Zoological Philosophy
J. B. Lamarck

[This translation, which has been prepared by Ian Johnston of Malaspina University-College, Nanaimo, BC, Canada, (now Vancouver Island University) is in the public domain, and may be used by anyone, in whole or in part, without permission and without charge, provided the source is acknowledged, released September 1999]

Table of Contents

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 limiting and 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.

How many genera, among animals and plants, are so extensive in the quantity of species which people assign to them, that the study and the definition of these species are now almost unworkable! The species in these genera, arranged in a series and set beside each other according to an analysis of their natural affinities, display, along with those which are close to them, differences so slight that they are modifications of each other and these species get confused, in some way, amongst each other, leaving almost no way of determining in some explicit way the small differences which distinguish them.

Those who have concerned themselves long and diligently with the determination of species and who have looked at rich collections are the only ones who can know at what point, among living things, species merge into each other and who could convince themselves that, in those places where we see isolated species, the phenomenon occurs only because we are missing other closely related species which we have not yet collected.

For all the above remarks, I do not wish to state that existing animals form a very simple series, equally modified throughout. But I do say that they form a branching series, with irregular gradations, something which has no discontinuity in its parts or which, at least, has not always had them, if it is true that as a result of some lost species such discontinuity occurs here and there. From this it follows that species which end each branch of this general series have, at least on one side, other closely related species which meld into them. This well known state of things leads me now to provide an illustration.

I do not require any hypothesis nor any assumption for such a demonstration. I call all observing naturalists to vouch for its truth.

Not only many genera but some entire orders and sometimes even the classes already offer us almost complete sections of the state of things which I am going to point to.

Now, when, in this example, one arranges the species in a series, placing them correctly following their natural affinities, if you choose one and then, making a jump over several others, take another species a little distant, these two species, when compared, will present to you major differences between them. This was the manner in which we started to see nature’s productions which we find most frequently within reach. Then the generic and specific distinctions were very easy to establish. But now that our collections are extremely profuse, if you follow the series which I have cited immediately above from the species you first chose right up to the one which you selected second (which is very different from the first), you will reach that second species through a series of slight modifications without having noticed distinctions worthy of attention.

Here is the question: What experimental zoologist or botanist has not explored the basis of what I have just revealed?

How then are we to study species or how are we able to determine them with a reliable method, among this multitude of polyps of all the orders, radiates, worms, and, above all, insects, where the individual order butterfly, Phalaena, Noctua, Tinea, flies, Ichneumon, Curculio, Cerambix, chafers, rose-chafers, and so on and so on already display so many closely related species, modifying into and almost overlapping each other?

What a crowd of shell creatures the mollusks show us from all countries and all seas, eluding our ways of distinguishing them and wearing out our resources on this question.

Go back up to the fish, reptiles, birds, even to mammals. You will see everywhere, apart from the gaps which still have to be filled, the modifications which link up neighbouring species, even genera, leaving hardly any places for our ingenuity to establish good distinctions.

And in its various parts does not botany, which focuses on the other series making up the plants, display exactly the same state of things?

In fact, what difficulties are not experienced nowadays in studying and determining species in the genera Lichen, Fucus, Carex, Poa, Piper, Euphorbia, Erica, Hieracium, Solanum, Geranium, Mimosa, and on and on?

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.

But, someone will say, when people want to assume that with the help of a great deal of time and an infinite variation in circumstances, nature has gradually formed the various animals which we know about, would they not have this assumption challenged by the single consideration of the admirable diversity which we see in the instincts of these different animals and by the consideration of the marvels in every genus which their various sorts of work offer?

Dare one carry the systematic spirit so far as to say that it is nature alone which has created this astonishing diversity of means, tricks, dexterity, precaution, and patience, so often illustrated to us by the industry of animals? Is not what we observe in this respect in the class of insects alone a thousand times more than sufficient to make us feel that limiting the power of nature would not permit her to produce on her own so many marvels and to impress on us the most persistent belief that here the will of the supreme Author of everything was necessary and alone sufficed to bring into existence so many admirable things?

