Lamarck, the Founder of Evolution Part 27

In the sixth chapter the author treats of the degradation and simplification of the structure from one end to the other of the animal series, proceeding, as he says, inversely to the general order of nature, from the compound to the more simple. Why he thus works out this idea of a general degradation is not very apparent, since it is out of tune with his views, so often elsewhere expressed, of a progressive evolution from the simple to the complex, and to his own cla.s.sification of the animal kingdom, beginning as it does with the simplest forms and ending with man. Perhaps, however, he temporarily adopts the prevailing method of beginning with the highest forms in order to bring out clearly the successive steps in inferiority or degradation presented in descending the animal scale.

We will glean some pa.s.sages of this chapter which bear on his theory of descent. Speaking of the different kinds of aquatic surroundings he remarks:

"In the first place it should be observed that in the waters themselves she [Nature] presents considerably diversified circ.u.mstances; the fresh waters, marine waters, calm or stagnant waters, running waters or streams, the waters of warm climates, those of cold regions, finally those which are shallow and those which are very deep, offer many special circ.u.mstances, each of which acts differently on the animals living in them. Now, in a degree equal to the make-up of the organization, the races of animals which are exposed to either of these circ.u.mstances have been submitted to special influences and have been diversified by them."

He then, after referring to the general degradation of the Batrachians, touches upon the atrophy of legs which has taken place in the snakes:

"If we should consider as a result of _degradation_ the loss of legs seen in the snakes, the _Ophidia_ should be regarded as const.i.tuting the lowest order of reptiles; but it would be an error to admit this consideration. Indeed, the serpents being animals which, in order to hide themselves, have adopted the habit of gliding directly along the ground, their body has lengthened very considerably and disproportionately to its thickness. Now, elongated legs proving disadvantageous to their necessity of gliding and hiding, very short legs, being only four in number, since they are vertebrate animals, would be incapable of moving their bodies. Thus the habits of these animals have been the cause of the disappearance of their legs, and yet the _batrachians_, which have them, offer a more degraded organization, and are nearer the fishes" (p. 155).

Referring on the next page to the fishes, he remarks:--

"Without doubt their general form, their lack of a constriction between the head and the body to form a neck, and the different fins which support them in place of legs, are the results of the influence of the dense medium which they inhabit, and not that of the _degradation_ of their organization. But this modification (_degradation_) is not less real and very great, as we can convince ourselves by examining their internal organs; it is such as to compel us to a.s.sign to the fishes a rank lower than that of the reptiles."

He then states that the series from the lamprey and fishes to the mammals is not a regularly gradated one, and accounts for this "because the work of nature has been often changed, hindered, and diverted in direction by the influences which singularly different, even contrasted, circ.u.mstances have exercised on the animals which are there found exposed in the course of a long series of their renewed generations."

Lamarck thus accounts for the production of the radial symmetry of the medusae and echinoderms, his _Radiaires_. At the present day this symmetry is attributed perhaps more correctly to their more or less fixed mode of life.

"It is without doubt by the result of this means which nature employs, at first with a feeble energy with _polyps_, and then with greater developments in the _Radiata_, that the radial form has been acquired; because the subtile ambient fluids, penetrating by the alimentary ca.n.a.l, and being expansive, have been able, by an incessantly renewed repulsion from the centre towards every point of the circ.u.mference, to give rise to this radiated arrangement of parts.

"It is by this cause that, in the Radiata, the intestinal ca.n.a.l, although still very imperfect, since more often it has only a single opening, is yet complicated with numerous radiating vasculiform, often ramified, appendages.

"It is, doubtless, also by this cause that in the soft Radiates, as the medusae, etc., we observe a constant isochronic movement, movement very probably resulting from the successive intermissions between the ma.s.ses of subtile fluids which penetrate into the interior of these animals and those of the same fluids which escape from it, often being spread throughout all their parts.

"We cannot say that the isochronic movements of the soft Radiates are the result of their respiration; for below the vertebrate animals nature does not offer, in that of any animal, these alternate and measured movements of inspiration and expiration.

Whatever may be the respiration of Radiates, it is extremely slow, and is executed without perceptible movements" (p. 200).

_The Influence of Circ.u.mstances on the Actions and Habits of Animals._

It is in Chapter VII. that the views of Lamarck are more fully presented than elsewhere, and we therefore translate all of it as literally as possible, so as to preserve the exact sense of the author.

"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 which has not received the attention it deserves, doubtless because, very often, it is quite difficult to discover.

This fact consists in the influence which circ.u.mstances 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 circ.u.mstances in which we habitually find ourselves, I shall try to show how great is the influence which these circ.u.mstances 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 circ.u.mstances, 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 circ.u.mstances 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 zoological 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 considering the 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 (_degradation_) 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 circ.u.mstances 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 mult.i.tude of very different circ.u.mstances 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 expression _circ.u.mstances 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.

"a.s.suredly, if these expressions should be taken literally, I should be accused of an error; for whatever may be the circ.u.mstances, they do not directly cause any modification in the form and structure of animals.

"But the great changes in the circ.u.mstances 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 a.s.sume new _habits_, 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 circ.u.mstances having become constant in a race of animals leads these animals into new habits.

"Now, if new circ.u.mstances, having become permanent in a race of animals, have given to these animals new _habits_--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 circ.u.mstances and 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 circ.u.mstances 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 a.s.sume over others.

"Between individuals of the same species, some of which are constantly well nourished, and in circ.u.mstances favorable to their entire development, while the others live under reversed circ.u.mstances, 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 circ.u.mstances 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 circ.u.mstances favorable to their development.

"A very dry spring-time is the cause of the gra.s.s 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 gra.s.s grow rapidly, and the harvest of hay is then excellent.

"But if any cause perpetuates the unfavorable circ.u.mstances 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 gra.s.ses 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 circ.u.mstances, 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 circ.u.mstances 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 circ.u.mstances 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 naturally very hairy then become glabrous, or almost so; many of those which were creeping and trailing, then become erect; others lose their spines or their p.r.i.c.kles; others still, from the woody and perennial condition which their stem possesses in a warm climate, pa.s.s, 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 circ.u.mstances 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 (_Tritic.u.m 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 circ.u.mstances 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 decided change 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 circ.u.mstance 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 circ.u.mstance 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 circ.u.mstances, united and becoming constant, would insensibly form a new and special race.

"Where do we find, in nature, this mult.i.tude of races of _dogs_, 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 gradually dispersed 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 (_generation_) has given rise successively to all those we now know.