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First Part
Considerations of the Natural History of Animals, Their Characteristics, Their Interrelationships, Their Organic Structure, Their Distribution, Their Classification and Their Species
Chapter Three
Concerning Speciation among Living Things and the Idea Which We Should Attach to This Word
It is not a futile pursuit firmly to establish the idea which we should form about what are called species among living creatures and to investigate whether it is true that species have an absolute constancy, are as old as nature, and have all existed originally just as we see them today, or whether, subject to changes which could have taken place in the circumstances relevant to them, they have not changed their characteristics and shape with the passage of time (although extremely slowly).
The illumination of this question is not only of interest to our zoological and botanical knowledge but also is essential to the history of the earth.
I will show in one of the chapters which follow that each species has received from the influence of the circumstances which it encounters over a long period the habits which we know about and that these habits have themselves exerted influences on the parts of each individual of the species, to the point where they have modified these parts and have made them appropriate to the acquired habits. Let us first examine the idea which has developed about what is called a species.
We call species every collection of similar individuals produced by other individuals just like themselves.
This definition is exact, for every individual enjoying life always resembles very closely the one or those from which it came. But we add to this definition the assumption that the individuals who make up a species never vary in their specific characteristics and that therefore the species has an absolute constancy in nature.
It is precisely this assumption that I propose to contest, because clear proofs obtained through observation establish that it is not well founded.
The assumption almost universally admitted that living things make up eternally distinct species on account of their invariable characteristics and that the existence of these species is as ancient as nature herself was established at a time when people had not observed nature sufficiently and when the natural sciences were still almost nothing. The assumption is contradicted every day in the eyes of those who have looked at a great deal and have followed nature for a long time, and who have reaped the benefits of the large and rich collections in our museum.
Moreover, all those who are very busy studying natural history know that nowadays naturalists are extremely embarrassed in their attempts to define the objects which they have to consider species. In fact, not knowing that species have a constancy only relative to the duration of the circumstances in which all the individuals composing them are found and that some of these individuals, having undergone variations, make up races which modulate into some other neighbouring species, naturalists make decisions arbitrarily, by describing some individuals observed in different countries and in various environments as varieties and others as species. As a result, that section of work concerning the determination of species is becoming day by day increasingly defective, that is, more embarrassing and confusing.
In truth, it has been observed for a long time that there exist collections of individuals who so resemble each other in their organic structure, as well as by the totality of their parts, and who remain in the same condition generation after generation for as long as we have known about them that people have believed themselves justified in regarding these collections of similar individuals as making up just as many invariable species.
Now, not having attended to the fact that the individuals of a species must perpetuate themselves without variation, as long as the circumstances which influence their manner of life do not essentially vary and the existing prejudices agreeing well enough with the successive regeneration of similar individuals, people have assumed that each species did not vary, was also as old as nature, and was uniquely created by the work of the Supreme Author of everything which exists.
There is no doubt that nothing exists except by the will of the sublime Author of everything. But can we assign some rules to Him in the execution of His will and establish the method which He followed in this matter? Could not His infinite power have been capable of creating an order of things which gave life successively to everything which we see, as well as to everything existing which we do not know about?
To be sure, whatever His will, the immensity of his power is still the same and whatever the manner in which the Supreme Will carried out His work, nothing can diminish His grandeur.
Therefore, respecting the decrees of this infinite wisdom, I confine myself within the limits of a simple observer of nature. Then, if I manage to unravel something of the progress which nature has followed to bring about its productions, I will say, without fear of being wrong, that it has pleased her Author that nature has had this faculty and this power.
The notion of species among living creatures which people formed was very simple, easy to grasp, and seemed confirmed by the constancy in the apparent form of individuals which reproduction or generation perpetuated. Such individuals create for us a great number of those alleged species which we see every day.
However, the more we advance our knowledge of the different organic bodies which cover the surface of the earth almost everywhere, the greater becomes our embarrassment about determining what ought to be regarded as a species and, for even more compelling reasons, about limitingand distinguishing genera.
The more we collect the productions of nature and our collections grow richer, the more we see almost all the gaps being filled and our lines of separation being erased. We find ourselves reduced to an arbitrary determination, which sometimes leads us to seize upon the least differences among the varieties to form the characteristic of what we call species. Sometimes this makes us call certain individuals with slight differences a variety of some species. Other people consider these individuals constitute a separate species.
Let me repeat myself: the more our collections increase, the more we encounter proofs that everything is more or less nuanced, the remarkable differences disappear, and as often as not nature makes available to us for the creation of distinctions only minute and, so to speak, puerile particularities ... .
