; many of those which were creeping and trailing, then become erect; others lose their spines or their prickles; others still, from the woody and perennial condition which their stem possesses in a warm climate, pass, in our climate, into an herbaceous condition, and among these several are nothing more than annual plants; finally, the dimensions of their parts themselves undergo very considerable changes. These effects of changes of circumstances are so well known that botanists prefer not to describe garden plants, at least only those which have been newly cultivated.“Is not cultivated wheat (Triticum sativum) only a plant brought by man into the condition in which we actually see it? Who can tell me in what country such a plant lives in a state of nature—that is to say, without being there the result of its culture in some neighboring region?“Where occur in nature our cabbage, lettuce, etc., in the condition in which we see them in our kitchen-gardens? Is it not the same as regards a number of animals which domestication has changed or considerably modified?“What very different races among our fowls and domestic pigeons, which we have obtained by raising them in different circumstances and in different countries, and how vainly do we now endeavor to rediscover them in nature!“Those which are the least changed, without doubt by a more recent process of domestication, and because they do not live in a climate which is foreign to them, do not the less possess, in the condition of some of their parts, great differences produced by the habits which we have made them contract. Thus our ducks and our domestic geese trace back their type to the wild ducks and geese; but ours have lost the power of rising into the high regions of the air, and of flying over extensive regions; finally, a decidedchange has been wrought in the state of their parts compared with that of animals of the race from which they have descended.“Who does not know that such a native bird, which we raise in a cage and which lives there five or six years in succession, and after that replaced in nature—namely, set free—is then unable to fly like its fellows which have always been free? The slight change of circumstance operating on this individual has only diminished its power of flight, and doubtless has not produced any change in the shape of its parts. But if a numerous series of generations of individuals of the same race should have been kept in captivity for a considerable time, there is no doubt but that even the form of the parts of these individuals would gradually undergo notable changes. For a much stronger reason, if, instead of a simple captivity constantly maintained over them, this circumstance had been at the same time accompanied by a change to a very different climate, and if these individuals by degrees had been habituated to other kinds of food, and to other kinds of movements to obtain it; certainly these circumstances, united and becoming constant, would insensibly form a new and special race.“Where do we find, in nature, this multitude of races ofdogs, which, as the result of domesticity to which we have reduced these animals, have been brought into their present condition? Where do we find these bull-dogs, greyhounds, water spaniels, spaniels, pug-dogs, etc., etc., races which present among themselves much greater differences than those which we admit to be specific in wild animals of the same genus?“Without doubt, a primitive single race, very near the wolf, if it is not itself the true type, has been submitted by man, at some period, to the process of domestication. This race, which then offered no difference between its individuals, has been graduallydispersed by man into different countries, with different climates; and after a time these same individuals, having undergone the influences of their habitats, and of the different habits they were obliged to contract in each country, have undergone remarkable changes, and have formed different special races. Now, the man who, for commercial reasons or from interests of any other kind, travels a very great distance, having carried into a densely populated place, as for example a great capital, different races of dogs originated in some very distant country, then the increase of these races by heredity (génération) has given rise successively to all those we now know.“The following fact proves, as regards plants, how a change in any important circumstance leads to a change in the parts of their organisms.“So long asRanunculus aquatilisis submerged in the water, its leaves are all finely incised and the divisions hair-like; but when the stalks of this plant reach the surface of the water, the leaves which grow out in the air are wider, rounded, and simply lobed. If some feet from the same plant the roots succeed in pushing into a soil only damp, without being submerged, their stalks then are short, none of their leaves are divided into capillary divisions, which gives rise toRanunculus hederaceus, which the botanists regard as a species whenever they meet with it.“There is no doubt that as regards animals important changes in the circumstances under which they are accustomed to live do not produce alteration in their organs; for here the changes are much slower in operating than in plants, and, consequently, are to us less marked, and their cause less recognizable.“As to the circumstances which have so much power in modifying the organs of living beings, the most influential are, doubtless, the diversity of the surroundings in which they live; but besides thisthere are many others which, in addition, have a considerable influence in the production of the effects in question.“It is known that different localities change in nature and quality owing to their position, their nature, and their climate, as is easily seen in passing over different places distinguished by special features; hence we see a cause of variation for the animals and plants which live in these different places. But what we do not sufficiently know, and even what we generally refuse to believe, is that each place itself changes with time in exposure, in climate, in nature, and quality, although with a slowness so great in relation to our own continuance that we attribute to it a perfect stability.“Now, in either case, these changed localities proportionally change the circumstances relative to the organisms which inhabit them, and the latter then give rise to other influences bearing on these same beings.“We perceive from this that, if there are extremes in these changes, there are also gradations—namely, degrees which are intermediate and which fill the interval. Consequently there are also gradations in the differences which distinguish what we callspecies.“It is then evident that the whole surface of the earth offers, in the nature and situation of the matters which occupy its different points, a diversity of circumstances which is throughout in relation with that of the forms and parts of animals, independent of the special diversity which necessarily results from the progress of the composition of organization in each animal.“In each locality where animals can live, the circumstances which establish there an order of things remain for a long time the same, and really change there only with a slowness so great that man cannot directly notice them. He is obliged to consultmonuments to recognize that in each one of these places the order of things that he discovers there has not always been the same, and to perceive that it will change more.“The races of animals which live in each of these places should, then, retain their customary habits there also for a long time; hence to us seems an apparent constancy of races which we callspecies—constancy which has originated among us the idea that these races are as ancient as nature.“But in the different points of the earth’s surface which can be inhabited, nature and the situation of the places and climates constitute there, for the animals as for the plants,different circumstancesof all sorts of degrees. The animals which inhabit these different places should then differ from each other, not only on account of the state of nature of the organization in each race, but, besides, by reason of the habits that the individuals of each race there are forced to have; so, in proportion as he traverses the larger parts of the earth’s surface the observing naturalist sees circumstances changing in a manner somewhat noticeable; he constantly sees that the species change proportionately in their characters.“Now, the true order of things necessary to consider in all this consists in recognizing:“1. That every slight change maintained under the circumstances where occur each race of animals, brings about in them a real change in their wants.“2. That every change in the wants of animals necessitates in them other movements (actions) to satisfy the new needs, and consequently other habits.“3. That every new want necessitating new actions to satisfy it, demands of the animal which feels it both the more frequent use of such of its parts of which before it made less use, which develops and considerably enlarges them, and the use of new parts which necessity has caused to insensibly develop in it bythe effects of its inner feelings; which I shall constantly prove by known facts.“Thus, to arrive at a knowledge of the true causes of so many different forms and so many different habits of which the known animals offer us examples, it is necessary to consider that circumstances infinitely diversified, but all slowly changing, into which the animals of each race are successively thrown, have caused, for each of them, new wants and necessarily changes in their habits. Moreover, this truth, which cannot be denied, being once recognized, it will be easy to see how the new needs have been able to be satisfied, and the new habits formed, if any attention be given to the two following laws of nature, which observation always confirms:“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, causes 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 (génération) and passes on to the new individuals which descend from it, provided that the changes thus acquired are common to both sexes, orto 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, or only by those who allow themselves to fall into the error which I have combated.“Naturalists having observed that the forms of the parts of animals compared with the uses of these parts are always in perfect accord, have thought that the forms and conditions of parts have caused the function; but this is a mistake, for it is easy to demonstrate by observation that it is, on the contrary, the needs and uses of organs which have developed these same parts, which have even given origin to them where they did not exist, and which consequently have given rise to the condition in which we observe them in each animal.“If this were not so, it would have been necessary for nature to have created for the parts of animals as many forms as the diversity of circumstances in which they have to live had required, and that these forms and also the circumstances had never varied.“This is certainly not the existing order of things, and if it were really such, we should not have the race-horses of England; we should not have our great draft horses, so clumsy and so different from the first named, for nature herself has not produced their like; we should not, for the same reason, have terrier dogs with bow legs, greyhounds so swift in running, water-spaniels, etc.; we should not have tailless fowls, fantail pigeons, etc.; finally, we could cultivate the wild plants as much as we pleased in the rich and fertile soil of our gardens without fearing to see them change by long culture.“For a long time we have felt the force of the saying which has passed into the well-known proverb—habits form a second nature.“Assuredly, if the habits and nature of each animal can never vary, the proverb is false, has no foundation, and does not apply to the instances which led to its being spoken.“If we should seriously consider all that I have just stated, it might be thought that I had good reason when in my work entitledRecherches sur les Corps vivans(p. 50) I established the following proposition:“‘It is not the organs—that is to say, the nature and form of the parts of the body of an animal—which have given rise to its habits and its special faculties; but it is, on the contrary, its habits, its manner of life, and the circumstances in which are placed the individuals from which it originates, which have, with time, brought about the form of its body, the number and condition of its organs, finally, the faculties which it enjoys.’“If we weigh this proposition, and if we recall all the observations which nature and the state of things continually lead us to do, then its importance and its solidity will become more evident.“Time and favorable circumstances are, as I have already said, the two principal means which nature employs to give existence to all her productions: we know that time for her has no limits, and that consequently it is ever at her disposal.“As to the circumstances of which she has need, and which she uses still daily to cause variations in all that she continues to produce, we can say that they are, in some degree, for her inexhaustible.“The principal circumstances arise from the influence of climate; from those of different temperatures of the atmosphere, and from all the environing media; from that of the diversity of different localities and their situation; from that of habits, the ordinary movements, the most frequent actions; finally, from that of means of preservation, of mode of living, of defence, of reproduction, etc.“Moreover, owing to these diverse influences, the faculties increase and become stronger by use, become differentiated by the new habits preserved for long ages, and insensibly the organization, the consistence—in a word, the nature and condition of parts, as also of the organs—participate in the results of all these influences, become preserved, and are propagated by generation.“These truths, which are only the results of the two natural laws above stated, are in every case completely confirmed by facts; they clearly indicate the course of nature in all the diversity of its products.“But instead of contenting ourselves with generalities which might be considered as hypothetical, let us directly examine the facts, and consider, in the animals, the result of the use or disuse of their organs on the organs themselves, according to the habits that each race has been compelled to contract.“I shall now attempt to prove that the constant lack of exercise of organs at first diminishes their faculties, gradually impoverishes them, and ends by making them disappear, or even causing them to be atrophied, if this lack of use is perpetuated for a very long time through successive generations of animals of the same race.“I shall next prove that, on the contrary, the habit of exercising an organ, in every animal which has not attained the limit of the diminution of its faculties, not only perfects and increases the faculties of this organ, but, besides, enables it to acquire developments and dimensions which insensibly change it; so that with time it renders it very different from the same organ in another animal which exercises it much less.“The lack of use of an organ, become constant by the habits formed, gradually impoverishes this organ, and ends by causing it to disappear and even to destroy it.“As such a proposition can only be admitted on proof, and not by its simple announcement, let usprove it by the citation of the leading known facts on which it is based.“The vertebrate animals, whose plan of organization is in all nearly the same, although they offer much diversity in their parts, have jaws armed withteeth; moreover, those among them which circumstances have placed in the habit of swallowing their food without previousmasticationare exposed to the result that their teeth become undeveloped. These teeth, then, either remain concealed between the bony edges of the jaws, without appearing above, or even their gums are found to have been atrophied.“In the baleen whales, which have been supposed to be completely deprived of teeth, M. Geoffroy has found them concealed in the jaws of thefœtusof this animal. This professor has also found in the birds the groove where the teeth should be situated; but they are no longer to be seen there.