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 Four

General Observations Concerning Animals

Generally considered, animals include living beings truly remarkable for faculties unique to them and at the same time worthy of our admiration and study. These beings, infinitely diversified in their forms, organic structures, and faculties, are capable of movement or of moving certain parts without the impetus of any communicated movement but by a cause which stimulates their irritability, a cause which, in some, is produced from within and, in others, is entirely outside them. For the most part, animals enjoy the ability to change their location, and they all possess eminently irritable parts.

We observe that in moving about some animals crawl, march, run, or jump, while others fly, raising themselves in the air and travelling through different spaces. Others, living in the depths of the waters, swim and transport themselves to different areas in the expanse of the surroundings waters.

The animals are not, like the plants, in a situation where they find within range right next to them the material on which they feed. Among animals, even those which live by seizing prey must go seek it out, follow it, and finally seize it. Thus, they must have a faculty of motion and even of moving around so as to be able to obtain the nourishment which they require.

Moreover, those animals which multiply by sexual reproduction do not offer sufficiently perfect hermaphrodites to enable them to meet their needs, and thus it is again necessary that they can move around to put themselves in a situation where they can reproduce. For those animals which, like the oysters, cannot change their positions, the environmental surroundings must provide means for such movement.

Thus, these needs have the capacity to provide the faculty which the animals possess of moving parts of their bodies and of carrying out movements advantageous to their own conservation and that of their race.

In the second part we will look into the source of this astonishing faculty, as well as the cause of the most remarkable which we find among them. But in the meantime, so far as the animals are concerned, we will state that it is easy to recognize the following points:

(1) Some do not move or move their parts only as a consequence of their stimulated irritability. But they do not experience any feeling and cannot have any sort of will power. These are the most imperfect animals.

(2) Others, apart from movements which their parts can undergo through their stimulated irritability, are susceptible to experiencing sensations and possess an intimate and very obscure feeling of their existence. But they act only through an interior impulse by a tendency which draws them to some object or other, so that their will power is always dependent and led on.

(3) Still other animals not only experience movements in some parts as a result of their stimulated irritabilty, are susceptible to receiving sensations, and enjoy an inner feeling of their existence, but, in addition, have the ability to form ideas for themselves, although confused, and to act by a determining will power, which is nevertheless subject to tendencies which carry them, once again, exclusively towards certain particular objects.

(4) Finally, some other animals, the most perfect, possess to a high degree all the abilities of the preceding ones and enjoy, in addition, the power of forming for themselves clear or precise ideas of objects which have affected their sense and drawn their attention, of comparing and combining these ideas up to a certain point, and deriving from them judgments and complex ideas. In a word, they have the ability to think and to have a less captive will power, which permits them to vary their actions to a greater or lesser extent.

In the least perfect animals, life is without energetic movements, and irritability alone is then sufficient for vital movements. But since vital energy increases in proportion to the complexity of organic structures, there comes a limit where in order to provide sufficiently for the activities essential to vital movements, nature had to add to its means. And for that reason, she used muscular action to establish a system of circulation, from which followed the acceleration of the movements of fluids. This acceleration itself later grew in proportion to the muscular power which it required. Finally, since no muscular activity can take place without the action of nerves, the latter were everywhere found necessary to the acceleration of the fluids in question.

In this way nature was capable of adding to the irritability, once insufficient, muscular action and neural influence. But this neural influence which gives rise to muscular action never brings it about by the path of feeling, something I hope to demonstrate in the second part. Later I will establish there that feeling is not at all necessary for the carrying out of vital movements, even in the most perfect animals.

Thus, the different existing animals are clearly distinguished from each other, not only by the particular features of their external shape, the consistency of their bodies, their size, and so on, but, in addition, by the faculties with which they are endowed. Some, like the most imperfect, find themselves reduced, in this respect, to the most limited state, not having any faculties other than those appropriate for life, not moving except through a power outside themselves; whereas, the others have progressively more numerous and more eminent faculties, to the point where the most perfect display a collection of faculties exciting our admiration.

These astonishing facts cease to surprise us when we first recognize that each acquired faculty is the result of a special organ or system of organs which gives rise to it and when later we see that from the most imperfect animal, which has no particular organ whatsoever and consequently no other faculty that those which belong to life itself, right up to the most perfect animal, the most richly endowed with faculties, the organic structure gradually gets more complex, in such a way that all the organs, even the most important, arise one after the other through the extent of the animal ladder, then successively perfect themselves by the modification which they undergo and which accommodates them to the state of their organic structure of which they are a part. Finally, through their combination in the most perfect animals they present the most complex organic structures, which produce the most numerous and most eminent faculties.