When we formed these genera, we knew only a small number of their species; thus, they were easy to distinguish. But now that almost all the gaps between them have been filled, our specific differences are necessarily minute and very frequently insufficient.
Having well established this state of affairs, let us examine the causes which can have given rise to it. Let us see if nature possess means for that and if observation could have given us insight into this question.
A number of facts teach us that, to the extent that the individuals of one of our species change their situation, climate, manner of life, or habits, they obtain from that change influences which little by little alter the constancy and the proportions of their parts, shape, faculties, even their organic structure, with the result that everything in them participates, over time, in the mutations which they have experienced.
In the same climate, significantly different situations and exposures at first simply induce changes in the individuals who find themselves confronted with them. But as time passes, the continual difference in the situation of the individuals I’m talking about, who live and reproduce successively in the same circumstances, leads to changes in them which become, in some way, essential to their being, so that after many generations, following one after the other, these individuals, belonging originally to another species, find themselves at last transformed into a new species, distinct from the other.
For example, if the seeds of a grass or of any other plant common to a humid prairie are transported, by some circumstance or other, at first to the slope of a neighbouring hill, where the soil, although at a higher altitude, is still sufficiently damp to allow the plant to continue living, if then, after living there and reproducing many times in that spot, the plant little by little reaches the almost arid soil of the mountain slope and succeeds in subsisting there and perpetuates itself through a sequence of generations, it will then be so changed that botanists who come across it there will create a special species for it.
The same thing happens to animals which circumstances have forced to change their climate, manner of life, and habits. But for these, the causal influences which I have just mentioned require even more time than is the case with plants in order to effect notable changes in the individuals.
The idea of including, in the name species, a collection of similar individuals who perpetuate creatures like themselves through reproduction and who have thus existed in the same form for as long as nature necessarily requires that the individuals of the same species, in their reproductive acts, cannot mate with the individuals of another species.
Unfortunately, observation has demonstrated and still establishes every day that this idea has no foundation whatsoever. For hybrids, very well known among plants, and the matings which we often see between individuals of very different species among animals attest to the fact that the limits between these species, supposedly constant, were not as firm as people have imagined.
To be sure, often nothing results from these odd matings, above all when they involve very different types, and then the individuals produced are, in general, infertile. But then again, when the disparity is less great, we know that the flaws in question do not occur. Now, this method by itself is sufficient to create varieties gradually which then become races, and which, in time, make up what we call species.
In order to evaluate whether the traditional idea of species has some real foundation, let us look again at points which I have already established. They enable us to see the following:
1.All organic bodies of our earth are true products of nature, which she has brought forth successively over a long period of time;
2.In her progress, nature began, and begins again every day, by creating the simplest organic bodies, and she does not directly create anything except by this process, that is to say, by these first beginnings of organic structure which are designated by the expression spontaneous generation.
3.The first beginnings of animals and plants were formed in appropriate places and circumstances. Once the faculties of a commencing life and of organic movement were established, these animals and plants of necessity gradually developed organs, and, in time, they diversified these organs, as well as their parts.
4.The faculty of growth in each portion of an organic body is inherent in the first effects of life; it gave rise to different ways of multiplication and reproduction of individuals. In this process, the progress acquired in the composition of the organic structure and in the shape and diversity of parts was maintained.
5.With the help of a sufficient lapse of time, of circumstances which were necessarily favourable, of changes which every point on the surface of the earth has successively undergone, in a word, with the assistance of the power which new situations and habits have for modifying the organs of a body endowed with life, all those which exist now have been imperceptibly shaped just as we see them.
6.Finally, after a sequence of events like the above, living bodies have each experienced greater or lesser changes in the condition of their organic structure and their parts. What we call species have been created in this way imperceptibly and successively among them; they have a constancy which is only relative to their condition and cannot be as old as nature ... .
Chapter Seven
Concerning the Influence of Circumstances on the Actions and Habits of Animals, and the Influence of the Actions and Habits of These Living Bodies as Causes Which Modify Their Organic Structure and Their Parts
What we are now concerned with is not a rational speculation but the examination of a reliable fact, a more universal one than people think and something to which we have neglected to pay the attention it deserves. Undoubtedly this is the case because on most occasions it is very difficult to recognize. This fact consists of the influence which circumstances exert on the different living things subject to them.
In truth, for quite a long time now we have noticed the influence of the different states of our organic structure on our characteristics, inclinations, actions, and even our ideas. But it seems to me that no one has yet made known the influence of our actions and habits on our own organic structure. Now, as these actions and habits are entirely dependent on the circumstances in which we usually find ourselves, I am going to try to show how great the influence is which these circumstances exert on the general form, the condition of the parts, and even on the organic structure of living things. Thus, this chapter is going to explore this very well established fact.
