The Importance of Considering Affinities

Among living bodies, ‘affinity’ is the similarity of traits of the the most essential parts of 2 things being compared.

The more extensive and similar these traits, the more significant the affinities between the objects.

They indicate some family connection among the living things.

The consideration of these affinities has changed the natural sciences!

Before this, our botanical distributions were ruled by the arbitrary systems of authors.

In the animal kingdom, invertebrates include the largest part of known animals.

These include insects and worms which are very different from each other.

Consideration of the natural affinities:

• prevents all arbitrariness in our attempts to arrange organic things methodically.
• demonstrates the natural law which guides us in the natural method.
• forces the views of naturalists to agree about the rank which they assign:
  • at first to the principal groups which make up their arrangements
  • later about the particular objects which make up these groups.
• constrains naturalists to reproduce the very order which nature has followed

Thus, the affinities among the different animals is the most important object of our research.

These affinities:

• are not only the currently existing ones between the species.
• include the general affinities of all the orders close to or far away from the groups which one must compare.

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 both the essential and exterior parts show no difference, then the objects under scrutiny are individuals of the same species.

But if, in spite of the extent of their affinities, the exterior parts have differences which are less significant than the essential similarities, then the objects are of a different species of the same genus.

The study of affinities is not limited to comparing classes, families, and species amongst themselves to determine interrelationships.

• 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.

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, 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.

But what we determine from this method can be valid only for a limited time period.

This is because the races themselves change extremely slowly.

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.

• Solitary analysis is analysis of one part taken by itself.
• Yet such incomplete affinities have direct importance proportional to the essential nature of that part, and vice versa.

Thus, there are:

• determinable degrees among the known affinities
• important values among the parts that can establish these interrelationships

This knowledge would be useless if:

• we had not distinguished the most important parts from those of less importance,
• 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 establish the principal affinities:

• in animals are those essential to the preservation of their life
• in plants those essential to their reproduction

Thus:

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

The most important parts of animals and plants for searching for affinities are of different types.

The only convenient principle for determining the importance of these parts is in considering either:

• the most important use which nature makes or
• the special importance of the faculty resulting from that part in animals which have it

In animals, the internal organic structure provides the major affinities for analysis.

3 sorts of special organs are the most relevant for establishing the most important interrelationships.

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 are more frequently employed in nature.

• Thus, they are more important than the organ of circulation which disappears in crustaceans

Whereas, the first 2 still extend to animals in the 2 classes which follow crustaceans.

The organ of feeling has more value for establishing affinities.

• It produces the most eminent of the animal faculties.

Without this organ, muscular action would not take place.