Considering the internal organic structure of animals, the different systems which this organic structure presents throughout the extent of the animal ladder, and finally, the various specialized organs is thus the most important of all the ideas which must direct our attention in the study of animals.

If animals, looked upon as productions of nature, are living beings particularly astonishing for their faculty of movement, a large number of them are considerably more astonishing for their faculty of feeling.

But just as this faculty of movement is very limited in the most imperfect animals, where it is not at all voluntary and where it does not occur except through external stimuli, so it improves later more and more. It succeeds in originating within the animal itself and finishes by being subject to the animal’s will power. Similarly the faculty of feeling is also very obscure and limited in the animals where it begins to occur, so that it develops progressively later and, having attained its main development, it manages to bring into existence in the animal the faculties which constitute intelligence.

In fact, the most perfect animals have simple and even complex ideas, passions, memory, a source of dreams, that is to say, they experience involuntary returns of their ideas, even their thoughts, and are up to a certain point capable of instruction. How admirable a result of nature’s power this is!

To succeed in giving a living body the ability to move itself without the impetus of a communicated force, to perceive objects beyond itself, to form ideas for itself, by comparing the impressions which it has recieved from them with those which it was able to receive from other objects, to compare or combine these ideas, and to produce judgments which are for it ideas of another order, in a word, to think, that is not only the greatest marvel which the power of nature has been able to achieve but, in addition, it is the proof that a considerable time has been taken up, for nature achieves nothing except step by step.

Compared to the lengths of time which we consider great in our ordinary calculations, it has undoubtedly required an enormous length of time and considerable variation in the sequence of circumstances for nature to have been able to lead the organic structure of animals to the degree of complexity and development where we see it in those who are the most improved. Thus, we justified in thinking that, if the analysis of these varied and numerous strata making up the exterior crust of the earth is an indisputable testament to its great age and if a consideration of the very slow but continuous displacement of the sea basin (1), as evidenced by the numerous monuments to its passage which it has left everywhere, confirms once again the prodigious antiquity of the terrestrial globe, then a consideration of the degree of improvement which the organic structures of most animals must have reached helps, in its turn, to provide the highest quality evidence of this truth.

But in order to establish firmly the basis of this new proof, it will be necessary first to bring fully to light the proof relevant to the progress in organic structures themselves. It will be necessary to ascertain, if possible, the reality of this progress. And finally it will be necessary to collect the best established facts in this matter and to indicate the means which nature possesses to give to all its productions the existence which they enjoy.

Let us note, meanwhile, that although it is generally acceptable, in referring to the beings which make up each kingdom, to indicate them under the general term productions of nature, it nevertheless appears that people have no clear idea associated with this expression. It seems that the prejudice against a particular origin prevents us from recognizing that nature possesses the ability and all the means to bring to life so many different beings on her own, continually to vary, although very slowly, the races of those which enjoy life, and to maintain throughout the general order which we observe.

Let us leave aside all opinions whatsoever concerning these important matters, and so as to avoid all imaginative errors, let us consult throughout the very acts of nature.

In order to be able to include, in our thinking, all existing animals and to place these animals in a perspective easy to grasp, it is appropriate to recall that all the natural productions which we can observe have been divided up by naturalists, for a long time now, into three kingdoms, under the denominations animal kingdom, vegetable kingdom, and mineral kingdom. By this division, the entities comprising each of these kingdoms have been set up comparatively, as if on the same line, although some have an origin very different from others.

For a long time now, I have found it more convenient to use another primary division, because it is appropriate for making us more aware in general terms of all the entities which are the purpose of the enquiry. This, I separate all the natural productions comprising the three kingdoms which I have just pointed out into two main branches, as follows:

(1) organically structured bodies which are alive;
(2) raw bodies without life.

Existing beings, or living bodies, like the animals and plants, make up the first of these two branches of the productions of nature. These beings have, as everyone knows, the ability to feed themselves, develop, reproduce, and are necessarily subject to death.