“In the class even of mammals, which comprises the most perfect animals, and chiefly those in which the vertebrate plan of organization is most perfectly carried out, not only the baleen has no usable teeth, but the ant-eater (Myrmecophaga) is also in the same condition, whose habit of not masticating its food has been for a long time established and preserved in its race.“The presence of eyes in the head is a characteristic of a great number of different animals, and becomes an essential part of the plan of organization of vertebrates.“Nevertheless the mole, which owing to its habits makes very little use of vision, has only very small eyes, which are scarcely visible, since they exercise these organs to a very slight extent.“TheAspalaxof Olivier (Voyage en Egypte et en Perse, ii. pl. 28 f. 2), which lives under ground like the mole, and which probably exposes itself still less than that animal to the light of day, has totally lost thepower of sight; also it possesses only vestiges of the organ of which it is the seat; and yet these vestiges are wholly concealed under the skin and other parts which cover them, and do not permit the least access to the light.“TheProteus, an aquatic reptile allied to the salamander in its structure, and which lives in the dark subterranean waters of deep caves, has, like theAspalax, only vestiges of the organs of sight—vestiges which are covered and concealed in the same manner.“We turn to a decisive consideration relative to this question.“Light does not penetrate everywhere; consequently animals which habitually live in situations where it does not penetrate lack the occasion of exercising the organs of sight, if nature has provided them with them. Moreover, the animals which make part of the plan of organization in whicheyesare necessarily present, have originally had them. However, since we find them among those which are deprived of the use of this organ, and which have only vestiges concealed and covered over, it should be evident that the impoverishment and even the disappearance of these organs are the result of a constant lack of exercise.“What proves it is that the organ ofhearingis never in this condition, and that we always find it in the animals when the nature of their organization should require its existence; the reason is as follows.“Thecause of sound, that which, moved by the shock or the vibrations of bodies, transmits to the organ of hearing the impression which it receives, penetrates everywhere, traverses all the media, and even the mass of the densest bodies: from this it results that every animal which makes a part of a plan of organization to whichhearingis essential, has always occasion to exercise this organ in whatever situation it lives. So, among thevertebrate animalswe see none deprived of their organs of hearing; but in the groups below them, when the same organs are once wanting, we do not again find them.“It is not so with the organ of sight, for we see this organ disappear, reappear, and again disappear, in proportion to the possibility or impossibility of the animal’s exercising it.“In theacephalous molluscs, the great development of the mantle of these molluscs has rendered their eyes and even their head entirely useless. These organs, also forming a part of a plan of organization which should comprise them, have disappeared and atrophied from constant lack of use.“Finally, it is a part of the plan of organization ofreptiles, as in other vertebrate animals, to have four legs appended to their skeleton. The serpents should consequently have four, though they do not form the lowest order of reptiles, and are not so near the fishes as the batrachians (the frogs, the salamanders, etc.).“However, the serpents having taken up the habit of gliding along the ground, and of concealing themselves in the grass, their body, owing to continually repeated efforts to elongate itself so as to pass through narrow spaces, has acquired a considerable length disproportionate to its size. Moreover, limbs would have been very useless to these animals, and consequently would not have been employed: because long legs would have interfered with their need of gliding, and very short legs, not being more than four in number, would have been incapable of moving their body. Hence the lack of use of these parts having been constant in the races of these animals, has caused the total disappearance of these same parts, although really included in the plan of organization of the animals of their class.“Many insects which by the natural character of their order, and even of their genus, should have wings, lack them more or less completely fromdisuse. A quantity of Coleoptera, Orthoptera, Hymenoptera, and of Hemiptera, etc., afford examples; the habits of these animals do not require them to make use of their wings.“But it is not sufficient to give the explanation of the cause which has brought about the condition of the organs of different animals—a condition which we see to be always the same in those of the same species; we must besides observe the changes of condition produced in the organs of one and the same individual during its life, by the single result of a great change in the special habits in the individuals of its species. The following fact, which is one of the most remarkable, will serve to prove the influence of habits on the condition of organs, and show how changes wrought in the habits of an individual, produce the condition of the organs which are brought into action during the exercise of these habits.“M. Tenon, member of the Institute, has given an account to the Class of Sciences, that having examined the intestinal canal of several men who had been hard drinkers all their lives, he had constantly found it to be shortened to an extraordinary extent, compared with the same organ in those not given to such a habit.“We know that hard drinkers, or those who are addicted to drunkenness, take very little solid food, that they eat very lightly, and that the beverage which they take in excess frequently suffices to nourish them.“Moreover, as fluid aliments, especially spirituous liquors, do not remain a long time either in the stomach or in the intestines, the stomach and the remainder of the intestinal canal lose the habit of being distended in intemperate persons, so also in sedentary persons and those engaged in mental labor, who are habituated to take but little food. Gradually and at length their stomach becomes contracted, and their intestines shortened.“We are not concerned here with the shrinkage and shortening produced by a puckering of the parts, which permit ordinary extension, if instead of a continued emptiness these viscera should be filled; the shrinkage and shortening in question are real, considerable, and such that these organs would burst open rather than yield suddenly to the causes which would require ordinary extension.“In circumstances of persons of the same age, compare a man who, in order to devote himself to habitual study and mental work, which have rendered his digestion more difficult, has contracted the habit of eating lightly, with another who habitually takes a good deal of exercise, walks out often, and eats heartily; the stomach of the first will be weakened, and a small quantity of food will fill it, while that of the second will be not only maintained in its ordinary health but even strengthened.“We have here the case of an organ much modified in its dimensions and in its faculties by the single cause of a change in habits during the life of the individual.“The frequent use of an organ become constant by habit increases the faculties of this organ, even develops it, and enables it to acquire dimensions and a power of action which it does not possess in animals which exercise less.“We have just said that the lack of employment of an organ which necessarily exists modifies it, impoverishes it, and ends by its disappearing entirely.“I shall now demonstrate that the continued employment of an organ, with the efforts made to draw out its powers under circumstances where it would be of service, strengthens, extends, and enlarges this organ, or creates a new one which can exercise the necessary functions.“The bird which necessity drives to the water to find there prey fitted for its sustenance, opens the digits ofits feet when it wishes to strike the water and propel itself along its surface. The skin which unites these digits at their base, by these acts of spreading apart being unceasingly repeated contracts the habit of extending; so that after a while the broad membranes which connect the digits of ducks, geese, etc., are formed as we see them. The same efforts made in swimming—i.e., in pushing back the water, in order to advance and to move in this liquid—have likewise extended the membrane situated between the digits of the frogs, the sea-turtles, the otter, beaver, etc.“On the contrary, the bird whose mode of life habituates it to perch on trees, and which is born of individuals who have all contracted this habit, has necessarily the digits of the feet longer and shaped in another way than those of the aquatic animals which I have just mentioned. Its claws, after a while, became elongated, pointed, and curved or hook-like in order to grasp the branches on which the animal often rests.“Likewise we see that the shore bird, which is not inclined to swim, and which moreover has need of approaching the edge of the water to find there its prey, is in continual danger of sinking in the mud. Now, this bird, wishing to act so that its body shall not fall into the water, makes every effort to extend and elongate its legs. It results from this that the long-continued habit that this bird and the others of its race contract, of extending and continually elongating their legs, is thecauseof the individuals of this race being raised as if on stilts, having gradually acquired long, naked legs, which are denuded of feathers up to the thighs and often above them (Système des Animaux sans Vertèbres, p. 16).“We also perceive that the same bird, wishing to catch fish without wetting its body, is obliged to make continual efforts to lengthen its neck. Now, the results of these habitual efforts in this individualand in those of its race have enabled them, after a time, to singularly elongate them—as, indeed, is proved by the long neck of all shore birds.“If any swimming birds, such as the swan and the goose, whose legs are short, nevertheless have a very long neck, it is because these birds in swimming on the surface of the water have the habit of plunging their head down as far as they can, to catch aquatic larvæ and different animalcules for food, and because they make no effort to lengthen their legs.“When an animal to satisfy its wants makes repeated efforts to elongate its tongue, it will acquire a considerable length (the ant-eater, green wood-pecker); when it is obliged to seize anything with this same organ, then its tongue will divide and become forked. That of the humming-birds, which seize with their tongue, and that of the lizard and serpents, which use it to feel and examine objects in front of them, are proofs of what I advocate.“Wants, always occasioned by circumstances, and followed by sustained efforts to satisfy them, are not limited in results, in modifying—that is to say, in increasing or diminishing—the extent and the faculties of organs; but they also come to displace these same organs when certain of these wants become a necessity.“The fishes which habitually swim in large bodies of water, having need of seeing laterally, have, in fact, their eyes placed on the sides of the head. Their bodies, more or less flattened according to thespecies, have their sides perpendicular to the plane of the water, and their eyes are placed in such a way that there is an eye on each flattened side. But those fishes whose habits place them under the necessity of constantly approaching the shores, and especially the shelving banks or where the slope is slight, have been forced to swim on their flattened faces, so as to be ableto approach nearer the edge of the water. In this situation, receiving more light from above than from beneath, and having a special need of being always attentive to what is going on above them, this need has forced one of their eyes to undergo a kind of displacement, and to assume the very singular situation which is familiar to us in thesoles,turbots,dabs, etc. (PleuronectesandAchirus). The situation of these eyes is asymmetrical, because this results from an incomplete change. Now, this change is entirely completed in the rays, where the transverse flattening of the body is entirely horizontal, as also the head. Also the eyes of the rays, both situated on the upper side, have become symmetrical.“The serpents which glide along the surface of the ground are obliged chiefly to see elevated objects, or what are above their eyes. This necessity has brought an influence to bear on the situation of the organs of vision in these animals; and, in fact, they have the eyes placed in the lateral and upper parts of the head, so as to easily perceive what is above or at their sides; but they only see for a short distance what is in front of them. Moreover, forced to supply the lack of ability to see and recognize what is in front of their head, and which might injure them, they need only to feel such objects with the aid of their tongue, which they are obliged to dart out with all their power. This habit has not only contributed to render the tongue slender, very long and retractile, but has also led in a great number of species to its division, so as to enable them to feel several objects at once; it has likewise allowed them to form an opening at the end of their head, to enable the tongue to dart out without their being obliged to open their jaws.“Nothing is more remarkable than the result of habits in the herbivorous mammals.“The quadruped to whom circumstances and thewants which they have created have given for a long period, as also to others of its race, the habit of browsing on grass, only walks on the ground, and is obliged to rest there on its four feet the greater part of its life, moving about very little, or only to a moderate extent. The considerable time which this sort of creature is obliged to spend each day to fill itself with the only kind of food which it requires, leads it to move about very little, so that it uses its legs only to stand on the ground, to walk, or run, and they never serve to seize hold of or to climb trees.“From this habit of daily consuming great amounts of food which distend the organs which receive it, and of only moving about to a limited extent, it has resulted that the bodies of these animals are thick, clumsy, and massive, and have acquired a very great volume, as we see in elephants, rhinoceroses, oxen, buffaloes, horses, etc.“The habit of standing upright on their four feet during the greater part of the day to browse has given origin to a thick hoof which envelops the extremity of the digits of their feet; and as their toes are not trained to make any movement, and because they have served no other use than as supports, as also the rest of the leg, the most of them are short, are reduced in size, and even have ended by totally disappearing. Thus in thepachyderms, some have five toes enveloped in horn, and consequently their foot is divided into five parts; others have only four, and still others only three. But in theruminants, which seem to be the most ancient of mammals, which are limited only to standing on the ground, there are only two digits on each foot, and only a single one is to be found in thesolipedes(the horse, the ass).“Moreover, among these herbivorous animals, and especially among the ruminants, it has been found that from the circumstances of the desert countriesthey inhabit they are incessantly exposed to be the prey of carnivorous animals, and find safety only in precipitous flight. Necessity has forced them to run swiftly; and from the habit they have thus acquired their body has become slenderer and their limbs much more delicate: we see examples in the antelopes, the gazelles, etc.“Other dangers in our climate to which are continually exposed the deer, the roebuck, the fallow-deer, of perishing from the chase made by man, have reduced them to the same necessity, restrained them to similar habits, and have given rise to the same results.