Zoological Philosophy
J. B. Lamarck

[This translation, which has been prepared by Ian Johnston of Malaspina University-College, Nanaimo, BC, Canada, 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 Two

The Importance of Considering Affinities

Among living bodies, the term affinity (between two things being examined comparatively) has been given to analogous or similar traits, taken from the totality or the general features of their parts, but with more value attached to the most essential parts. The more extensive and similar these traits, the more significant the affinities between the objects which display them. They indicate some sort of family connection among the living things under consideration and make one aware of the need to bring them together in our distributions in a manner proportional to the significance of their affinities.

What a change the natural sciences have undergone in their progressive march since people started to pay serious attention to a consideration of these affinities, and above all since we determined the true principles concerning these affinities and their value!

Before this change, our botanical distributions were entirely ruled by the arbitrary and competitive artificial systems of all authors; and in the animal kingdom, the invertebrates, which include the largest part of known animals, showed in their distribution the most disparate collections, some under the name insects and others under the name worms, including animals which, from any consideration of their affinities, are the most different and the most widely separated from each other.

Fortunately, matters have now changed in this respect. And from now on, if we continue to study natural history, its progress is guaranteed.

Consideration of the natural affinities prevents all arbitrariness on our part in the attempts we make to arrange organic things methodically. It demonstrates the natural law which must guide us in the natural method. It forces the views of naturalists to agree about the rank which they assign at first to the principal groups which make up their arrangements, and later about the particular objects which make up these groups. Finally, such a consideration constrains them to reproduce the very order which nature has followed in giving life to her productions.

Thus, everything concerning the affinities existing among the different animals must constitute, before any division or classification of them, the most important object of our research.

In this discussion here of a consideration of the affinities, it is not a matter only of those which exist between the species; it is at the same time a question of determining the general affinities of all the orders close to or far away from the groups which one must compare.

Although the interrelationships are very different in value depending on the importance of the parts which establish them, they can nevertheless extend to include the shape of the external parts. If they are so significant that, not only the essential parts but even the exterior parts present no discernible difference, then the objects under scrutiny must be individuals of the same species. But if, in spite of the extent of their affinities, the exterior parts display perceptible differences which, however, are always less significant than the essential similarities, then the objects under scrutiny must be considered different species of the same genus.

The important study of affinities is not limited to comparing classes, families, and even species amongst themselves in order to determine the interrelationships which exist among these objects. It includes also a consideration of the parts which make up the individuals. In comparing among them the same sorts of parts, this study discovers a reliable means to recognize either the identity of individuals of a common race or the difference between distinct races.

In fact, it has been noted that the proportions and the arrangements of the parts of all the individuals making up a species or a race always appear the same and thus appear to remain constant. Hence. it has reasonably been concluded that, after an examination of a few isolated parts of an individual, it is possible to determine to what species, familiar or new to us, these parts belong.

This method is very conducive to the advancement of our knowledge about natural productions at the time which we are observing. But what we determine from this method can be valid only for a limited time period. For with respect to the condition of their parts, the races themselves change to the extent that the circumstances influencing them undergo significant transformation. True, since these transformations occur only extremely slowly, at a rate which makes them always imperceptible to us, the proportions and arrangements of the parts always appear the same to the observer, who in practice never sees them change. And when he comes across some which have undergone these changes, since he has not been able to observe them, he assumes that the perceptible differences have always existed.

It is nevertheless true than in comparing the same type of parts belonging to different individuals, it is easy to determine reliably the close or distant affinities which exist between these parts and, consequently, to recognize if these parts belong to individuals of the same or of different races.

It is only the general conclusion which is faulty, having been drawn too rashly. I will have more occasion to establish this point in the course of this work.

The affinities are always incomplete when they deal only with a solitary analysis, that is to say, when they are determined only after an analysis of one part taken by itself. But however incomplete, these affinities based on the inspection of a single part have nevertheless an importance directly proportional to the essential nature of the part under scrutiny, and vice versa.

Thus, there are determinable degrees among the known affinities and important values among the parts capable of establishing these interrelationships. To be sure, this knowledge would have remained without practical use if, in living creatures, we had not distinguished the most important parts from those of less importance, and if, among these important parts, which are of several types, we had not found the principle appropriate to establishing among them non-arbitrary values.

The most important parts which must establish the principal affinities in the animals are those essential to the preservation of their life and in the plants those essential to their reproduction.

Thus, in the animals, we will always determine the main interrelationships according to the interior organic structures. In the plants we will always seek out in the parts which produce the fruit the affinities which can hold between different living things.

But since, with animals and plants, the most important parts for analysis in the search for affinities are of different types, the only principle which it is convenient to use to determine in a non-arbitrary manner the degree of importance of each of these parts consists in considering either the most important use which nature makes of it or the special importance of the faculty resulting from that part in animals which possess it.

In the animals, where the internal organic structure provides the major affinities for analysis, three sorts of special organs are, with good reason, selected out from the others as the most relevant for establishing the most important interrelationships. The following list indicates them in order of their importance.

1. The organ of feeling. The nerves, since they have a central connection, whether unique (as in the animals with a brain) or multiple (as in those which have a longitudinal marrow with ganglia)

2. The organ of respiration. The lungs, gills and the tracheae;

3. The organ of circulation. The arteries and the veins, most commonly with an active central point, the heart.

The first two of these organs are more frequently employed in nature, and thus are more important than the third, that is, the organ of circulation. For the latter disappears after the crustaceans; whereas, the first two still extend to the animals in the two classes which follow the crustaceans.

