From these beginnings, Ray's Methodus Plantarum penetrates the problem most deeply. The concept of the total habitus had been attained, and this phenotypical habitus, whose traits can be summarized as a type, was now understood as the expression of a life unity, a vital essence.
Outwardly, the way it is defined still follows the traditional logical forms: "Definitio perfecta conficitur e Genere proximo et Differentia essentiali" [A perfect definition consists of a proximate genus and an essential difference]—but the differentia specifica has been replaced by the differentia essentialis. The species-distinguishing trait was traditionally understood as a trait of the phenotype pure and simple, but the essential characteristic is for Ray the manifestation of an essence behind the appearance. "At essentiae rerum nobis incognitae sunt, proinde et Differentiae earum essentiales." [But the essences of things are unknown to us, inasmuch as their essential differences are.]
The real-ontological concept of essence is introduced to contrast on the linguistic level the real natural life unity with the concept, weighed down by logic, of the species, and the expression differentia essentialis has the function of relating the individual trait to the life form in which it appears, while the differentia specifica points to the position of the concept in the logical system of classification.
Thus, the contrast between the descriptive-classifying concept formation (the scholastic system, in Kant's language) and the research guided by the natural divisions (Kant's natural system) appears even on the level of terminology. In fact, it has been claimed that Ray also formulated the criterion of a natural division: the interfertility of supposed individuals to belong to the same subdivision.
If this is true, then Ray's theory would have already contained all the ideas that served Kant as the basis for his uncommonly drastic statements on the essence of the life form. And these statements by Kant, in turn, pursue the possibilities inherent in these fundamental ideas to the point that current biological theory, insofar as it deals with them at all, has nothing really new to add.
Kant distinguishes between the scholastic classification of phenomena and the other type of classification that is based on the natural divisions. The interfertility of individuals determines whether they belong to the same natural division, a principle ascribed to Ray and for which Kant draws on Buffon. Scholastic classification concentrates on classes according to similarity, while natural classification arranges phyla according to kinship: "the former intends merely to subsume creatures under headings, but the second wants to place them under laws."
The designation of natural subdivisions is thus simplified significantly compared to the Linnaean system; the distinction between genera and species disappears, and the term phylum designates the individuals who belong together according to the above-mentioned criterion; all larger groupings are artificial. The variations within the phyla are divided into races —hereditary varieties—and variations—differences that are not necessarily hereditary.
This was the precursor of the modern system of species, mutations, and variations, though it was not yet as clearly defined because the facts of genetics were not yet known. The individual natural divisions, the phyla, are constant, as were the Linnaean species, and the races developed within the phyla through the unfolding of dispositions that were present in seminal form in the as yet undifferentiated phyla.
The potential of developing in one or another direction was already present, but it was realized only when particular external conditions occurred, which then favored the unfolding of one potential while allowing others to wither. This explains why the races we find today can no longer regress to their undifferentiated phyla or develop in completely different directions.
There is obviously a close kinship between this theory and Heinz Woltereck's most recent studies—in both, a natural division, the species, is considered the smallest, so far at least, biological division, and both theories interpret hereditary mutations or races as unfoldings of what was already inherent in the nature of the phylum. To use Woltereck's formulation, the viable hereditary traits are already predetermined through the reaction norm of the species; mutations beyond the boundaries of the species' constitution are not possible.
Kant is exemplary in his further application of this principle of interpretation to the variations down to the individual level, a part of the theory completely lacking in modern race theories—not because of the subject matter, but only because of the authors' deficient theoretical background.
Even in the personal variations nature does not proceed in complete freedom, but according to Kant, just as in the case of race characteristics, nature develops the original predispositions of the phylum. "The variety among people of the very same race was, in all probability, as effectively inherent in the original phylum in order to establish and subsequently develop the greatest diversity for an infinite variety of purposes, as the difference between races was present to later develop into fitness for fewer but more essential purposes."
Race is not the ultimate determinant of the individual phenotype; rather every one of its traits must be regarded as the direct unfolding of the predispositions of the human phylum. The possibilities of human nature are spread out before us in the infinite variety of individual forms. That individual characteristics are not heritable Kant takes as an indication that nature "does not want the old forms always replicated but instead desires the expression of all the variety it had embedded in the original germs of the human phylum."
In the field of biology (there is nothing similar in anthropology) it is once again Woltereck who comes closest to this view. For him the variations are also determined by the reaction norm.
Kant, however, goes further and (more important for anthropology than biology) develops the idea of the bodily singularity of each person, so that only the human species as a whole can express the human essence in bodily form through all its individuals throughout history. Kant cites the physiognomical uniqueness and inner unity of every human face, thus transferring the problem of singularity from the merely physical sphere into that of spiritual expression. The idea of the singular body-mind unified person is almost attained here, though not yet completely. . . .