“The ruminating animals only using their legs as supports, and not having strong jaws, which are only exercised in cutting and browsing on grass, can only fight by striking with the head, by directing against each other thevertexof this part.“In their moments of anger, which are frequent, especially among the males, their internal feelings, by their efforts, more strongly urge the fluids toward this part of their head, and it there secretes the corneous matter in some, and osseous matter mixed with corneous matter in others, which gives origin to solid protuberances; hence the origin of horns and antlers, with which most of these animals have the head armed.“As regards habits, it is curious to observe the results in the special form and height of the giraffe (camelopardalis); we know that this animal, the tallest of mammals, inhabits the interior of Africa, and that it lives in localities where the earth, almost always arid and destitute of herbage, obliges it to browse on the foliage of trees, and to make continual efforts to reach it. It has resulted from this habit, maintained for a long period in all the individuals of its race, that its forelegs have become longer than the hinder ones, and that its neck is so elongated thatthe giraffe, without standing on its hind legs, raises its head and reaches six meters in height (almost twenty feet).“Among the birds, the ostriches, deprived of the power of flight, and raised on very long legs, probably owe their singular conformation to analogous circumstances.“The result of habits is as remarkable in the carnivorous mammals as it is in the herbivorous, but it presents effects of another kind.“Indeed, those of these mammals which are habituated, as their race, both to climb as well as to scratch or dig in the ground, or to tear open and kill other animals for food, have been obliged to use the digits of their feet; moreover, this habit has favored the separation of their digits, and has formed the claws with which they are armed.“But among the carnivores there are some which are obliged to run in order to overtake their prey; moreover, since these need and consequently have the habit of daily tearing with their claws and burying them deeply in the body of another animal, to seize and then to tear the flesh, and have been enabled by their repeated efforts to procure for these claws a size and curvature which would greatly interfere in walking or running on stony soil, it has resulted in this case that the animal has been obliged to make other efforts to draw back these too salient and curved claws which would impede it, and hence there has resulted the gradual formation of those special sheaths in which the cats, tigers, lions, etc., withdraw their claws when not in action.“Thus the efforts in any direction whatever, maintained for a long time or made habitually by certain parts of a living body to satisfy necessities called out by nature or by circumstances, develop these parts and make them acquire dimensions and a shape which they never would have attained if these effortshad not become the habitual action of the animals which have exercised them. The observations made on all the animals known will everywhere furnish examples.“Can any of them be more striking than that which thekangaroooffers us? This animal, which carries its young in its abdominal pouch, has adopted the habit of holding itself erect, standing only on its hind feet and tail, and only changing its position by a series of leaps, in which it preserves its erect attitude so as not to injure its young.“Let us see the result:“1. Its fore legs, of which it makes little use, and on which it rests only during the instant when it leaves its erect attitude, have never reached a development proportionate to that of the other parts, and have remained thin, very small, and weak;“2. The hind legs, almost continually in action, both for supporting the body and for leaping, have, on the contrary, obtained a considerable development, and have become very large and strong;“3. Finally, the tail, which we see is of much use in supporting the animal and in the performance of its principal movements, has acquired at its base a thickness and a strength extremely remarkable.“These well-known facts are assuredly well calculated to prove what results from the habitual use in the animals of any organ or part; and if, when there is observed in an animal an organ especially well developed, strong, and powerful, it is supposed that its habitual use has not produced it, that its continual disuse will make it lose nothing, and, finally, that this organ has always been such since the creation of the species to which this animal belongs, I will ask why our domestic ducks cannot fly like wild ducks—in a word, I might cite a multitude of examples which prove the differences in us resulting from the exercise or lack of use of such of our organs, although thesedifferences might not be maintained in the individuals which follow them genetically, for then their products would be still more considerable.“I shall prove, in the second part, that when the will urges an animal to any action, the organs which should execute this action are immediately provoked by the affluence of subtile fluids (the nervous fluid), which then become the determining cause which calls for the action in question. A multitude of observations prove this fact, which is now indisputable.“It results that the multiplied repetitions of these acts of organization strengthen, extend, develop, and even create the organs which are necessary. It is only necessary attentively to observe that which is everywhere occurring to convince ourselves of the well-grounded basis of this cause of organic developments and changes.“Moreover, every change acquired in an organ by a habit of use sufficient to have produced it is then preserved by heredity (génération) if it is common to the individuals which, in fecundation, unite in the reproduction of their species. Finally, this change is propagated, and thus is transmitted to all the individuals which succeed and which are submitted to the same circumstances, unless they have been obliged to acquire it by the means which have in reality created it.“Besides, in reproductive unions the crossings between the individuals which have different qualities or forms are necessarily opposed to the continuous propagation of these qualities and these forms. We see that in man, who is exposed to so many diverse circumstances which exert an influence on him, the qualities or the accidental defects which he has been in the way of acquiring, are thus prevented from being preserved and propagated by generation. If, when some particular features of form or any defects are acquired, two individuals under this condition shouldalways pair, they would reproduce the same features, and the successive generations being confined to such unions, a special and distinct race would then be formed. But perpetual unions between individuals which do not have the same peculiarities of form would cause all the characteristics acquired by special circumstances to disappear.“From this we can feel sure that if distances of habitation did not separate men the intermixture by generation would cause the general characteristics which distinguish the different nations to disappear.“If I should choose to pass in review all the classes, all the orders, all the genera, and all the species of animals which exist, I should show that the structure of individuals and their parts, their organs, their faculties, etc., etc., are in all cases the sole result of the circumstances in which each species is found to be subjected by nature and by the habits which the individuals which compose it have been obliged to contract, and which are only the product of a power primitively existing, which has forced the animals into their well-known habits.“We know that the animal called theai, or the sloth (Bradypus tridactylus), is throughout life in a condition so very feeble that it is very slow and limited in its movements, and that it walks on the ground with much difficulty. Its movements are so slow that it is thought that it cannot walk more than fifty steps in a day. It is also known that the structure of this animal is in direct relation with its feeble state or its inaptitude for walking; and that should it desire to make any other movements than those which it is seen to make, it could not do it.“Therefore, supposing that this animal had received from nature its well-known organization, it is said that this organization has forced it to adopt the habits and the miserable condition it is in.“I am far from thinking so; because I amconvinced that the habits which the individuals of the race of theaiwere originally compelled to contract have necessarily brought their organization into its actual state.“Since continual exposure to dangers has at some time compelled the individuals of this species to take refuge in trees and to live in them permanently, and then feed on their leaves, it is evident that then they would give up making a multitude of movements that animals which live on the ground perform.“All the needs of theaiwould then be reduced to seizing hold of the branches, to creeping along them or to drawing them in so as to reach the leaves, and then to remain on the tree in a kind of inaction, so as to prevent falling. Besides, this kind of sluggishness would be steadily provoked by the heat of the climate; for in warm-blooded animals the heat urges them rather to repose than to activity.“Moreover, during a long period of time the individuals of the race of theaihaving preserved the habit of clinging to trees and of making only slow and slightly varied movements, just sufficient for their needs, their organization has gradually become adapted to their new habits, and from this it will result:“1. That the arms of these animals making continual efforts readily to embrace the branches of trees, would become elongated;“2. That the nails of their digits would acquire much length and a hooked shape, by the continued efforts of the animal to retain its hold;“3. That their digits never having been trained to make special movements, would lose all mobility among themselves, would become united, and would only preserve the power of bending or of straightening out all together;“4. That their thighs, continually embracing both the trunks and the larger branches of trees, would contract a condition of habitual separation whichwould tend to widen the pelvis and to cause the cotyloid cavities to be directed backward;“5. Finally, that a great number of their bones would become fused, and hence several parts of their skeleton would assume an arrangement and a figure conformed to the habits of these animals, and contrary to what would be necessary for them to have for other habits.“Indeed, this can never be denied, because, in fact, nature on a thousand other occasions shows us, in the power exercised by circumstances on habits, and in that of the influence of habits on forms, dispositions, and the proportion of the parts of animals, truly analogous facts.“A great number of citations being unnecessary, we now see to what the case under discussion is reduced.“The fact is that divers animals have each, according to their genus and their species, special habits, and in all cases an organization which is perfectly adapted to these habits.“From the consideration of this fact, it appears that we should be free to admit either one or the other of the following conclusions, and that only one of them is susceptible of proof.“Conclusion admitted up to this day: Nature (or its Author), in creating the animals, has foreseen all the possible kinds of circumstances in which they should live, and has given to each species an unchanging organization, as also a form determinate and invariable in its different parts, which compels each species to live in the places and in the climate where we find it, and has there preserved its known habits.“My own conclusion: Nature, in producing in succession every species of animal, and beginning with the least perfect or the simplest to end her work with the most perfect, has gradually complicated their structure; and these animals spreading generally throughoutall the inhabitable regions of the globe, each species has received, through the influence of circumstances to which it has been exposed, the habits which we have observed, and the modifications in its organs which observation has shown us it possesses.“The first of these two conclusions is that believed up to the present day—namely, that held by nearly every one; it implies, in each animal, an unchanging organization and parts which have never varied, and which will never vary; it implies also that the circumstances of the places which each species of animal inhabits will never vary in these localities; for should they vary, the same animals could not live there, and the possibility of discovering similar forms elsewhere, and of transporting them there, would be forbidden.“The second conclusion is my own: it implies that, owing to the influence of circumstances on habits, and as the result of that of habits on the condition of the parts and even on that of the organization, each animal may receive in its parts and its organization, modifications susceptible of becoming very considerable, and of giving rise to the condition in which we find all animals.“To maintain that this second conclusion is unfounded, it is necessary at first to prove that each point of the surface of the globe never varies in its nature, its aspect, its situation whether elevated or depressed, its climate, etc., etc.; and likewise to prove that any part of animals does not undergo, even at the end of a long period, any modification by changes of circumstances, and by the necessity which directs them to another kind of life and action than that which is habitual to them.“Moreover, if a single fact shows that an animal for a long time under domestication differs from the wild form from which it has descended, and if in such a species in domesticity we find a great difference in conformation between the individuals submitted tosuch habits and those restricted to different habits, then it will be certain that the first conclusion does not conform to the laws of nature, and that, on the contrary, the second is perfectly in accord with them.“Everything combines then to prove my assertion—namely, that it is not the form, either of the body or of its parts, which gives rise to habits, and to the mode of life among animals; but that it is on the contrary the habits, the manner of living, and all the other influencing circumstances which have, after a time, constituted the form of the body and of the parts of animals. With the new forms, new faculties have been acquired, and gradually nature has come to form the animals as we actually see them.“Can there be in natural history a consideration more important, and to which we should give more attention, than that which I have just stated?“We will end this first part with the principles and the exposition of the natural classification of animals.”
“We do not here have to do with a line of argument, but with the examination of a positive fact, which is more general than is supposed, and whichhas not received the attention it deserves, doubtless because, very often, it is quite difficult to discover. This fact consists in the influence which circumstances exert on the different organisms subjected to them.
“In truth, for a long time there has been noticed the influence of different states of our organization on our character, our propensities (penchants), our actions, and even our ideas; but it seems to me that no one has yet recognized that of our actions and of our habits on our organization itself. Now, as these actions and these habits entirely depend on the circumstances in which we habitually find ourselves, I shall try to show how great is the influence which these circumstances exercise on the general form, on the condition of the parts, and even on the organization of living bodies. It is therefore this very positive fact which is to be the subject of this chapter.
“If we have not had numerous occasions to plainly recognize the effects of this influence on certain organisms which we have transported under entirely new and different circumstances, and if we had not seen these effects and the changes resulting from them produced, in a way, under our very eyes, the important fact in question would have always remained unknown.
