The Distribution and Classification of Animals

Why do we need to distribute and classify animals?*

The distribution of animals is used to obtain:

• a convenient list to consult
• the very order of nature

This order is clearly characterized by the relationships Nature has established between the animals.

The classification of animals is to furnish, with the help of lines of separation traced in various places in the general series of creatures, points where our imagination can stop so that we can more easily recognize each race which has already been observed, grasp the interconnections with the other known animals, and place in each group the new species which we succeed in discovering.

This method compensates our weaknesses, makes our studies and our understanding easier, and its use is indispensably necessary to us.

But I have already shown that it is a product of art and that, despite any appearance to the contrary, it has no real connection with nature.

The proper determination of the interconnections between things will always establish in our general distributions:

1. The place of the large groups or the primary divisions
2. The groups subordinate to the first
3. The species or races which have been observed

The knowledge of the interrelationships is advantageous since these interrelationships are the work of nature itself.

No naturalist would ever have the power or, no doubt, the desire to change the results of a known interrelationship.

The general distribution thus will become more and more perfect and compelling to the extent that our understanding of the interconnections advances with respect to the things which make up a kingdom.

The case is different with classification or with the lines of separation used to trace from place to place in the general distribution, whether of animals or plants.

As long as there will be spaces to fill in our distributions, because many animals and plants have not yet been observed, we will always find with these lines of separation that they seem to us created by nature itself.

But this illusion will vanish to the extent that we continue to observe. And already have we not seen a sufficiently large number of them disappear, at least in the smallest groups, through the numerous discoveries of naturalists in roughly the last fifty years?

Thus, apart from the lines of separation which are the result of gaps which we have to fill, those which we will always be forced to create will be arbitrary and hence changeable, as long as naturalists do not adopt some conventional principle to regulate themselves when they draw such lines.

In the animal kingdom, we should consider as a conventional regulatory principle the fact that every class should be understood to consist of animals characterized by a particular structural system. The strict application of this principle is easy enough and presents only moderate inconveniences.

In fact, although nature does not move abruptly from one structural system to another, it is possible to establish some limits between each system, so that throughout nature there is only a small number of animals placed near these limits and in a position to raise some doubts about their true class.

The other lines of separation which sub-divide the classes are, in general, more difficult to fix, because they rest on less important characteristics and, for this reason, are more arbitrary.

Before examining the present state of the classification of animals, let me attempt to show that the distribution of living beings must form a series, at least with the large groups, and not a ramified network.

The classes must form a series in the distribution of animals

As human beings are condemned to go through all possible mistakes before recognizing one truth when they examine the facts which are relevant to it, people have denied that the productions of nature in each kingdom of living creatures were really in the position of being able to form a true series which follows a consideration of their interrelationships, and we have not wished to recognize any scale in the general arrangement, whether of animals or plants.

Thus, since naturalists have noticed that many species, certain genres, and even some families appear in a sort of isolation so far as their characteristics are concerned, several of them have imagined that the living creatures in one kingdom or the other, which according to their natural interconnections are closely related to or very distant from each other, are distributed like the different points of a geographical map or a globe. They consider the small and very pronounced series which have been called natural families as organized in the form of a network. This idea, which has appeared sublime to some moderns, is clearly a mistake. And it will undoubtedly disappear as soon as we have a more profound and more universal understanding of organic structure, above all when we distinguish what belongs to the influence of habitats and acquired habits from what is the result of more or less advanced progress in the composition or the perfecting of organic structures.

In the meantime, I am going to show that nature gives rise, with the help of a great deal of time, to the existence of all animals and plants and has really established in each of these kingdoms a true ladder with respect to the growing complexity in the organic structure of these living beings, but that this ladder, which it is our concern to recognize in dealing with these things according to their natural interrelationships, only offers comprehensible gradations in the main large groups of the universal series and not in species, nor even in the genres. The reason for this point stems from the fact that the extreme diversity of circumstances in which the different races of animals and plants find themselves is not related to the increasing complexity in the organic structure among them, as I will show, and that gives rise in their shapes and exterior characteristics to anomalies or types of leaps which the increasing complexity in the organic structure could not have brought about by itself.

It is therefore a matter of proving that the series which makes up the animal ladder consists essentially in the distribution of the principle groups which make it up and not in the distribution of species, nor even in that of the genera.

The series which I am going to talk about could not therefore be established except in the placing of the large groups, because these groups which make up the classes and the large families each consist of beings in which the organic structure depends upon some particular system of essential organs.

Thus each distinct large group has its own particular system of essential organs. And it is these particular systems which are going to deteriorate from the one which shows the greatest complexity right to the one which is the simplest. But each organ considered in isolation does not follow such a regular path in its deterioration. To the extent that the organ has less importance and is more susceptible to being modified by circumstances, it follows such a path even less.