But what people do not so readily know, because prevailing hypotheses do not allow them to believe it, is that living bodies, as a result of their organic action and faculties, as well as the mutations which bring about in them organic movements, form themselves their own substance and secretory material (Hydrogéologie, p. 112). What people understand even less is that through their remains these living bodies give rise to the existence of all the composite materials, raw or inorganic, which we observe in nature. The various types of this material multiply in nature over time according to the circumstances of their location, through changes which they undergo imperceptibly and which simplify them more and more and lead, after a great deal of time, to the complete separation of the main elements composing them.

These are the various raw non-living materials, solid or liquid, which comprise the second branch of the productions of nature and which, for the most part, are known under the name minerals.

One can say that between raw materials and living bodies there is an immense hiatus which does not allow us to rank on the same line these two sorts of bodies, nor to undertake to link them by any modification, something which has been attempted but in vain.

All the known living bodies divide themselves neatly into two particular kingdoms, based on essential differences which distinguish animals from plants. In spite of what people have said about this, I am convinced that there is no longer a real point of subtle melding between these two kingdoms and that, consequently, that there are no animal-plants (something expressed in the word zoophyte) nor plant-animals.

The irritability in all or in certain parts is the most general characteristic of animals. That is more common than the faculty of voluntary movements and of feeling, more even that that of guiding oneself. Now, all the plants, without omitting even the plants called sensitive, nor those which move certain of their parts at the first touch or at the first contact with air, completely lack irritability. I have observed this point elsewhere.

We know that irritability is a faculty essential to the parts or some of them in animals. The actions of irritability are never suspended or destroyed so long as the animal is alive and the irritable part has not suffered any lesion in its organic structure. The effect of irritability consists of a contraction which the entire irritable part undergoes instantaneously on contact with a foreign body. The contraction stops with the cause and comes again, after the relaxation of the part, when new contacts happen to irritate it. Now, nothing like this has ever been observed in any part of plants.

When I touch the extended branches of a sensitive (mimosa pudica), instead of a contraction, I observe immediately in the attachments of the branches and disturbed petioles, a relaxation which allows these branches and petioles of the leaves to collapse, something which makes even the leaflets in this case droop down on one another. Once this drooping occurs, it is a waste of time to touch the branches and the leaves of the plant again; the effect does not recur. A relatively long time is needed, unless it is very hot, for the cause which can swell the articulations of the small branches and the leaves of the sensitive to raise again and extend all its parts and to deal with the sagging in such a way that it can happen again through contact or a light tremor.

I do not recognize in this phenomenon any connection with irritability in animals. But I do know that with plants during periods of growth, above all when it is hot, a great deal of elastic fluid is created, some of which is exhaled constantly. Thus I have concluded that in leguminous plants, these elastic fluids can gather particularly in the articulations of the leaves before dissipating and that they can there strain these joints and extend out the leaves or leaflets.

In such a case, the slow dissipation of the elastic fluids we are talking about, stimulated in the legumes by the arrival of night or the sudden dissipation of the same fluids stimulated in the mimosa pudica by a small tremor gives rise, in the legumes generally, to the phenomenon known by the term plant sleep and in the sensitive to what people attribute incorrectly to irritability (2). Since, as a consequence of observations which I reveal further on and the conclusions I have drawn from them, it is not generally true that animals are feeling beings, all endowed, without exception, with the power of making voluntary acts and, consequently, having the option of moving at their own will, the definition which has been given of animals up to the present to distinguish them from plants is totally inappropriate.  Thus I have already proposed to substitute for it the following, on the ground that it conforms more closely to the truth and is more appropriate for characterizing the beings which constitute both kingdoms of living bodies.

Definition of Animals

Animals are living organic bodies, endowed with permanently irritable parts; almost all of them digest the food with which they are nourished, and being subject to motion, some as a result of will power, whether free or dependent, and others as a result of their stimulated irritability.

Definition of Plants

Plants are living organic bodies, never having irritable parts, not digesting anything, and not subject to motion, either by will power or by real irritability.

In accordance with these definitions, which are much more precise and better grounded than those which have been used up to now, we are aware that animals are preeminently distinguished from plants by the irritability which manifests itself in all their parts or some of them and by the movements which they can produce in these parts or which are stimulated there, thanks to their irritability, by external causes.

Undoubtedly it would be wrong to accept these new ideas on the basis of a simple introduction. But I think that all unprejudiced readers who take into consideration the facts which I will lay out in the course of this work and my observations concerning them will be unable to deny that they are better that the ancient views which I am replacing with them, because these ancient ideas are obviously contradicted by everything we observe.