“The influence of circumstances is really continuously and everywhere active on living beings, but what renders it difficult for us to appreciate this influence is that its effects only become sensible or recognizable (especially in the animals) at the end of a long period.
“Before stating and examining the proofs of this fact, which deserves our attention, and which is very important for a zoölogical philosophy, let us resume the thread of the considerations we had begun to discuss.
“In the preceding paragraph we have seen that it is now an incontrovertible fact that, in consideringthe animal scale in a sense the inverse of that of nature, we find that there exists in the groups composing this scale a continuous but irregular modification (dégradation) in the organization of animals which they comprise, an increasing simplification in the organization of these organisms; finally, a proportionate diminution in the number of faculties of these beings.
“This fact once recognized may throw the greatest light on the very order which nature has followed in the production of all the existing animals; but it does not show why the structure of animals in its increasing complexity from the more imperfect up to the most perfect offers only an irregular gradation, whose extent presents a number of anomalies or digressions which have no appearance of order in their diversity.
“Now, in seeking for the reason of this singular irregularity in the increasing complexity of organization of animals, if we should consider the outcome of the influences that the infinitely diversified circumstances in all parts of the globe exercise on the general form, the parts, and the very organization of these animals, everything will be clearly explained.
“It will, indeed, be evident that the condition in which we find all animals is, on one side, the result of the increasing complexity of the organization which tends to form a regular gradation, and, on the other, that it is that of the influences of a multitude of very different circumstances which continually tend to destroy the regularity in the gradations of the increasing complexity of the organization.
“Here it becomes necessary for me to explain the meaning I attach to the expressioncircumstances influencing the form and structure of animals—namely, that in becoming very different they change, with time, both their form and organization by proportionate modifications.
“Assuredly, if these expressions should be taken literally, I should be accused of an error; for whatever may be the circumstances, they do not directly cause any modification in the form and structure of animals.
“But the great changes in the circumstances bring about in animals great changes in their needs, and such changes in their needs necessarily cause changes in their actions. Now, if the new needs become constant or very permanent, the animals then assume newhabits, which are as durable as the needs which gave origin to them. We see that this is easily demonstrated and even does not need any explanation to make it clearer.
“It is then evident that a great change in circumstances having become constant in a race of animals leads these animals into new habits.
“Now, if new circumstances, having become permanent in a race of animals, have given to these animals newhabits—that is to say, have led them to perform new actions which have become habitual—there will from this result the use of such a part by preference to that of another, and in certain cases the total lack of use of any part which has become useless.
“Nothing of all this should be considered as a hypothesis or as a mere peculiar opinion; they are, on the contrary, truths which require, in order to be made evident, only attention to and the observation of facts.
“We shall see presently by the citation of known facts which prove it, on one side that the new wants, having rendered such a part necessary, have really by the result of efforts given origin to this part, and that as the result of its sustained use it has gradually strengthened it, developed, and has ended in considerably increasing its size; on the other side we shall see that, in certain cases, the new circumstancesand new wants having rendered such a part wholly useless, the total lack of use of this part has led to the result that it has gradually ceased to receive the development which the other parts of the animal obtain; that it gradually becomes emaciated and thin; and that finally, when this lack of use has been total during a long time, the part in question ends in disappearing. All this is a positive fact; I propose to give the most convincing proofs.
“In the plants, where there are no movements, and, consequently, no habits properly so called, great changes in circumstances do not bring about less great differences in the development of their parts; so that these differences originate and develop certain of them, while they reduce and cause several others to disappear. But here everything operates by the changes occurring in the nutrition of the plant, in its absorptions and transpirations, in the amount of heat, light, air, and humidity which it habitually receives; finally, in the superiority that certain of the different vital movements may assume over others.
“Between individuals of the same species, some of which are constantly well nourished, and in circumstances favorable to their entire development, while the others live under reversed circumstances, there is brought about a difference in the condition of these individuals which gradually becomes very remarkable. How many examples could I not cite regarding animals and plants, which would confirm the grounds for this view! Now, if the circumstances remain the same, rendering habitual and constant the condition of individuals badly fed, diseased, or languishing, their internal organization becomes finally modified, and reproduction between the individuals in question preserves the acquired modifications, and ends in giving rise to a race very distinct from that of the individuals which unceasingly meet with circumstances favorable to their development.
“A very dry spring-time is the cause of the grass of a field growing very slowly, remaining scraggy and puny, flowering and fruiting without growing much.
“A spring interspersed with warm days and rainy days makes the same grass grow rapidly, and the harvest of hay is then excellent.
“But if any cause perpetuates the unfavorable circumstances surrounding these plants, they vary proportionally, at first in their appearance and general condition, and finally in several particulars of their characters.
“For example, if some seed of any of the grasses referred to should be carried into an elevated place, on a dry and stony greensward much exposed to the winds, and should germinate there, the plant which should be able to live in this place would always be badly nourished, and the individuals reproduced there continuing to exist under these depressing circumstances, there would result a race truly different from that living in the field, though originating from it. The individuals of this new race would be small, scraggy, and some of their organs, having developed more than others, would then offer special proportions.
“Those who have observed much, and who have consulted the great collections, have become convinced that in proportion as the circumstances of habitat, exposure, climate, food, mode of life, etc., come to change, the characters of size, form, proportion between the parts, color, consistence, agility, and industry in the animals change proportionally.
“What nature accomplishes after a long time, we bring about every day by suddenly changing, in the case of a living plant, the circumstances under which it and all the individuals of its species exist.
“All botanists know that the plants which they transplant from their birthplace into gardens for cultivation gradually undergo changes which at last render them unrecognizable. Many plants naturallyvery hairy then become glabrous, or almost so; many of those which were creeping and trailing, then become erect; others lose their spines or their prickles; others still, from the woody and perennial condition which their stem possesses in a warm climate, pass, in our climate, into an herbaceous condition, and among these several are nothing more than annual plants; finally, the dimensions of their parts themselves undergo very considerable changes. These effects of changes of circumstances are so well known that botanists prefer not to describe garden plants, at least only those which have been newly cultivated.
“Is not cultivated wheat (Triticum sativum) only a plant brought by man into the condition in which we actually see it? Who can tell me in what country such a plant lives in a state of nature—that is to say, without being there the result of its culture in some neighboring region?
“Where occur in nature our cabbage, lettuce, etc., in the condition in which we see them in our kitchen-gardens? Is it not the same as regards a number of animals which domestication has changed or considerably modified?
“What very different races among our fowls and domestic pigeons, which we have obtained by raising them in different circumstances and in different countries, and how vainly do we now endeavor to rediscover them in nature!
“Those which are the least changed, without doubt by a more recent process of domestication, and because they do not live in a climate which is foreign to them, do not the less possess, in the condition of some of their parts, great differences produced by the habits which we have made them contract. Thus our ducks and our domestic geese trace back their type to the wild ducks and geese; but ours have lost the power of rising into the high regions of the air, and of flying over extensive regions; finally, a decidedchange has been wrought in the state of their parts compared with that of animals of the race from which they have descended.
“Who does not know that such a native bird, which we raise in a cage and which lives there five or six years in succession, and after that replaced in nature—namely, set free—is then unable to fly like its fellows which have always been free? The slight change of circumstance operating on this individual has only diminished its power of flight, and doubtless has not produced any change in the shape of its parts. But if a numerous series of generations of individuals of the same race should have been kept in captivity for a considerable time, there is no doubt but that even the form of the parts of these individuals would gradually undergo notable changes. For a much stronger reason, if, instead of a simple captivity constantly maintained over them, this circumstance had been at the same time accompanied by a change to a very different climate, and if these individuals by degrees had been habituated to other kinds of food, and to other kinds of movements to obtain it; certainly these circumstances, united and becoming constant, would insensibly form a new and special race.
“Where do we find, in nature, this multitude of races ofdogs, which, as the result of domesticity to which we have reduced these animals, have been brought into their present condition? Where do we find these bull-dogs, greyhounds, water spaniels, spaniels, pug-dogs, etc., etc., races which present among themselves much greater differences than those which we admit to be specific in wild animals of the same genus?
“Without doubt, a primitive single race, very near the wolf, if it is not itself the true type, has been submitted by man, at some period, to the process of domestication. This race, which then offered no difference between its individuals, has been graduallydispersed by man into different countries, with different climates; and after a time these same individuals, having undergone the influences of their habitats, and of the different habits they were obliged to contract in each country, have undergone remarkable changes, and have formed different special races. Now, the man who, for commercial reasons or from interests of any other kind, travels a very great distance, having carried into a densely populated place, as for example a great capital, different races of dogs originated in some very distant country, then the increase of these races by heredity (génération) has given rise successively to all those we now know.
“The following fact proves, as regards plants, how a change in any important circumstance leads to a change in the parts of their organisms.
“So long asRanunculus aquatilisis submerged in the water, its leaves are all finely incised and the divisions hair-like; but when the stalks of this plant reach the surface of the water, the leaves which grow out in the air are wider, rounded, and simply lobed. If some feet from the same plant the roots succeed in pushing into a soil only damp, without being submerged, their stalks then are short, none of their leaves are divided into capillary divisions, which gives rise toRanunculus hederaceus, which the botanists regard as a species whenever they meet with it.
“There is no doubt that as regards animals important changes in the circumstances under which they are accustomed to live do not produce alteration in their organs; for here the changes are much slower in operating than in plants, and, consequently, are to us less marked, and their cause less recognizable.
“As to the circumstances which have so much power in modifying the organs of living beings, the most influential are, doubtless, the diversity of the surroundings in which they live; but besides thisthere are many others which, in addition, have a considerable influence in the production of the effects in question.
“It is known that different localities change in nature and quality owing to their position, their nature, and their climate, as is easily seen in passing over different places distinguished by special features; hence we see a cause of variation for the animals and plants which live in these different places. But what we do not sufficiently know, and even what we generally refuse to believe, is that each place itself changes with time in exposure, in climate, in nature, and quality, although with a slowness so great in relation to our own continuance that we attribute to it a perfect stability.
“Now, in either case, these changed localities proportionally change the circumstances relative to the organisms which inhabit them, and the latter then give rise to other influences bearing on these same beings.
“We perceive from this that, if there are extremes in these changes, there are also gradations—namely, degrees which are intermediate and which fill the interval. Consequently there are also gradations in the differences which distinguish what we callspecies.
“It is then evident that the whole surface of the earth offers, in the nature and situation of the matters which occupy its different points, a diversity of circumstances which is throughout in relation with that of the forms and parts of animals, independent of the special diversity which necessarily results from the progress of the composition of organization in each animal.
“In each locality where animals can live, the circumstances which establish there an order of things remain for a long time the same, and really change there only with a slowness so great that man cannot directly notice them. He is obliged to consultmonuments to recognize that in each one of these places the order of things that he discovers there has not always been the same, and to perceive that it will change more.
“The races of animals which live in each of these places should, then, retain their customary habits there also for a long time; hence to us seems an apparent constancy of races which we callspecies—constancy which has originated among us the idea that these races are as ancient as nature.
“But in the different points of the earth’s surface which can be inhabited, nature and the situation of the places and climates constitute there, for the animals as for the plants,different circumstancesof all sorts of degrees. The animals which inhabit these different places should then differ from each other, not only on account of the state of nature of the organization in each race, but, besides, by reason of the habits that the individuals of each race there are forced to have; so, in proportion as he traverses the larger parts of the earth’s surface the observing naturalist sees circumstances changing in a manner somewhat noticeable; he constantly sees that the species change proportionately in their characters.
“Now, the true order of things necessary to consider in all this consists in recognizing:
“1. That every slight change maintained under the circumstances where occur each race of animals, brings about in them a real change in their wants.
“2. That every change in the wants of animals necessitates in them other movements (actions) to satisfy the new needs, and consequently other habits.