If we had not had numerous occasions to recognize quite clearly the effects of this influence on certain living bodies which we have transported into entirely new environments, very different from the ones where they used to live, and if we had not seen these effects and the changes resulting from them come to light in some way under our very eyes, the important fact under discussion would have always remained unknown to us.
The influence of circumstances is truly working always and everywhere on living bodies. But what makes this influence difficult for us to perceive is that its effects become perceptible or recognizable (especially in animals) only after a long passage of time.
Before laying out and examining the proofs for this noteworthy fact (something extremely important for Zoological Philosophy), let us summarize the thread of the ideas with which we started our analysis.
In the preceding paragraphs, we have seen that it is now an incontestable fact that, when we consider the animal scale in a sense opposite to the natural direction, we find that in the groups which form this scale there exists a sustained but irregular degradation in the organic structure of animals making up the groups, an increasing simplicity in the organization of living bodies and finally a corresponding diminution in the number of faculties in these beings.
This well known fact can provide us the greatest insights into the very order which nature followed in the production of all animals which she has brought into existence. But it does not show us why animals’ organic structure, with its increasing complexity from the most imperfect right to the most improved, only displays an irregular gradation in which the range manifests a number of anomalies or gaps which have no apparent order amid their variety.
Now, in seeking out the reason for this peculiar irregularity in the growing complexity of animals’ organic structure, if we consider the results of the influences which the infinitely various circumstances in all the regions of the earth exert on the general shape, parts, and even the organic structure of these animals, then everything will be clearly explained.
In fact, it will be quite clear that the condition in which we see every animal is, on the one hand, the product of the increasing complexity in organic structure which tends to create a regular gradation and, on the other hand, the product of influences of a multitude of very different circumstances which continuously tend to work against the regularity in the gradations of the growing complexity in organization.
Here it becomes necessary that I explain what I mean by the following expression: Circumstances have an influence on the form and the organic structure of animals. What this means is that by undergoing significant change, the circumstances proportionally alter, over time, both the form and the organic structure itself
True, if someone takes these expressions literally, he would say I was making a mistake. For no matter what the circumstances can be, they do not work to bring about directly any modification whatsoever in the shape and organic structure in animals.
But significant changes in the circumstances lead, for animals, to great changes in their needs. Such changes in the needs necessarily lead to changes in their actions. Now, if the new needs become constant or last a long time, the animals then acquire new habits which are just as long lasting as the needs which brought them about. That is what is easy to demonstrate and, indeed, requires no detailed explanation to be understood.
Thus, it is clear that a significant change in circumstances, once it becomes constant for a race of animals, leads these animals to new habits ... .
In the plants where there are no actions and consequently, strictly speaking, no habits, significant changes in circumstances nonetheless lead to significant differences in the development of their parts. As a result, these different circumstances give rise to and develop certain parts, while they weaken several other parts and lead to their disappearance. But here everything exerts its effect through changes undergone in what the plant uses for nourishment, in what it absorbs and breathes, in the quality of heat, light, air, and humidity which the plant customarily then receives, and, finally, through the superiority which some of these various vital movements can gain over others.
Among individuals of the same species, if some are continually well nourished in circumstances favourable to their total development, while others find themselves in opposite circumstances, then there is produced a difference between the conditions of these individuals which gradually becomes very noticeable. How many examples I could cite concerning animals and plants which confirm the basis for this idea! Now, if circumstances remain the same, making the condition of the poorly nourished individuals habitual and constant, with suffering and malnourishment, their interior organic structure is finally changed. Reproduction among the individuals in question preserves the acquired modifications and ends up by giving rise to a race very different from the one made up of individuals who find themselves constantly in circumstances favourable to their development.
A very dry spring causes prairie grasses to grow very little, to remain thin and scrawny, to flower and bear fruit, although they have grown very little.
A spring mixed with hot days and rainy days brings about in these same grasses a generous growth, and the harvest of hay is then excellent.
But if with these plants some causes perpetuate unfavourable circumstances, they will vary proportionally, at first in their bearing or their general condition, and later in several specific characteristics.
For example, if a grain of some prairie grass or other is carried into a high place, onto a dry, arid, and rocky patch of land very exposed to the wind and can germinate there, the plant which can live in this place will always find itself malnourished, and if the individuals which it produces continue to exist in these poor circumstances, there will result a race truly different from the one which lives in the prairie (which is, however, the origin of the second race). The individuals of this new race will be small, scrawny in their parts, and some of their organs, having undergone more development than others, will then manifest strange proportions.