Without doubt, one would have to be foolhardy or rather entirely idiotic to claim to assign limits to the power of the first Author of everything. But, by that alone, no one can dare to say that this infinite power could not have willed what nature herself shows us it has willed.

This being the case, if I discover that nature herself brings about all these wonders which have just been mentioned, that she has created organic structures, life, even feeling, that she has multiplied and diversified within limits which we do not know, the organs and faculties of organic bodies in whom she supports and propagates existence, that she has created in animals, by the sole route of needs, which establish and direct habits, the source of all actions, all faculties, from the simplest right up to those which make up instinct, work, and finally reasoning, must I not recognize in this power of nature, that is to say, in the order of existing things, the work of the will of her divine Author, who has been able to will that she has this ability?

Will I admire less the grandeur of the power of this first cause of everything if it has pleased Him that things were like this, that if, by so many acts of His will, this power was occupied and still is continually occupied with the details of all the particular things of creation, all the variations, all the developments and improvements, all the destruction and all the renewals, in a word, of all the transformations which universally happen in existing things?

Now, I hope to prove that nature possesses the means and the abilities necessary for her to produce by herself what we admire in her.

However, another objection is that everything which we see announces, concerning the condition of living things, an unalterable constancy in the conservation of form. And it is believed that all the animals whose history has been handed down to us in the past two or three thousand years have always been the same and have lost nothing and acquired nothing in the improvement of their organs and in the shape of their parts.

Moreover, in order to give this apparent stability over a long period the status of a verified fact, an attempt has just been made to provide particular written proofs for it in the Report On the Collections of Natural History Brought Back from Egypt by M. Geoffroy. Those writing the report express themselves on this point in the following way:

“First, the collection has this remarkable quality, that we can say it contains animals of all centuries. For a long time now, people have wanted to know if species change their form with the passage of time. This apparently futile question is essential to the earth’s history and, consequently, to the solution of a thousand other questions, which are not irrelevant to the most serious purposes of human reverence.

We have never been in a better position to make a decision about a large number of remarkable species and for several thousands of others. It appears that the superstition of the ancient Egyptians was inspired by nature, with a view to leaving a monument of her history. . . .

“It is not possible, the writers of the report continue, to control one’s imaginative excitement when one sees still preserved with the smallest bones, the smallest hairs, and perfectly recognizable, such an animal which had, two or three thousand years ago, priests or altars in Thebes or Memphis. But without losing ourselves in all the ideas which this link generates, let us limit ourselves to revealing to you that, as a result of this part of Geoffroy’s collection, these animals are perfectly similar to today’s.” Annales du Muséum d’Hist. natur., vol. I, p. 235, and 236.

I do not deny the conformity in the appearance of these animals with individuals of the same species alive today. Thus, the birds which the Egyptians adored and embalmed, two or three thousand years ago, are still totally similar to those which live at present in that country.

It would surely be really odd if the case was otherwise. For the situation of Egypt and its climate are still to a very large degree what they were at that period. Now, the birds which live there at present are still in the same circumstances where they were then and could not have been forced to change their habits.

Moreover, who does not sense that birds, which can so easily move on and choose places agreeable to them, are less subject to variation in local circumstances than many other animals and thus less challenged in their habits.

In fact, there is nothing in the observation mentioned above which contradicts the ideas I have revealed in this matter and, above all, which proves that the animals under discussion have existed for all time in nature. It proves only that they were present in Egypt two or three thousand years ago. And anyone in the habit of thinking about things, while at the same time observing what nature shows us of the monuments to its own antiquity, easily appreciates the value of a duration of two or three thousand years in comparison with that antiquity.

In addition, we can be sure that this apparent stability of things in nature will always be taken by common opinion as the truth of things, because, in general, people do not judge anything except in relation to themselves.