“3. That every new want necessitating new actions to satisfy it, demands of the animal which feels it both the more frequent use of such of its parts of which before it made less use, which develops and considerably enlarges them, and the use of new parts which necessity has caused to insensibly develop in it bythe effects of its inner feelings; which I shall constantly prove by known facts.
“Thus, to arrive at a knowledge of the true causes of so many different forms and so many different habits of which the known animals offer us examples, it is necessary to consider that circumstances infinitely diversified, but all slowly changing, into which the animals of each race are successively thrown, have caused, for each of them, new wants and necessarily changes in their habits. Moreover, this truth, which cannot be denied, being once recognized, it will be easy to see how the new needs have been able to be satisfied, and the new habits formed, if any attention be given to the two following laws of nature, which observation always confirms:
“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, causes it to become reduced, progressively diminishes its faculties, and ends in its disappearance.
“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 (génération) and passes on to the new individuals which descend from it, provided that the changes thus acquired are common to both sexes, orto 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, or only by those who allow themselves to fall into the error which I have combated.
“Naturalists having observed that the forms of the parts of animals compared with the uses of these parts are always in perfect accord, have thought that the forms and conditions of parts have caused the function; but this is a mistake, for it is easy to demonstrate by observation that it is, on the contrary, the needs and uses of organs which have developed these same parts, which have even given origin to them where they did not exist, and which consequently have given rise to the condition in which we observe them in each animal.
“If this were not so, it would have been necessary for nature to have created for the parts of animals as many forms as the diversity of circumstances in which they have to live had required, and that these forms and also the circumstances had never varied.
“This is certainly not the existing order of things, and if it were really such, we should not have the race-horses of England; we should not have our great draft horses, so clumsy and so different from the first named, for nature herself has not produced their like; we should not, for the same reason, have terrier dogs with bow legs, greyhounds so swift in running, water-spaniels, etc.; we should not have tailless fowls, fantail pigeons, etc.; finally, we could cultivate the wild plants as much as we pleased in the rich and fertile soil of our gardens without fearing to see them change by long culture.
“For a long time we have felt the force of the saying which has passed into the well-known proverb—habits form a second nature.
“Assuredly, if the habits and nature of each animal can never vary, the proverb is false, has no foundation, and does not apply to the instances which led to its being spoken.
“If we should seriously consider all that I have just stated, it might be thought that I had good reason when in my work entitledRecherches sur les Corps vivans(p. 50) I established the following proposition:
“‘It is not the organs—that is to say, the nature and form of the parts of the body of an animal—which have given rise to its habits and its special faculties; but it is, on the contrary, its habits, its manner of life, and the circumstances in which are placed the individuals from which it originates, which have, with time, brought about the form of its body, the number and condition of its organs, finally, the faculties which it enjoys.’
“If we weigh this proposition, and if we recall all the observations which nature and the state of things continually lead us to do, then its importance and its solidity will become more evident.
“Time and favorable circumstances are, as I have already said, the two principal means which nature employs to give existence to all her productions: we know that time for her has no limits, and that consequently it is ever at her disposal.
“As to the circumstances of which she has need, and which she uses still daily to cause variations in all that she continues to produce, we can say that they are, in some degree, for her inexhaustible.
“The principal circumstances arise from the influence of climate; from those of different temperatures of the atmosphere, and from all the environing media; from that of the diversity of different localities and their situation; from that of habits, the ordinary movements, the most frequent actions; finally, from that of means of preservation, of mode of living, of defence, of reproduction, etc.
“Moreover, owing to these diverse influences, the faculties increase and become stronger by use, become differentiated by the new habits preserved for long ages, and insensibly the organization, the consistence—in a word, the nature and condition of parts, as also of the organs—participate in the results of all these influences, become preserved, and are propagated by generation.
“These truths, which are only the results of the two natural laws above stated, are in every case completely confirmed by facts; they clearly indicate the course of nature in all the diversity of its products.
“But instead of contenting ourselves with generalities which might be considered as hypothetical, let us directly examine the facts, and consider, in the animals, the result of the use or disuse of their organs on the organs themselves, according to the habits that each race has been compelled to contract.
“I shall now attempt to prove that the constant lack of exercise of organs at first diminishes their faculties, gradually impoverishes them, and ends by making them disappear, or even causing them to be atrophied, if this lack of use is perpetuated for a very long time through successive generations of animals of the same race.
“I shall next prove that, on the contrary, the habit of exercising an organ, in every animal which has not attained the limit of the diminution of its faculties, not only perfects and increases the faculties of this organ, but, besides, enables it to acquire developments and dimensions which insensibly change it; so that with time it renders it very different from the same organ in another animal which exercises it much less.
“The lack of use of an organ, become constant by the habits formed, gradually impoverishes this organ, and ends by causing it to disappear and even to destroy it.
“As such a proposition can only be admitted on proof, and not by its simple announcement, let usprove it by the citation of the leading known facts on which it is based.
“The vertebrate animals, whose plan of organization is in all nearly the same, although they offer much diversity in their parts, have jaws armed withteeth; moreover, those among them which circumstances have placed in the habit of swallowing their food without previousmasticationare exposed to the result that their teeth become undeveloped. These teeth, then, either remain concealed between the bony edges of the jaws, without appearing above, or even their gums are found to have been atrophied.
“In the baleen whales, which have been supposed to be completely deprived of teeth, M. Geoffroy has found them concealed in the jaws of thefœtusof this animal. This professor has also found in the birds the groove where the teeth should be situated; but they are no longer to be seen there.
“In the class even of mammals, which comprises the most perfect animals, and chiefly those in which the vertebrate plan of organization is most perfectly carried out, not only the baleen has no usable teeth, but the ant-eater (Myrmecophaga) is also in the same condition, whose habit of not masticating its food has been for a long time established and preserved in its race.
“The presence of eyes in the head is a characteristic of a great number of different animals, and becomes an essential part of the plan of organization of vertebrates.
“Nevertheless the mole, which owing to its habits makes very little use of vision, has only very small eyes, which are scarcely visible, since they exercise these organs to a very slight extent.
“TheAspalaxof Olivier (Voyage en Egypte et en Perse, ii. pl. 28 f. 2), which lives under ground like the mole, and which probably exposes itself still less than that animal to the light of day, has totally lost thepower of sight; also it possesses only vestiges of the organ of which it is the seat; and yet these vestiges are wholly concealed under the skin and other parts which cover them, and do not permit the least access to the light.
“TheProteus, an aquatic reptile allied to the salamander in its structure, and which lives in the dark subterranean waters of deep caves, has, like theAspalax, only vestiges of the organs of sight—vestiges which are covered and concealed in the same manner.
“We turn to a decisive consideration relative to this question.
“Light does not penetrate everywhere; consequently animals which habitually live in situations where it does not penetrate lack the occasion of exercising the organs of sight, if nature has provided them with them. Moreover, the animals which make part of the plan of organization in whicheyesare necessarily present, have originally had them. However, since we find them among those which are deprived of the use of this organ, and which have only vestiges concealed and covered over, it should be evident that the impoverishment and even the disappearance of these organs are the result of a constant lack of exercise.
“What proves it is that the organ ofhearingis never in this condition, and that we always find it in the animals when the nature of their organization should require its existence; the reason is as follows.
“Thecause of sound, that which, moved by the shock or the vibrations of bodies, transmits to the organ of hearing the impression which it receives, penetrates everywhere, traverses all the media, and even the mass of the densest bodies: from this it results that every animal which makes a part of a plan of organization to whichhearingis essential, has always occasion to exercise this organ in whatever situation it lives. So, among thevertebrate animalswe see none deprived of their organs of hearing; but in the groups below them, when the same organs are once wanting, we do not again find them.
“It is not so with the organ of sight, for we see this organ disappear, reappear, and again disappear, in proportion to the possibility or impossibility of the animal’s exercising it.
“In theacephalous molluscs, the great development of the mantle of these molluscs has rendered their eyes and even their head entirely useless. These organs, also forming a part of a plan of organization which should comprise them, have disappeared and atrophied from constant lack of use.
“Finally, it is a part of the plan of organization ofreptiles, as in other vertebrate animals, to have four legs appended to their skeleton. The serpents should consequently have four, though they do not form the lowest order of reptiles, and are not so near the fishes as the batrachians (the frogs, the salamanders, etc.).
“However, the serpents having taken up the habit of gliding along the ground, and of concealing themselves in the grass, their body, owing to continually repeated efforts to elongate itself so as to pass through narrow spaces, has acquired a considerable length disproportionate to its size. Moreover, limbs would have been very useless to these animals, and consequently would not have been employed: because long legs would have interfered with their need of gliding, and very short legs, not being more than four in number, would have been incapable of moving their body. Hence the lack of use of these parts having been constant in the races of these animals, has caused the total disappearance of these same parts, although really included in the plan of organization of the animals of their class.
“Many insects which by the natural character of their order, and even of their genus, should have wings, lack them more or less completely fromdisuse. A quantity of Coleoptera, Orthoptera, Hymenoptera, and of Hemiptera, etc., afford examples; the habits of these animals do not require them to make use of their wings.
“But it is not sufficient to give the explanation of the cause which has brought about the condition of the organs of different animals—a condition which we see to be always the same in those of the same species; we must besides observe the changes of condition produced in the organs of one and the same individual during its life, by the single result of a great change in the special habits in the individuals of its species. The following fact, which is one of the most remarkable, will serve to prove the influence of habits on the condition of organs, and show how changes wrought in the habits of an individual, produce the condition of the organs which are brought into action during the exercise of these habits.
“M. Tenon, member of the Institute, has given an account to the Class of Sciences, that having examined the intestinal canal of several men who had been hard drinkers all their lives, he had constantly found it to be shortened to an extraordinary extent, compared with the same organ in those not given to such a habit.
“We know that hard drinkers, or those who are addicted to drunkenness, take very little solid food, that they eat very lightly, and that the beverage which they take in excess frequently suffices to nourish them.
“Moreover, as fluid aliments, especially spirituous liquors, do not remain a long time either in the stomach or in the intestines, the stomach and the remainder of the intestinal canal lose the habit of being distended in intemperate persons, so also in sedentary persons and those engaged in mental labor, who are habituated to take but little food. Gradually and at length their stomach becomes contracted, and their intestines shortened.
“We are not concerned here with the shrinkage and shortening produced by a puckering of the parts, which permit ordinary extension, if instead of a continued emptiness these viscera should be filled; the shrinkage and shortening in question are real, considerable, and such that these organs would burst open rather than yield suddenly to the causes which would require ordinary extension.
“In circumstances of persons of the same age, compare a man who, in order to devote himself to habitual study and mental work, which have rendered his digestion more difficult, has contracted the habit of eating lightly, with another who habitually takes a good deal of exercise, walks out often, and eats heartily; the stomach of the first will be weakened, and a small quantity of food will fill it, while that of the second will be not only maintained in its ordinary health but even strengthened.
“We have here the case of an organ much modified in its dimensions and in its faculties by the single cause of a change in habits during the life of the individual.
“The frequent use of an organ become constant by habit increases the faculties of this organ, even develops it, and enables it to acquire dimensions and a power of action which it does not possess in animals which exercise less.
“We have just said that the lack of employment of an organ which necessarily exists modifies it, impoverishes it, and ends by its disappearing entirely.
“I shall now demonstrate that the continued employment of an organ, with the efforts made to draw out its powers under circumstances where it would be of service, strengthens, extends, and enlarges this organ, or creates a new one which can exercise the necessary functions.
“The bird which necessity drives to the water to find there prey fitted for its sustenance, opens the digits ofits feet when it wishes to strike the water and propel itself along its surface. The skin which unites these digits at their base, by these acts of spreading apart being unceasingly repeated contracts the habit of extending; so that after a while the broad membranes which connect the digits of ducks, geese, etc., are formed as we see them. The same efforts made in swimming—i.e., in pushing back the water, in order to advance and to move in this liquid—have likewise extended the membrane situated between the digits of the frogs, the sea-turtles, the otter, beaver, etc.