In fact, the organs with little importance or inessential to life are not always similar to each other in their perfection or degradation, so that if we follow all the species of a single class, we will see that a particular organ in a particular species enjoys the highest degree of perfection, while some other organ which, in this same species, is much impoverished or very imperfect, is found very perfected in some other species.

These irregular variations in the perfection and the degradation of non-essential organs come up in those organs more subject than others to the influence of external circumstances. This influence brings with it similar variations in the shape and in the nature of the most external parts and gives rise to such a large and strangely organized diversity among species, that instead of being able to arrange them, like the large groups, in a unique series, simple and linear, in the form of a regularly graduated scale, these same species often form around the large groups of which they are a part, lateral branches, whose extremities display truly isolated points.

To modify each interior system of organic structure requires a more influential combination of circumstances and a much longer period of time than to modify and change the external organs.

Nevertheless, I notice that when circumstance demand, nature goes from one system to another, without making a jump, provided that the systems are closely related. In fact, it is by this faculty that nature has managed to form all systems successively, going from the most simple to the most complex.

It is so true that nature has this faculty, that it moves from one system to another, not only in two different families when they are related by their interconnections, but even in a single individual.

The system of organic structure which include as organs of respiration real lungs are more closely related to systems which include gills than those which require tracheae. Thus, not only does nature move from gills to lungs in the neighboring classes and families, as a consideration of fish and reptiles shows, but it moves there even during the life of individuals themselves, who enjoy successively both systems. We know that frogs, in the imperfect tadpole state, breathe by gills; whereas, in their more perfect condition as frogs they breathe by lungs. We do not see anywhere nature passing from a system of tracheae to a pulmonary system.

Thus, it is true to say that there exists for each kingdom of living beings a unique and graduated series in the arrangement of the large groups, in conformity with the increasingly complexity in the organic structure and with the arrangement of things according to a consideration of the interrelationships and that this series, whether in the animal or plant kingdom, must offer at its front extremity the simplest and the least organized living creatures and finish with the most perfect in structure and faculties.

Such appears to be the true order of nature, and such is effectively what the most attentive observation and a sustained study of all the features which characterize its progress clearly present to us.

Since the time when, in our distributions of the production of nature, we have felt it necessary to concern ourselves with the interrelationships, we are no longer masters at arranging the universal series as we please. The knowledge which we increasingly acquire of nature’s progress, to the extent that we study the close or distant interrelationships which it has established, whether between objects or between their different groups, carries us along with it and forces us to conform to nature’s order.

The first result obtained from the use of interrelationships in the placement of the large groups to form a general distributions is that the two extreme ends in the order must display the most dissimilar beings, because they are effectively the most distant so far as such interrelationships are concerned and, as a result, so far as organic structure is concerned. It follows from this that if one of the extremities of the order shows living beings developed in the most perfect way, those in which the organic structure is the most complex, the other extremity of the same order must necessarily show the most imperfect living creatures, that is to say, those in which the organic structure is the simplest.

In the general disposition of the known plants, according to the natural method, that is to say, according to the consideration of the interrelationships, as yet we understand reliably only one of the extremities of the order: we know that the cryptogram must be located at this extremity. If the other extremity is not established with the same certainty, that stems from the fact that our knowledge of the organic structure of plants is much less advanced than what we understand about a large number of known animals. Consequently, so far as plants are concerned, we do not yet have a certain guide to determine the interrelationships between the large groups, of the sort that we have for recognizing those which exist between the genera and which form the families.

We do not encounter the same difficulty with the animals. The two extremities of their general series are determined in a definite way. For as long as we attach importance to the natural method and, as a result, to the consideration of the interrelationships, the mammals will necessarily occupy one of the extremities of the order, whereas, the infusorians will be placed at the other extremity.

Therefore, there is for animals, as well as for plants, an order which belongs to nature and which, like the things which this order brings into existence, results from the methods which nature has received from the Supreme Author of all things. It is nothing other than the universal immutable order which this Sublime Author has created in everything, together with the collection of general and particular laws to which this order is subject. By these means, which nature continues to use, it has given and perpetually is giving life to its productions. It varies them and renews them without ceasing, and in this way maintains the entire order which comes from these means.

We are going to see that this natural order which we were concerned successfully to recognize in each kingdom of living beings and of which we already possess various sections in the well known families and in our best genera, is, so far as the animal kingdom is concerned, now determined in its entirely in a manner which leaves no room for anything arbitrary.

But the large number of the various animals which we have succeeded in understanding and the numerous insights which comparative anatomy has provided about their organic structure now give us the means of determining, in a definitive manner, the general distribution of all the known animals and of assigning a confirmed rank for the main divisions which we can establish in the series which they form.

That is what it is important to recognize and what will be truly difficult to dispute.

Let us now move on to an examination of the present state of the general distribution of animals and of their classification.