Those who have observed a great deal and consulted large collections have been convinced that as the conditions in the environment, exposure, climate, nourishment, way of life, and so on undergo changes, the characteristics of height, shape, proportions among the parts, colour, consistency, agility, and industry (for the animals) correspondingly change.
What nature does with a great deal of time, we do every day, when on our own we suddenly change the conditions in which a living plant and all the individuals of its species are found. ...
The following fact proves (with respect to plants) how much a change in some important circumstance has an influence on changing the parts of living organisms ... .
There is no doubt that, so far as animals are concerned, important changes in the circumstances where they usually live produce similar changes in their parts. But here the changes are much slower manifesting themselves than in the plants. Consequently, they are less perceptible to us and their cause less recognizable.
Now, the true order of things relevant to consider in all this consists in recognizing the following:
1.All slightly remarkable changes later maintained in circumstances where each race of animals is located works to create in that race a real change in its needs.
2.All changes in animals’ needs require of them alternative actions to satisfy the new needs and, consequently, alternative habits.
3.Since the satisfaction of every new need demands new actions, it requires from the animal experiencing that need either the more frequent use of some of its parts which previously it used less often (something which develops and makes that part grow), or the use of new parts which the needs imperceptibly bring forth in the animal by the efforts of its interior feeling. This I will establish very soon by known facts.
Thus, to reach an understanding of the true causes of so many diverse forms and so many different habits, examples of which the known animals manifest to us, we must take into account the fact that the infinitely diversified and slowly changing conditions in which the animals of each race are successively located have led, in each of them, to new needs and necessarily to changes in their habits. Now, once this truth, which one cannot contest, is recognized, it will be easy to see how animals have been able to satisfy the new needs and to acquire new habits, if we give some attention to the two following laws of nature, which observation has always confirmed.
First Law
In every animal which has not exceeded the limit of its development, the more frequent and sustained use of any organ gradually strengthens this organ, develops it, makes it larger, and gives it a power proportional to the duration of this use; whereas, the constant lack of use of such an organ imperceptibly weakens it, makes it deteriorate, progressively diminishes it faculties, and ends by making it disappear.
Second Law
Everything which nature has made individuals acquire or lose through the influence of conditions to which their race has been exposed for a long time and, consequently, through the influence of the predominant use of some organ or by the influence of the constant disuse of this organ, nature preserves by reproduction in the new individuals arising from them, provided that the acquired changes are common to the two sexes or to those who have produced these new individuals.
These are the two constant truths which cannot be overlooked except by those who have never observed nor followed nature in her work or by those who have let themselves be led into the error which I am going to contest.
Once naturalists noticed that the forms of animals’ parts are always linked to the use of these parts, they thought that the forms and the condition of the parts had led to the usage. Now, there is the mistake. For it is easy to demonstrate through observation that, by contrast, it is the needs and the use of the parts which have developed them, factors which even produced the parts at a time when they did not exist and which, consequently, gave rise to the condition in which we see them in each animal.
In order for that not to be the case, it would have been necessary for nature to create for the animal parts as many forms as required by the diversity of circumstances in which they have to live and that these forms, as well as the circumstances, never change.
That is certainly not the natural order which exists. If it had ever really been like that, we would not have race horses in the form of those in England; we would not have our large draught horses, so heavy and different from these race horses, for nature on her own did not produce anything like them. For the same reason we would not have basset hounds with crooked limbs, such swift-running greyhounds, water spaniels, and so on. We would not have tailless hens, fantail pigeons, and so on. Finally, we would be able to cultivate wild plants as much as we liked in the rich fertile soil of our gardens, without fear of seeing them change through long cultivation.
In this matter, for a long time we have had a feeling for what is really the case, because we developed the following sentence, which has become proverbial and universally known: habits form a second nature.
To be sure, if habits and the nature of every animal were incapable of ever changing, the proverb would be false, would not have arisen, and would not have been able to be preserved in the event someone had proposed it.
If one considers seriously everything which I have just revealed, one will sense that I grounded my views rationally when in my work entitled Research Into Living Bodies (p. 50), I laid down the following proposition:
“It is not the organs, that is, the nature and the form of the animal’s body parts, which have given rise to its habits and special faculties, but, by contrast, its habits, manner of life, and circumstances of the individuals from which the animal comes to possess, over time, the form of its body,the number and condition of its organs, and finally the faculties which it enjoys.”
Let people consider well this proposition and bring to it all the observations which nature and the state of things enable us to make all the time. Then its importance and reliability will become for us the most significant evidence.
Favourable times and circumstances are, as I have already said, the two main means employed by nature to bring into existence all her productions. We know that time has no limits for her and that, as a result, she always has time to spare.