“On the contrary, the bird whose mode of life habituates it to perch on trees, and which is born of individuals who have all contracted this habit, has necessarily the digits of the feet longer and shaped in another way than those of the aquatic animals which I have just mentioned. Its claws, after a while, became elongated, pointed, and curved or hook-like in order to grasp the branches on which the animal often rests.
“Likewise we see that the shore bird, which is not inclined to swim, and which moreover has need of approaching the edge of the water to find there its prey, is in continual danger of sinking in the mud. Now, this bird, wishing to act so that its body shall not fall into the water, makes every effort to extend and elongate its legs. It results from this that the long-continued habit that this bird and the others of its race contract, of extending and continually elongating their legs, is thecauseof the individuals of this race being raised as if on stilts, having gradually acquired long, naked legs, which are denuded of feathers up to the thighs and often above them (Système des Animaux sans Vertèbres, p. 16).
“We also perceive that the same bird, wishing to catch fish without wetting its body, is obliged to make continual efforts to lengthen its neck. Now, the results of these habitual efforts in this individualand in those of its race have enabled them, after a time, to singularly elongate them—as, indeed, is proved by the long neck of all shore birds.
“If any swimming birds, such as the swan and the goose, whose legs are short, nevertheless have a very long neck, it is because these birds in swimming on the surface of the water have the habit of plunging their head down as far as they can, to catch aquatic larvæ and different animalcules for food, and because they make no effort to lengthen their legs.
“When an animal to satisfy its wants makes repeated efforts to elongate its tongue, it will acquire a considerable length (the ant-eater, green wood-pecker); when it is obliged to seize anything with this same organ, then its tongue will divide and become forked. That of the humming-birds, which seize with their tongue, and that of the lizard and serpents, which use it to feel and examine objects in front of them, are proofs of what I advocate.
“Wants, always occasioned by circumstances, and followed by sustained efforts to satisfy them, are not limited in results, in modifying—that is to say, in increasing or diminishing—the extent and the faculties of organs; but they also come to displace these same organs when certain of these wants become a necessity.
“The fishes which habitually swim in large bodies of water, having need of seeing laterally, have, in fact, their eyes placed on the sides of the head. Their bodies, more or less flattened according to thespecies, have their sides perpendicular to the plane of the water, and their eyes are placed in such a way that there is an eye on each flattened side. But those fishes whose habits place them under the necessity of constantly approaching the shores, and especially the shelving banks or where the slope is slight, have been forced to swim on their flattened faces, so as to be ableto approach nearer the edge of the water. In this situation, receiving more light from above than from beneath, and having a special need of being always attentive to what is going on above them, this need has forced one of their eyes to undergo a kind of displacement, and to assume the very singular situation which is familiar to us in thesoles,turbots,dabs, etc. (PleuronectesandAchirus). The situation of these eyes is asymmetrical, because this results from an incomplete change. Now, this change is entirely completed in the rays, where the transverse flattening of the body is entirely horizontal, as also the head. Also the eyes of the rays, both situated on the upper side, have become symmetrical.
“The serpents which glide along the surface of the ground are obliged chiefly to see elevated objects, or what are above their eyes. This necessity has brought an influence to bear on the situation of the organs of vision in these animals; and, in fact, they have the eyes placed in the lateral and upper parts of the head, so as to easily perceive what is above or at their sides; but they only see for a short distance what is in front of them. Moreover, forced to supply the lack of ability to see and recognize what is in front of their head, and which might injure them, they need only to feel such objects with the aid of their tongue, which they are obliged to dart out with all their power. This habit has not only contributed to render the tongue slender, very long and retractile, but has also led in a great number of species to its division, so as to enable them to feel several objects at once; it has likewise allowed them to form an opening at the end of their head, to enable the tongue to dart out without their being obliged to open their jaws.
“Nothing is more remarkable than the result of habits in the herbivorous mammals.
“The quadruped to whom circumstances and thewants which they have created have given for a long period, as also to others of its race, the habit of browsing on grass, only walks on the ground, and is obliged to rest there on its four feet the greater part of its life, moving about very little, or only to a moderate extent. The considerable time which this sort of creature is obliged to spend each day to fill itself with the only kind of food which it requires, leads it to move about very little, so that it uses its legs only to stand on the ground, to walk, or run, and they never serve to seize hold of or to climb trees.
“From this habit of daily consuming great amounts of food which distend the organs which receive it, and of only moving about to a limited extent, it has resulted that the bodies of these animals are thick, clumsy, and massive, and have acquired a very great volume, as we see in elephants, rhinoceroses, oxen, buffaloes, horses, etc.
“The habit of standing upright on their four feet during the greater part of the day to browse has given origin to a thick hoof which envelops the extremity of the digits of their feet; and as their toes are not trained to make any movement, and because they have served no other use than as supports, as also the rest of the leg, the most of them are short, are reduced in size, and even have ended by totally disappearing. Thus in thepachyderms, some have five toes enveloped in horn, and consequently their foot is divided into five parts; others have only four, and still others only three. But in theruminants, which seem to be the most ancient of mammals, which are limited only to standing on the ground, there are only two digits on each foot, and only a single one is to be found in thesolipedes(the horse, the ass).
“Moreover, among these herbivorous animals, and especially among the ruminants, it has been found that from the circumstances of the desert countriesthey inhabit they are incessantly exposed to be the prey of carnivorous animals, and find safety only in precipitous flight. Necessity has forced them to run swiftly; and from the habit they have thus acquired their body has become slenderer and their limbs much more delicate: we see examples in the antelopes, the gazelles, etc.
“Other dangers in our climate to which are continually exposed the deer, the roebuck, the fallow-deer, of perishing from the chase made by man, have reduced them to the same necessity, restrained them to similar habits, and have given rise to the same results.
“The ruminating animals only using their legs as supports, and not having strong jaws, which are only exercised in cutting and browsing on grass, can only fight by striking with the head, by directing against each other thevertexof this part.
“In their moments of anger, which are frequent, especially among the males, their internal feelings, by their efforts, more strongly urge the fluids toward this part of their head, and it there secretes the corneous matter in some, and osseous matter mixed with corneous matter in others, which gives origin to solid protuberances; hence the origin of horns and antlers, with which most of these animals have the head armed.
“As regards habits, it is curious to observe the results in the special form and height of the giraffe (camelopardalis); we know that this animal, the tallest of mammals, inhabits the interior of Africa, and that it lives in localities where the earth, almost always arid and destitute of herbage, obliges it to browse on the foliage of trees, and to make continual efforts to reach it. It has resulted from this habit, maintained for a long period in all the individuals of its race, that its forelegs have become longer than the hinder ones, and that its neck is so elongated thatthe giraffe, without standing on its hind legs, raises its head and reaches six meters in height (almost twenty feet).
“Among the birds, the ostriches, deprived of the power of flight, and raised on very long legs, probably owe their singular conformation to analogous circumstances.
“The result of habits is as remarkable in the carnivorous mammals as it is in the herbivorous, but it presents effects of another kind.
“Indeed, those of these mammals which are habituated, as their race, both to climb as well as to scratch or dig in the ground, or to tear open and kill other animals for food, have been obliged to use the digits of their feet; moreover, this habit has favored the separation of their digits, and has formed the claws with which they are armed.
“But among the carnivores there are some which are obliged to run in order to overtake their prey; moreover, since these need and consequently have the habit of daily tearing with their claws and burying them deeply in the body of another animal, to seize and then to tear the flesh, and have been enabled by their repeated efforts to procure for these claws a size and curvature which would greatly interfere in walking or running on stony soil, it has resulted in this case that the animal has been obliged to make other efforts to draw back these too salient and curved claws which would impede it, and hence there has resulted the gradual formation of those special sheaths in which the cats, tigers, lions, etc., withdraw their claws when not in action.
“Thus the efforts in any direction whatever, maintained for a long time or made habitually by certain parts of a living body to satisfy necessities called out by nature or by circumstances, develop these parts and make them acquire dimensions and a shape which they never would have attained if these effortshad not become the habitual action of the animals which have exercised them. The observations made on all the animals known will everywhere furnish examples.
“Can any of them be more striking than that which thekangaroooffers us? This animal, which carries its young in its abdominal pouch, has adopted the habit of holding itself erect, standing only on its hind feet and tail, and only changing its position by a series of leaps, in which it preserves its erect attitude so as not to injure its young.
“Let us see the result:
“1. Its fore legs, of which it makes little use, and on which it rests only during the instant when it leaves its erect attitude, have never reached a development proportionate to that of the other parts, and have remained thin, very small, and weak;
“2. The hind legs, almost continually in action, both for supporting the body and for leaping, have, on the contrary, obtained a considerable development, and have become very large and strong;
“3. Finally, the tail, which we see is of much use in supporting the animal and in the performance of its principal movements, has acquired at its base a thickness and a strength extremely remarkable.
“These well-known facts are assuredly well calculated to prove what results from the habitual use in the animals of any organ or part; and if, when there is observed in an animal an organ especially well developed, strong, and powerful, it is supposed that its habitual use has not produced it, that its continual disuse will make it lose nothing, and, finally, that this organ has always been such since the creation of the species to which this animal belongs, I will ask why our domestic ducks cannot fly like wild ducks—in a word, I might cite a multitude of examples which prove the differences in us resulting from the exercise or lack of use of such of our organs, although thesedifferences might not be maintained in the individuals which follow them genetically, for then their products would be still more considerable.
“I shall prove, in the second part, that when the will urges an animal to any action, the organs which should execute this action are immediately provoked by the affluence of subtile fluids (the nervous fluid), which then become the determining cause which calls for the action in question. A multitude of observations prove this fact, which is now indisputable.
“It results that the multiplied repetitions of these acts of organization strengthen, extend, develop, and even create the organs which are necessary. It is only necessary attentively to observe that which is everywhere occurring to convince ourselves of the well-grounded basis of this cause of organic developments and changes.
“Moreover, every change acquired in an organ by a habit of use sufficient to have produced it is then preserved by heredity (génération) if it is common to the individuals which, in fecundation, unite in the reproduction of their species. Finally, this change is propagated, and thus is transmitted to all the individuals which succeed and which are submitted to the same circumstances, unless they have been obliged to acquire it by the means which have in reality created it.
“Besides, in reproductive unions the crossings between the individuals which have different qualities or forms are necessarily opposed to the continuous propagation of these qualities and these forms. We see that in man, who is exposed to so many diverse circumstances which exert an influence on him, the qualities or the accidental defects which he has been in the way of acquiring, are thus prevented from being preserved and propagated by generation. If, when some particular features of form or any defects are acquired, two individuals under this condition shouldalways pair, they would reproduce the same features, and the successive generations being confined to such unions, a special and distinct race would then be formed. But perpetual unions between individuals which do not have the same peculiarities of form would cause all the characteristics acquired by special circumstances to disappear.
“From this we can feel sure that if distances of habitation did not separate men the intermixture by generation would cause the general characteristics which distinguish the different nations to disappear.
“If I should choose to pass in review all the classes, all the orders, all the genera, and all the species of animals which exist, I should show that the structure of individuals and their parts, their organs, their faculties, etc., etc., are in all cases the sole result of the circumstances in which each species is found to be subjected by nature and by the habits which the individuals which compose it have been obliged to contract, and which are only the product of a power primitively existing, which has forced the animals into their well-known habits.
“We know that the animal called theai, or the sloth (Bradypus tridactylus), is throughout life in a condition so very feeble that it is very slow and limited in its movements, and that it walks on the ground with much difficulty. Its movements are so slow that it is thought that it cannot walk more than fifty steps in a day. It is also known that the structure of this animal is in direct relation with its feeble state or its inaptitude for walking; and that should it desire to make any other movements than those which it is seen to make, it could not do it.