For the man who, in this matter, judges only according to changes which he perceives himself, the intervals between these mutations are conditions of stability which appear unlimited to him, because of the brevity of the lifetime of the individuals in his species. Moreover, since the records of his observations and the factual notes which he has been able to enter into his accounts go back only a few thousand years, a length of time infinitely great compared with him, but extremely small compared to durations which have witnessed the occurrence of the great changes the surface of the earth has undergone, everything appears stable on the planet which he inhabits, and he is encouraged to dismiss the signs presented to him everywhere by the monuments piled up around him or buried in the soil under his feet as he walks.

Quantities of space and time are relative. If man really wishes to imagine this truth, then he will be reserved in his judgments about the stability which he attributes in nature to the state of things which he observes. See in my Recherches sur les corps vivans, l’appendice, p. 141.

In acknowledging the imperceptible changes in species and the modification which individuals undergo, to the extent that they are forced to vary their habits or to acquire new ones, we are not confined solely to a consideration of the very small extents of time which our observations can include to allow us to see these changes. For, in addition to this induction, a number of facts collected for many years now also illuminate the question which I am examining, in such a way that it does not remain uncertain. And I can say that nowadays our observational knowledge is too advanced for the answer we are looking for not to be obvious.

In addition the fact that we know about the influences and the results of heterogeneous reproduction, we certainly know nowadays that a forceful and sustained change in the environment and in the habits and ways of life of animals works to bring about, after a suitable length of time, a very remarkable change in the individuals exposed to it.

The animal which lives freely in the plains where it habitually runs quickly and the bird which meets its needs as it continually crosses huge expanses in the air, when caged up, one in the compartments of a menagerie or in our stables, the other in our cages or in our poultry yards, there undergo over time significant influences, especially after a sequence of reproductive cycles in a condition which makes them acquire new habits.

In that new location, the first loses a large part of its lightness and agility. Its body becomes more dense; its limbs lose power and suppleness, and its faculties are no longer the same. The second becomes heavy, hardly knows how to fly any more, and acquires more flesh in all its parts.

In the sixth chapter of this first part, I will have occasion to prove by well known facts the power of changes in circumstances to give animals new needs and to lead to new actions, the power of repeated new actions to bring about new habits and new tendencies, and finally, the power of the more or less frequent use of this or that organ to modify that organ, whether by making it stronger, developing and enlarging it, or by making it more feeble, diminishing and weakening it, and even making it disappear.

In the case of plants, we will see the same thing concerning the effects of new circumstances on their manner of living and on the condition of their parts. The result is that we will no longer be astonished to see the considerable changes which we have made in those plants we have cultivated for a long time.

Thus, among living things, nature, as I have already said, offers us in an indisputable manner only individuals which succeed each other in sequence one after the other in reproduction and which come from each other. But species among them have only a relative constancy and are not invariable except temporarily.

Nevertheless, to facilitate our study and our knowledge of so many different bodies, it is useful to give the name species to the entire collection of similar individuals which reproduction perpetuates in the same condition, as long as their living circumstances do not change sufficiently to vary their habits, characteristics, and shape.

On Species Which Have Been Called Lost

There is still for me the issue of knowing if the means which nature adopted to assure the conservation of species or races has been so inadequate that entire races have now been wiped out or lost.

However, the fossil remains which we find buried in the soil in so many different places present us with the remains of a multitude of various animals which have existed. Among them there are found only a very small number who, to our knowledge, have analogous creatures like them now alive.

From that, can we logically conclude that the species which we find in the fossil state and for which there is no living individual exactly similar known to us does not exist any more in nature? There are still so many portions of the earth’s surface into which we have not gone, so many others which people capable of making observations have not crossed except casually, and still so many others, like the different parts of the sea bottom, where we have few means for identifying the animals which live there, that these different places could well conceal species unknown to us.

If there are some species truly lost, this can only be, without any doubt, among the large animals which live in the dry parts of the earth where man, through the absolute dominion which he exerts, has been able to succeed in destroying all the individuals of some species which he did not wish to preserve or to reduce to domesticity. Hence arises the possibility that the animals of Cuvier’s genera palaeotherium, anoplotherium, megalonix, megatherium, mastodon and some other species of genera already known exist no longer in nature. However, that is only a possibility.