As to the circumstances which she needed and which she still uses every day to vary everything which she continues to produce, we can say that circumstances are, in some way, for her inexhaustible.
The main circumstances arise from the influence of climates, various temperatures in the atmosphere and all the environmental surroundings, the variety of places and their exposure, habits, the most ordinary movements, the most frequent actions, finally the means of self-preservation, reproduction, and so on.
Now, as a result of these various influences, the faculties expand and grow stronger through use. With new habits preserved over a long time they diversify. Imperceptibly the arrangement, consistency, in a word, the nature and the condition of the parts, as well as the organs, undergo the consequences of all these influences, preserving and propagating themselves in reproduction.
These truths, which are only the consequences of the two natural laws set forth above, are, in every case, amply confirmed by the facts. They indicate clearly the march of nature in the variety of her productions.
But instead of contenting ourselves with generalities which we could consider hypothetical, let us examine the facts directly. Let us consider in animals what is produced by the use or lack of use of their organs on these very organs, according to the habits which each race has been compelled to acquire.
Now, I am going to prove that the constant lack of exercise with respect to an organ at first reduces its faculties, then gradually shrinks it, and ends up by making it disappear or even destroying it, if this lack of use continues for a long time in a sequence of successive generations of animals of the same race.
Then I will reveal how, by contrast, the habit of exercising an organ, in every animal which has not reached the limit in the diminution of its faculties, not only improves this organ’s faculties and makes it grow, but also makes it develop and acquire dimensions which imperceptibly change it, so that in time it makes it quite different from the same organ examined in another animal which exercises it much less.
The lack of use of an organ, once it has become constant because of the habits which one has taken up, gradually diminishes that organ and ends up by making it disappear and even destroying it.
Many insects which, according to the natural characteristics of their order and even their genus, should have wings, lack them more less completely, because they do not use them. A number of coleoptera, orthopetera, hymenoptera, and hemiptera, and so on give us examples of this fact.The habits of these animals never put them in situations where they used their wings.
But it is not sufficient to provide an explanation for the cause which has led to the state of the organs of different animals, a condition which we observe is always the same in those of the same species. In addition, it is necessary to make known the alterations brought about in the organs of a single individual during its lifetime, solely as the product of a great mutation in the habits unique to the individuals of its species. The following extremely remarkable fact will complete the proof of the influence of habits on the condition of the organs and establish how much sustained changes in the habits of an individual lead to changes in the condition of the organs which are brought into action during the exercise of these habits.
Mr. Tenon, member of the Institute, has made known to the Class of Sciences, that he examined the intestinal canal of several men who had been passionate drinkers for a large part of their lives. He constantly found the organ shortened by an extraordinary amount in comparison with the same organ in all those who had not picked up the same habit.
We know that great drinkers, or those who have been addicted to drinking, eat very little solid food, that they eat almost nothing, and that the drink which they consume in abundance and frequently is sufficient to nourish them.
Now, since the alimentary fluids, especially spirit drinks, do not stay for long either in the stomach or in the intestine, among drinkers the stomach and the rest of the intestinal canal lose the habit of being distended, just as the stomachs of sedentary persons constantly busy with intellectual work who are accustomed to eating only a little gradually over time contract, and their intestines grow shorter.
This matter is not at all a question of a shrinking and a contraction brought about by a gathering in of the parts which would allow for an ordinary extension if these internal organs were filled, rather than undergoing a sustained emptiness. It is rather a question of a real and considerable shrinkage and contraction such that these organs would break rather than yield suddenly to causes which demand an ordinary extension.
Compare, at entirely similar ages, a man who, in order to free himself for studies and habitual intellectual work, has acquired the habit of eating very little with another who habitually takes plenty of exercise, frequently goes out of his house, and eats well. The stomach of the first will have very little capacity and will be filled by a very small quantity of nourishment, while the stomach of the second will have preserved and even increased its capacity.
There we have an organ strongly modified in its dimensions and capacity by the single cause of a change in habits over the lifetime of an individual.
The frequent use of an organ, once it becomes constant and habitually, increases the capacities of this organ, develops it, and makes it acquire dimensions and an active power which the organ does not possess in the animals which exercise it less ... .
Translated by Ian Johnston
Reading and Discussion Questions
1.What assumption about species is Lamarck contesting in this reading? What evidence does he provide in support of his own view?
2.By what mechanisms does Lamarck believe living things change over time?
3.Lamarck believes that organisms are constantly (if gradually) increasing in complexity, and that the earth is very old. How then, does he explain the continued existence of simple organisms on the earth?