“Therefore, supposing that this animal had received from nature its well-known organization, it is said that this organization has forced it to adopt the habits and the miserable condition it is in.
“I am far from thinking so; because I amconvinced that the habits which the individuals of the race of theaiwere originally compelled to contract have necessarily brought their organization into its actual state.
“Since continual exposure to dangers has at some time compelled the individuals of this species to take refuge in trees and to live in them permanently, and then feed on their leaves, it is evident that then they would give up making a multitude of movements that animals which live on the ground perform.
“All the needs of theaiwould then be reduced to seizing hold of the branches, to creeping along them or to drawing them in so as to reach the leaves, and then to remain on the tree in a kind of inaction, so as to prevent falling. Besides, this kind of sluggishness would be steadily provoked by the heat of the climate; for in warm-blooded animals the heat urges them rather to repose than to activity.
“Moreover, during a long period of time the individuals of the race of theaihaving preserved the habit of clinging to trees and of making only slow and slightly varied movements, just sufficient for their needs, their organization has gradually become adapted to their new habits, and from this it will result:
“1. That the arms of these animals making continual efforts readily to embrace the branches of trees, would become elongated;
“2. That the nails of their digits would acquire much length and a hooked shape, by the continued efforts of the animal to retain its hold;
“3. That their digits never having been trained to make special movements, would lose all mobility among themselves, would become united, and would only preserve the power of bending or of straightening out all together;
“4. That their thighs, continually embracing both the trunks and the larger branches of trees, would contract a condition of habitual separation whichwould tend to widen the pelvis and to cause the cotyloid cavities to be directed backward;
“5. Finally, that a great number of their bones would become fused, and hence several parts of their skeleton would assume an arrangement and a figure conformed to the habits of these animals, and contrary to what would be necessary for them to have for other habits.
“Indeed, this can never be denied, because, in fact, nature on a thousand other occasions shows us, in the power exercised by circumstances on habits, and in that of the influence of habits on forms, dispositions, and the proportion of the parts of animals, truly analogous facts.
“A great number of citations being unnecessary, we now see to what the case under discussion is reduced.
“The fact is that divers animals have each, according to their genus and their species, special habits, and in all cases an organization which is perfectly adapted to these habits.
“From the consideration of this fact, it appears that we should be free to admit either one or the other of the following conclusions, and that only one of them is susceptible of proof.
“Conclusion admitted up to this day: Nature (or its Author), in creating the animals, has foreseen all the possible kinds of circumstances in which they should live, and has given to each species an unchanging organization, as also a form determinate and invariable in its different parts, which compels each species to live in the places and in the climate where we find it, and has there preserved its known habits.
“My own conclusion: Nature, in producing in succession every species of animal, and beginning with the least perfect or the simplest to end her work with the most perfect, has gradually complicated their structure; and these animals spreading generally throughoutall the inhabitable regions of the globe, each species has received, through the influence of circumstances to which it has been exposed, the habits which we have observed, and the modifications in its organs which observation has shown us it possesses.
“The first of these two conclusions is that believed up to the present day—namely, that held by nearly every one; it implies, in each animal, an unchanging organization and parts which have never varied, and which will never vary; it implies also that the circumstances of the places which each species of animal inhabits will never vary in these localities; for should they vary, the same animals could not live there, and the possibility of discovering similar forms elsewhere, and of transporting them there, would be forbidden.
“The second conclusion is my own: it implies that, owing to the influence of circumstances on habits, and as the result of that of habits on the condition of the parts and even on that of the organization, each animal may receive in its parts and its organization, modifications susceptible of becoming very considerable, and of giving rise to the condition in which we find all animals.
“To maintain that this second conclusion is unfounded, it is necessary at first to prove that each point of the surface of the globe never varies in its nature, its aspect, its situation whether elevated or depressed, its climate, etc., etc.; and likewise to prove that any part of animals does not undergo, even at the end of a long period, any modification by changes of circumstances, and by the necessity which directs them to another kind of life and action than that which is habitual to them.
“Moreover, if a single fact shows that an animal for a long time under domestication differs from the wild form from which it has descended, and if in such a species in domesticity we find a great difference in conformation between the individuals submitted tosuch habits and those restricted to different habits, then it will be certain that the first conclusion does not conform to the laws of nature, and that, on the contrary, the second is perfectly in accord with them.
“Everything combines then to prove my assertion—namely, that it is not the form, either of the body or of its parts, which gives rise to habits, and to the mode of life among animals; but that it is on the contrary the habits, the manner of living, and all the other influencing circumstances which have, after a time, constituted the form of the body and of the parts of animals. With the new forms, new faculties have been acquired, and gradually nature has come to form the animals as we actually see them.
“Can there be in natural history a consideration more important, and to which we should give more attention, than that which I have just stated?
“We will end this first part with the principles and the exposition of the natural classification of animals.”
In the fourth chapter of the third part (vol. ii. pp. 276–301) Lamarck treats of the internal feelings of certain animals, which provoke wants (besoins). This is the subject which has elicited so much adverse criticism and ridicule, and has in many cases led to the wholesale rejection of all of Lamarck’s views. It is generally assumed or stated by Lamarck’s critics, who evidently did not read his book carefully, that while he claimed that the plants were evolved by the direct action of the physical factors, that in the case of all the animals the process was indirect. But this is not correct. He evidently, as we shall see, places the lowest animals, those without (or what he supposed to be without) a nervous system, in the same category as the plants. He distinctly states at the outset thatonly certain animals and man are endowed with this singular faculty, “which consists in being able to experienceinternal emotionswhich provoke the wants and different external or internal causes, and which give birth to the power which enables them to perform different actions.”
“The nervous fluid,” he says, “can, then, undergo movements in certain parts of its mass, as well as in every part at once; moreover, it is these latter movements which constitute thegeneral movements(ébranlements) of this fluid, and which we now proceed to consider.
“The general movements of the nervous fluid are of two kinds; namely,“1. Partial movements (ébranlements), which finally become general and end in a reaction. It is the movements of this sort which produce feeling. We have treated of them in the third chapter.“2. The movements which are general from the time they begin, and which form no reaction. It is these which constitute internal emotions, and it is of them alone of which we shall treat.“But previously, it is necessary to say a word regarding thefeeling of existence, because this feeling is the source from which the inner emotions originate.“On the Feeling of Existence.“The feeling of existence (sentiment d’existence), which I shall callinner feeling,[183]so as to separate from it the idea of a general condition (généralité) which it does not possess, since it is not common toall living beings and not even to all animals, is a very obscure feeling, with which are endowed those animals provided with a nervous system sufficiently developed to give them the faculty of feeling.“This sentiment, very obscure as it is, is nevertheless very powerful, for it is the source of inner emotions which test (éprouvent) the individuals possessing it, and, as the result, this singular force urges these individuals to themselves produce the movements and the actions which their wants require. Moreover this feeling, considered as a very activemotor, only acts thus by sending to the muscles which necessarily cause these movements and actions the nervous fluid which excites them....“Indeed, as the result of organic or vital movements which are produced in every animal, that which possesses a nervous system sufficiently developed has physical sensibility and continually receives in every inner and sensitive part impressions which continually affect it, and which it feels in general without being able to distinguish any single one.“The sentiment of existence [consciousness] is general, since almost every sensitive part of the body shares in it. ‘It constitutes thisme(moi) with which all animals, which are only sensitive, are penetrated, without perceiving it, but which those possessing a brain are able to notice, having the power of thought and of giving attention to it. Finally, it is in all the source of a power which is aroused by wants, which acts effectively only by emotion, and through which the movements and actions derive the force which produces them’....“Finally, the inner feeling only manifests its power, and causes movements, when there exists a system for muscular movement, which is always dependent on the nervous system, and cannot take place without it.”
“The general movements of the nervous fluid are of two kinds; namely,
“1. Partial movements (ébranlements), which finally become general and end in a reaction. It is the movements of this sort which produce feeling. We have treated of them in the third chapter.
“2. The movements which are general from the time they begin, and which form no reaction. It is these which constitute internal emotions, and it is of them alone of which we shall treat.
“But previously, it is necessary to say a word regarding thefeeling of existence, because this feeling is the source from which the inner emotions originate.
“The feeling of existence (sentiment d’existence), which I shall callinner feeling,[183]so as to separate from it the idea of a general condition (généralité) which it does not possess, since it is not common toall living beings and not even to all animals, is a very obscure feeling, with which are endowed those animals provided with a nervous system sufficiently developed to give them the faculty of feeling.
“This sentiment, very obscure as it is, is nevertheless very powerful, for it is the source of inner emotions which test (éprouvent) the individuals possessing it, and, as the result, this singular force urges these individuals to themselves produce the movements and the actions which their wants require. Moreover this feeling, considered as a very activemotor, only acts thus by sending to the muscles which necessarily cause these movements and actions the nervous fluid which excites them....
“Indeed, as the result of organic or vital movements which are produced in every animal, that which possesses a nervous system sufficiently developed has physical sensibility and continually receives in every inner and sensitive part impressions which continually affect it, and which it feels in general without being able to distinguish any single one.
“The sentiment of existence [consciousness] is general, since almost every sensitive part of the body shares in it. ‘It constitutes thisme(moi) with which all animals, which are only sensitive, are penetrated, without perceiving it, but which those possessing a brain are able to notice, having the power of thought and of giving attention to it. Finally, it is in all the source of a power which is aroused by wants, which acts effectively only by emotion, and through which the movements and actions derive the force which produces them’....
“Finally, the inner feeling only manifests its power, and causes movements, when there exists a system for muscular movement, which is always dependent on the nervous system, and cannot take place without it.”
The author then states that these emotions of the organic sense may operate in the animals and in man either without or with an act of their will.
“From what has been said, we cannot doubt but that the inner and general feeling which urges the animals possessing a nervous system fitted for feeling should be susceptible of being aroused by the causes which affect it; moreover, these causes are always the need both of satisfying hunger, of escaping dangers, of avoiding pain, of seeking pleasure, or that which is agreeable to the individual, etc.“The emotions of the inner feeling can only be recognized by man, who alone pays attention to them, but he only perceives those which are strong, which excite his whole being, such as a view from a precipice, a tragic scene, etc.”
“From what has been said, we cannot doubt but that the inner and general feeling which urges the animals possessing a nervous system fitted for feeling should be susceptible of being aroused by the causes which affect it; moreover, these causes are always the need both of satisfying hunger, of escaping dangers, of avoiding pain, of seeking pleasure, or that which is agreeable to the individual, etc.
“The emotions of the inner feeling can only be recognized by man, who alone pays attention to them, but he only perceives those which are strong, which excite his whole being, such as a view from a precipice, a tragic scene, etc.”
Lamarck then divides the emotions into physical and moral, the latter arising from our ideas, thoughts—in short, our intellectual acts—in the account of which we need not follow him.
In the succeeding chapter (V.) the author dilates on the force which causes actions in animals. “We know,” he says “that plants can satisfy their needs without moving, since they find their food in the environingmilieux. But it is not the same with animals, which are obliged to move about to procure their sustenance. Moreover, most of them have other wants to satisfy, which require other kinds of movements and acts.” This matter is discussed in the author’s often leisurely and prolix way, with more or less repetition, which we will condense.
The lowest animals—those destitute of a nervous system—move in response to a stimulus from without.Nature has gradually created the different organs of animals, varying the structure and situation of these organs according to circumstances, and has progressively improved their powers. She has begun by borrowing from without, so to speak—from the environment—theproductive force, both of organic movements and those of the external parts. “She has thus transported this force [the result of heat, electricity, and perhaps others (p. 307)] into the animal itself, and, finally, in the most perfect animals she has placed a great part of this force at their disposal, as I will soon show.”
