. . . .The theory of the descent of the species is fully developed [in the Critique of Judgment], even including, as an explanation for the current fixity of the species, a theory of the former, now extinct, fertility of the productive force, such as Georges Cuvier was to advocate subsequently.
Nineteenth-century theories of evolution, especially Darwin's, added factual details to Kant's theory and improved it by removing many objective difficulties, but they changed nothing in the basic framework. On the other hand, compared to Kant's theory, the theories of the nineteenth century actually represent a huge step backward on account of the decline of theoretical culture and the consequent naiveté with which relatively insignificant details are considered important and lauded as progress in treating the question, while the crucial speculative-theoretical basic questions are overlooked.
Kant deals briefly but thoroughly with these crucial questions in a few sentences appended to the well-meaning consideration of the possibility of a real descent of species. He points out that if the radically immanent theory of evolution were accepted, researchers would have to ascribe to the universal mother, with her generative power, an expedient organization geared to all the creatures that have come forth from her and without which the appropriate forms of the animal and plant worlds would be impossible. "They have then only pushed the basis of explanation further back and cannot claim to have made the development of those two kingdoms independent of the prerequisite of ultimate causes." In this one sentence the idea of the inner law of evolution is carried to its conclusion—at the same time that its theoretical significance is blunted.
The turn to the theory of evolution has the theoretical goal to explain the building principle [Baugesetz] of each species based on the preceding evolution of species. If this idea is followed to its logical conclusion, the law according to which species develop moves closer and closer to the beginning of the history of evolution, until the first life-form is endowed with the evolutionary tendency for the entire living world, and finally speculation pushes back beyond the first life-form into inorganic matter, from which the former spontaneously originated. The "explanatory" law that was intended to be immanent thus turns again into a transcendent one, into a law that "precedes" the evolutionary series of life. And the types of organisms, the species, in spite of their supposed historical descent from each other, nevertheless stand again side by side, inexplicable through each other since the conditions for the development of any one species cannot be found in the one that precedes it historically and generationally, but only in the law that stands outside the whole series of species.
The attempt to "explain" the species leads to the unexpected result that the species once again stand side by side as fixed types, similar to the way Linnaeus saw them, even though in reality they may be related to one another through genesis.
We have come to the end of our investigation of the transformation of the idea of the transcendence of evolution to that of immanence. Just as for the organic individual his structural law, the immanence of his being, could not be replaced by the preformist theory of the series, just as there the problem of infinity had to be resolved within the species in order to arrive at the finite concept of the individual life-form's formative drive, so in the theory of evolution the doctrine of the descent of species must be dissolved as the explanation of the individual species, so that the idea of the fixity of the species, of the immanent law of the species form, can be found again.
The theoretical situation is only less transparent in evolutionary theory than in the infinite series of species. While in the latter we only had to trace the dissolution of the concept of series to arrive at the immanent concept of the organism, in evolutionary speculation we had to (1) investigate the transformation of evolutionary theory from the transcendent to the immanent idea, as it ran its course from Leibniz to Herder, Goethe, and Kant; and (2) see, behind the evolutionary theory's becoming immanent, the dissolution of its explanatory law all the way to the reappearance of the fixity of the species.
Kant's argument that the theory of evolution merely shifts the real origin of the species back to the origin of evolution not only takes the theory of evolution to its logical conclusion but also destroys it as meaningless as far as its explanatory purpose is concerned. It does not explain what it was intended to explain, in fact, it explains just as little as Leibniz' principle of continuity or Herder's or Goethe's idea of morphological kinship.
The kinship relationships of the living world are primary phenomena just as the life of the species and the life of the individual organism are primary phenomena, which one can see or not, but there is nothing about them that needs to be explained. The primary phenomenon of life becomes visible in a threefold way: in the living individual, in the species, and in the interconnectedness of the entire living world. It is impossible to use a part of this phenomenon to explain the same phenomenon in another of its manifestations.
The life of the individual cannot be explained through the life of the species, as the theory of series has attempted to do; the life of the species cannot be explained by the totality of the phenomenon of life, as the theory of evolution attempts to do; and the totality of the phenomenon of life can most definitely not be explained through the laws of non-living nature. In the substantially genuine movement of the spirit, the theory of evolution has come to an end in the Critique of Judgment although in the history of derivative theories on this issue, theories that move ever farther away from the center of the spirit, evolutionary theory did not flourish until the following century.
Kant appended a note to his radical destruction of the explanatory value of any theory of evolution in which he conceded that the fact of bodily kinship was not impossible. It was not, he remarked, totally absurd and a priori impossible that, for example, certain water animals might gradually evolve into marsh animals and, after some further generations, into land animals. "However, experience gives no example of it; according to experience, all generation that we know is generatio homonyma. This is not merely univoca in contrast to the generation out of unorganized material, but it brings forth a product that is in its very organization like the one that produced it; and generatio heteronyma, so far as our empirical knowledge of nature extends, is found nowhere." This sentence, written in 1790, still applies word for word today; biology has nothing to add to it.