Finally, of the first two, the organ of feeling must have more value for establishing affinities, for it produces the most eminent of the animal faculties. Moreover, without this organ muscular action would not take place.

If I was going to talk about plants, in which the parts essential for reproduction are the only ones which provide the main characteristics for determining their affinities, I would present these parts in their order of value or importance as follows:

1. The embryo, its accessories (the cotyledons, the perisperm), and the seed which contains it;

2. The sexual parts of flowers, such as the pistil and the stamens;

3. What surrounds the sexual parts; the corolla, the calyx, and so on;

4. The seed casing, or the pericarp;

5. The reproductive bodies which do not need any pollination.

These principles, for the most part recognized, give a consistency and a reliability to the natural sciences which they did not have previously. The affinities which have been determined by conforming to such principles are not at all subject to variations of opinion. Our general distributions are becoming secure, and to the extent which we perfect them with the help of these methods, they will get closer and closer to the very order of nature.

After having sensed the importance of the analysis of affinities, in fact, we saw the birth of those attempts made (above all in the last few years) to establish what is being called the natural method, something which is only the sketch traced by man of the route nature follows to brings its productions into existence.

Nowadays in France it is no longer a question of those artificial systems based upon characteristics which jeopardize the natural affinities between the objects subjected to such systems, ones which establish division and distributions detrimental to the advancement of our knowledge about nature.

So far as animals are concerned, we are now convinced, for good reasons, that we can determine the natural affinities only through their organic structures. Consequently, zoology will derive all the insights necessary for the determination of these affinities from comparative anatomy. But it is important to note that it is the particular facts which we must assemble from the works of the anatomists who have set out to discover them, and not always the conclusions which they have drawn from these facts. For too often, these conclusions encourage opinions which could lead us astray and prevent us from grasping nature's laws and her true design. It appears that each time someone observes any new fact whatsoever, he is condemned to hurl himself into error through his desire to assign a cause to it; his imagination is so fecund in the production of ideas, because he neglects too much the need to guide his judgments by the totality of the collection which observations and the other assembled facts can present to him.

When we work on natural affinities between objects and judge these interrelationships well, bringing together the species according to this analytical principle and assembling them in groups within certain limits, the groups make up what are called genera. Similarly the genera, organized according to an analysis of the affinities and combined also into groups larger than theirs, form what are called families. When these families are combined in the same way under the same analytical principle, they form the orders. The latter by the same process first separate out the classes. Finally, these groups divide up each kingdom into its principal sections.

Therefore, the well-determined natural affinities must guide us in forming our collections, when we establish the divisions of each kingdom into classes, each class into orders, and each order into sections or families, each family into genera, and each genus into different species, as required.

We are perfectly justified in thinking that the total series of beings making up part of a kingdom, once that series is distributed in an order subject throughout to the analytical principle of affinities, represents the very order of nature. However, as I showed in the preceding chapter, it is important to bear in mind that the different types of divisions which we must establish in this series so that we can know the objects in it more readily are not part of nature at all and are truly artificial, although they display portions of the same order which nature has set up.

If we add to these considerations the points that in the animal kingdom the affinities must be determined mainly according to organic structures and that the principles which we must use to establish these affinities must not leave the least doubt about what they are based on, we will have, in all these matters, solid foundations for zoological philosophy.

We know that all science must have its philosophy and that by this route science makes real progress. It is futile for naturalists to waste their time in describing new species, seizing upon all the slight modifications and the small particularities of their variations to augment the immense list of species drawn up in a list, in a word, setting up genera in various ways and constantly changing the analytical principles used to characterize them. If science neglects philosophy, its progress will not be real, and the entire work will remain imperfect.

It is really only since we set about establishing the close or distant interrelationships existing among the various natural productions and among the objects comprising the different groups we have created among these productions that the natural sciences have acquired some reliability in their principles and a philosophy which turns them into real sciences.

How much our arrangements and our classifications would improve each day from the sustained study of the affinities among objects.

In fact, by studying these affinities I recognized that the infusorian animals could no longer be grouped with the polyps in the same class, that the radiates must no longer be confused with the polyps, and that the soft ones, like the medusas and other neighbouring genera which Linnaeus and even Bruguière placed among the mollusks, are essentially like the echinoderms and should form a special class with them.

Again, by studying affinities I became convinced that the worms form an isolated group, including animals very different from those which make up the radiates and (for stronger reasons) the polyps, that the arachnids could no longer be a part of the class of insects, and that the cirrhipedes were neither annelids nor mollusks.

Finally, by studying affinities I managed to make a number of essential improvements to the arrangement of mollusks, and I recognized that the pteropods, although distinct, because of their affinities are very nearly related to the gasteropods and must be placed between the acephalic mollusks, to whom they are close, and the gasteropods. These pteropods have no eyes, like all the acephalids, and almost always lack a head; even the Hyalae have only the appearance of one. See the specific distribution of Mollusks in Chapter Seven, which ends this first part.

As for plants, when the study of the affinities among the different recognized families has given us more insight and we better understand the rank which each of them must occupy in the general series, then the distribution of these living bodies will leave nothing to be determined arbitrarily and will conform more to the very order of nature.

This, the importance of the study of affinities among the objects we observe is so evident that we must nowadays look upon this study as the most important of those which can advance the natural sciences.


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