This force incessantly introduced into the lowest animals sets in motion the visible fluids of the body and excites the irritability of their contained parts, giving rise to different contractile movements which we observe; hence the appearance of an irresistible propensity (penchant) which constrains them to execute those movements which by their continuity or their repetition give rise to habits.
The most imperfect animals, such as theInfusoria, especially the monads, are nourished by absorption and by “an internal inhibition of absorbed matters.” “They have,” he says, “no power of seeking their food, they have not even the power of recognizing it, but they absorb it because it comes in contact with every side of them (avec tous les points de leur individu), and because the water in which they live furnishes it to them in sufficient abundance.”
“These frail animals, in which the subtile fluids of the environingmilieuxconstitute the stimulating cause of the orgasm, of irritability and of organicmovements, execute, as I have said, contractile movements which, provoked and varied without ceasing by this stimulating cause, facilitate and hasten the absorptions of which I have just spoken.” ...
“These frail animals, in which the subtile fluids of the environingmilieuxconstitute the stimulating cause of the orgasm, of irritability and of organicmovements, execute, as I have said, contractile movements which, provoked and varied without ceasing by this stimulating cause, facilitate and hasten the absorptions of which I have just spoken.” ...
“If nature were confined to the employment of its first means—namely, of a force entirely external and foreign to the animal—its work would have remained very important; the animals would have remained machines totally passive, and she would never have given origin in any of these living beings to the admirable phenomena of sensibility, of inmost feelings of existence which result therefrom, of the power of action, finally, of ideas, by which she can create the most wonderful of all, that of thought—in a word, intelligence.“But, wishing to attain these grand results, she has by slow degrees prepared the means, in gradually giving consistence to the internal parts of animals; in differentiating the organs, and in multiplying and farther forming the fluids contained, etc., after which she has transported into the interior of these animals that force productive of movements and of actions which in truth it would not dominate at first, but which she has come to place, in great part, at their disposition when their organization should become very much more perfect.“Indeed, from the time that the animal organization had sufficiently advanced in its structure to possess a nervous system—even slightly developed, as in insects—the animals provided with this organization were endowed with an intimate sense of their existence, and from that time the force productive of movements was conveyed into the very interior of the animal.“I have already made it evident that this internal force which produces movements and actions should derive its origin in the intimate feeling of existence which animals with a nervous system possess, and that this feeling, solicited or aroused by needs, should then start into motion the subtile fluid contained in the nerves and carry it to the muscles which should act, this producing the actions which the needs require.“Moreover, every want felt produces an emotion in the inner feeling of the individual which experiences it; and from this emotion of the feeling in question arises the force which gives origin to the movement of the parts which are placed in activity....“Thus, in the animals which possess the power of acting—namely, the force productive of movements and actions—the inner feeling, which on each occasion originates this force, being excited by some need, places in action the power or force in question; excites the movement of displacement in the subtile fluid of the nerves—which the ancients calledanimal spirits; directs this fluid towards that of its organs which any want impels to action; finally makes this same fluid flow back into its habitual reservoirs when the needs no longer require the organ to act.“The inner feeling takes the place of thewill; for it is now important to consider that every animal which does not possess the special organ in which or by which it executes thoughts, judgments, etc., has in reality no will, does not make a choice, and consequently cannot control the movements which its inner feeling excites.Instinctdirects these actions, and we shall see that this direction always results from emotions of the inner feeling, in which intelligence has no part, and from the organization even which the habits have modified, in such a manner that the needs of animals which are in thiscategory, being necessarily limited and always the same in the same species, the inner feeling and, consequently, the power of acting, always produces the same actions.“It is not the same in animals which besides a nervous system have a brain [the author meaning the higher vertebrates], and which make comparisons, judgments, thoughts, etc. These same animals control more or less their power of action according to the degree of perfection of their brain; and although they are still strongly subjected to the results of their habits, which have modified their structure, they enjoy more or less freedom of the will, can choose, and can vary their acts, or at least some of them.”
“If nature were confined to the employment of its first means—namely, of a force entirely external and foreign to the animal—its work would have remained very important; the animals would have remained machines totally passive, and she would never have given origin in any of these living beings to the admirable phenomena of sensibility, of inmost feelings of existence which result therefrom, of the power of action, finally, of ideas, by which she can create the most wonderful of all, that of thought—in a word, intelligence.
“But, wishing to attain these grand results, she has by slow degrees prepared the means, in gradually giving consistence to the internal parts of animals; in differentiating the organs, and in multiplying and farther forming the fluids contained, etc., after which she has transported into the interior of these animals that force productive of movements and of actions which in truth it would not dominate at first, but which she has come to place, in great part, at their disposition when their organization should become very much more perfect.
“Indeed, from the time that the animal organization had sufficiently advanced in its structure to possess a nervous system—even slightly developed, as in insects—the animals provided with this organization were endowed with an intimate sense of their existence, and from that time the force productive of movements was conveyed into the very interior of the animal.
“I have already made it evident that this internal force which produces movements and actions should derive its origin in the intimate feeling of existence which animals with a nervous system possess, and that this feeling, solicited or aroused by needs, should then start into motion the subtile fluid contained in the nerves and carry it to the muscles which should act, this producing the actions which the needs require.
“Moreover, every want felt produces an emotion in the inner feeling of the individual which experiences it; and from this emotion of the feeling in question arises the force which gives origin to the movement of the parts which are placed in activity....
“Thus, in the animals which possess the power of acting—namely, the force productive of movements and actions—the inner feeling, which on each occasion originates this force, being excited by some need, places in action the power or force in question; excites the movement of displacement in the subtile fluid of the nerves—which the ancients calledanimal spirits; directs this fluid towards that of its organs which any want impels to action; finally makes this same fluid flow back into its habitual reservoirs when the needs no longer require the organ to act.
“The inner feeling takes the place of thewill; for it is now important to consider that every animal which does not possess the special organ in which or by which it executes thoughts, judgments, etc., has in reality no will, does not make a choice, and consequently cannot control the movements which its inner feeling excites.Instinctdirects these actions, and we shall see that this direction always results from emotions of the inner feeling, in which intelligence has no part, and from the organization even which the habits have modified, in such a manner that the needs of animals which are in thiscategory, being necessarily limited and always the same in the same species, the inner feeling and, consequently, the power of acting, always produces the same actions.
“It is not the same in animals which besides a nervous system have a brain [the author meaning the higher vertebrates], and which make comparisons, judgments, thoughts, etc. These same animals control more or less their power of action according to the degree of perfection of their brain; and although they are still strongly subjected to the results of their habits, which have modified their structure, they enjoy more or less freedom of the will, can choose, and can vary their acts, or at least some of them.”
Lamarck then treats of the consumption and exhaustion of the nervous fluid in the production of animal movements, resulting in fatigue.
He next occupies himself with the origin of the inclination to the same actions, and of instinct in animals.
“The cause of the well-known phenomenon which constrains almost all animals to always perform the same acts, and that which gives rise in man to a propensity (penchant) to repeat every action, becoming habitual, assuredly merits investigation.“The animals which are only ‘sensible’[184]—namely, which possess no brain, cannot think, reason, or perform intelligent acts, and their perceptions being often very confused—do not reason and can scarcely vary their actions. They are, then, invariably bound by habits. Thus the insects, which of all animals endowed with feeling have the least perfect nervoussystem,[185]have perceptions of objects which affect them, and seem to have memory of them when they are repeated. Yet they can vary their actions and change their habits, though they do not possess the organ whose acts could give them the means.“On the Instincts of Animals.“We define instinct as the sum (ensemble) of the decisions (déterminations) of animals in their actions; and, indeed, some have thought that these determinations were the product of a rational choice, and consequently the fruit of experience. Others, says Cabanis, may think with the observers of all ages that several of these decisions should not be ascribed to any kind of reasoning, and that, without ceasing as for that to have their source in physical sensibility, they are most often formed without the will of the individuals able to have any other part than in better directing the execution. It should be added, without the will having any part in it; for when it does not act, it does not, of course, direct the execution.“If it had been considered that all the animals which enjoy the power of sensation have their inner feeling susceptible of being aroused by their needs, and that the movements of their nervous fluids, which result from these emotions, are constantly directed by this inner sentiment and by habits, then it has been felt that in all the animals deprived of intelligence all the decisions of action can never be the result of a rational choice, of judgment, of profitable experience—in a word, of will—but that they are subjected to needs which certain sensations excite, and which awaken the inclinations which urge them on.“In the animals even which enjoy the power ofperforming certain intelligent acts, it is still more often the inner feeling and the inclinations originating from habits which decide, without choice, the acts which animals perform.“Moreover, although the executing power of movements and of actions, as also the cause which directs them, should be entirely internal, it is not well, as has been done,[186]to limit to internal impressions the primary cause or provocation of these acts, with the intention to restrict to external impressions that which provokes intelligent acts; for, from what few facts are known bearing on these considerations, we are convinced that, either way, the causes which arouse and provoke acts are sometimes internal and sometimes external, that these same causes give rise in reality to impressions all of which act internally.“According to the idea generally attached to the wordinstinctthe faculty which this word expresses is considered as a light which illuminates and guides animals in their actions, and which is with them what reason is to us. No one has shown that instinct can be a force which calls into action; that this force acts effectively without any participation of the will, and that it is constantly directed by acquired inclinations.”
“The cause of the well-known phenomenon which constrains almost all animals to always perform the same acts, and that which gives rise in man to a propensity (penchant) to repeat every action, becoming habitual, assuredly merits investigation.
“The animals which are only ‘sensible’[184]—namely, which possess no brain, cannot think, reason, or perform intelligent acts, and their perceptions being often very confused—do not reason and can scarcely vary their actions. They are, then, invariably bound by habits. Thus the insects, which of all animals endowed with feeling have the least perfect nervoussystem,[185]have perceptions of objects which affect them, and seem to have memory of them when they are repeated. Yet they can vary their actions and change their habits, though they do not possess the organ whose acts could give them the means.
“We define instinct as the sum (ensemble) of the decisions (déterminations) of animals in their actions; and, indeed, some have thought that these determinations were the product of a rational choice, and consequently the fruit of experience. Others, says Cabanis, may think with the observers of all ages that several of these decisions should not be ascribed to any kind of reasoning, and that, without ceasing as for that to have their source in physical sensibility, they are most often formed without the will of the individuals able to have any other part than in better directing the execution. It should be added, without the will having any part in it; for when it does not act, it does not, of course, direct the execution.
“If it had been considered that all the animals which enjoy the power of sensation have their inner feeling susceptible of being aroused by their needs, and that the movements of their nervous fluids, which result from these emotions, are constantly directed by this inner sentiment and by habits, then it has been felt that in all the animals deprived of intelligence all the decisions of action can never be the result of a rational choice, of judgment, of profitable experience—in a word, of will—but that they are subjected to needs which certain sensations excite, and which awaken the inclinations which urge them on.
“In the animals even which enjoy the power ofperforming certain intelligent acts, it is still more often the inner feeling and the inclinations originating from habits which decide, without choice, the acts which animals perform.
“Moreover, although the executing power of movements and of actions, as also the cause which directs them, should be entirely internal, it is not well, as has been done,[186]to limit to internal impressions the primary cause or provocation of these acts, with the intention to restrict to external impressions that which provokes intelligent acts; for, from what few facts are known bearing on these considerations, we are convinced that, either way, the causes which arouse and provoke acts are sometimes internal and sometimes external, that these same causes give rise in reality to impressions all of which act internally.
“According to the idea generally attached to the wordinstinctthe faculty which this word expresses is considered as a light which illuminates and guides animals in their actions, and which is with them what reason is to us. No one has shown that instinct can be a force which calls into action; that this force acts effectively without any participation of the will, and that it is constantly directed by acquired inclinations.”