Let us conclude these general opinions on animals with two quite curious considerations. The first concerns the extreme multiplicity of animals on the surface of the earth and those found in the depths of the waters. The second deals with the means which nature employs so that their number never harms the preservation of what she has produced or the general order which must prevail.

Among the two kingdoms of living bodies, the one which consists of animals appears much richer and more diverse than the other; at the same time it is the kingdom which presents, in its organically structured products, the most admirable phenomena.

The surface of the earth, the depths of the waters, and, in some sense, even the air, are inhabited by an infinite number of various animals, whose races are so diversified and numerous that it is probable a large part of them will always elude our research. There is even more reason to think this given that the enormous extent of the waters, their depth in a great many places, and the prodigious fecundity of nature in the smallest spaces will undoubtedly always be an almost invincible obstacle to the advancement of our understanding of the subject.

For instance, one class of invertebrate animals by itself, the insects, in the number and the diversity of the objects which it includes, is equivalent to the entire plant kingdom. The class of polyps is probably much more numerous still. But we will never be able to congratulate ourselves that we know the total number of animals making up that class.

As a result of the extreme multiplication of small species, above all of the most imperfect, the quantity of individuals could injure the preservation of races and of the progress acquired by the improvement in organic structure, in a word, of the general order, if nature had not taken precautions to restrict this multiplication within limits which it can never cross.

Animals eat one another, except those which live on plants. But the latter run the risk of being eaten by carnivorous animals.

We know that the strongest and the best armed are the ones which eat the more feeble and that the large species devour the smaller ones. However, individuals of the same race rarely eat each other. They make war on other races.

The multiplication of the small animal species is so great and the renewal of their generations so quick that these small species would make the earth uninhabitable for others if nature had not placed a limit on their prodigious reproduction. But since they serve as prey for a multitude of other animals, since the length of their lives is very limited, and since cooler temperatures kill them off, their quantity is always maintained at just the right proportions for the preservation of their races and of the others.

As for the larger and stronger animals, they would be in a position to become dominant and to threaten the preservation of many other races if they were able to reproduce in very large numbers. But their races prey on each other and they reproduce only slowly and in small numbers at any one time. This fact once again preserves the equilibrium of the species at the right level.

Finally, man alone, considered apart from everything unique to him, seems able to reproduce indefinitely. For his intelligence and his methods protect him from seeing his numbers halted by the voracity of any of the animals. He exercises such a supremacy over them that instead of having to fear the largest and strongest animal races, he is able to destroy them, and every day he reduces their individual numbers.

But nature has given him numerous passions which, unfortunately, develop along with his intelligence, thus placing a large obstacle to the extreme multiplication of the individuals of his species.

In fact, it seems that man himself is charged with constantly reducing the number of those like himself. For I am not afraid to state that the earth will never be covered with the population which she can feed. Several of its habitable parts will always be alternately very lightly populated, although the time periods for these fluctuating alterations for us will be infinite.

Thus, by wise precautions, everything perpetuates itself in the established order. Changes and constant renewals seen in this order are held within limits which they cannot cross. The races of living bodies all remain despite their variations. The progress acquired in the improvement of organic structure has lost nothing. Everything which seems disorder, reversal, anomaly constantly returns to the general order and even contributes to it. And everywhere and always the will of the sublime Author of nature and of all that exists is invariably brought about.

Now, before busying ourselves with a demonstration of the degradation and the simplification which exist in the organic structures of animals, as we proceed from the most complex to the simplest, following common practice, let us examine the present state of their distribution and classification, as well as the principles which have been used to establish these. Then it will be easier to recognize the proofs for the degradation in question.


Notes to Chapter Four

(1) Hydrogéologie, p. 41 ff. [Back to Text]

(2) In another work (Hist. nat. Des Végétaux, éditon de Déterville, vol.I, p. 202) I have dealt with some other similar phenomena observed in plants, for example, in hedysarum girans, dionoea muscipula, the stamens of the flowers in berberis, and so on, and I have revealed that the odd movements which we see in the parts of certain plants, principally in hot weather, are never the result of real irritability, or really of any of their fibres; they are rather sometimes hygrometic or pyrometric effects, sometimes the results of elastic relaxation which takes place under certain circumstances, and sometimes caused by swelling and weakening of parts, by the more or less rapid local accumulation and dissipation of invisible elastic fluids which the plants must excrete. [Back to Text]


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