But the animals which live in the watery depths, above all in ocean waters, as well as all the small-bodied species living on the surface of the earth and breathing air are protected against the destruction of their species at the hand of man. Their reproductive rate is so large and the means which they have to save themselves from his pursuits or traps are such that there is no evidence that he can destroy the entire species of any of these animals.

Thus, it is only the large terrestrial animals which can be exposed to destruction of their species at the hand of man. Such an event could have taken place. But its reality has not yet been completely proved.

However, among the fossil remains which we find of so many animals who have existed there is a very large number belonging to animals for whom totally similar living analogues are unknown. And among these, most belong to the shelled mollusks, so that only the shells remain of these animals.

Now, if a number of these fossil shells reveal differences which do not permit us, according to accepted opinions, to regard them as analogous to neighbouring species which we know about, surely it must follow that these shells belong to species truly lost? Why, moreover, would they be lost, since man could not have brought about their destruction? On the contrary, might it not be possible that the fossil individuals in question belong to species still existing but which have changed over time and have given way to species presently living which we find near by? The considerations which follow and our observations in the course of this work will make this assumption highly probable.

Every informed observer knows that nothing is constantly in the same state on the surface of the earth. In time, everything there undergoes various changes more or less constantly. High places are continuously eroded by the alternating actions of the sun, rain, and still other causes. Everything detached from there is drawn away toward places lower down. The beds of streams, rivers, even the seas vary in their shape, depth, and imperceptibly move. In a word, everything on the surface of the earth changes its position, shape, nature, and aspect, and even the climates of the earth’s various regions are not any more stable.

Now, if, as I will be attempting to reveal, variations in the circumstances of living things, above all for animals, lead to changes in needs, habits, and ways of life, and if these changes give rise to modification of or developments in their organs and the shape of their parts, we must sense that imperceptibly all living bodies whatsoever must vary, especially in their shapes or external characteristics, although this variation will become noticeable only after a considerable time.

Thus, it is not astonishing if, among the numerous fossils which we find in all the dry places of the earth and which present to us so many animals which existed in previous times, there are found so few whose living analogues we recognize.

By contrast, if there is anything which should astonish us it is to encounter among these numerous fossil remains of bodies once living some still having living analogues we do know about. This fact, which our fossil collections confirm, should lead us to assume that the fossil remains of animals whose living analogues we know about are the least ancient fossils. The species to which each of them belongs has undoubtedly not yet had sufficient time to vary in some of its forms.

Naturalists who have not perceived the changes which most animals experience with the passage of time, wishing to explain the facts relevant to the observed fossils, as well as to the known revolutions in different places on the surface of the earth, have assumed that a universal catastrophe took place with respect to the terrestrial globe and destroyed a large number of the species then in existence.

It is a pity that this convenient method of dealing with one’s embarrassment when one wants to explain the operations of nature whose causes one been unable to grasp has no foundation except in the imagination which created it. It cannot be supported with a single proof.

Local catastrophes, like those which produce earthquakes, volcanoes, and other particular causes are sufficiently well known, and it is possible to observe the disorder which they bring about in the places which have experienced them.

But why should anyone assume, without proof, a universal catastrophe, when the better known progress of nature is sufficient to provide a reason for all the facts which we observe in all its parts?

If one considers, on the one hand, that in everything which nature brings about, she make nothing abruptly and everywhere works slowly and by successive degrees and, on the other hand, that the particular or local causes of disorders, revolutions, displacements, and so on, can provide reasons for everything which we observe on the surface of the earth and are nonetheless subject to nature’s laws and her general progress, one will recognize that it is not at all necessary to assume that a universal catastrophe came to knock over everything and destroy a large part of the very operations of nature.

That is enough on an issue which is readily comprehensible. Let us now consider the general features and the essential characteristics of animals.


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