Goethe, in his 1796 Third Lecture on Anatomy, presents his first outline of metamorphology, comparing human affinities and bonds to chemical affinities and bonds, therein presaging evolution theory and the first draft notes of his Elective Affinities (1809), which initiated the science of human chemistry (see: Goethe timeline).

“To facilitate our comprehension of the concept of organic existence, let us first take a look at mineral [inorganic] structures. Minerals, whose varied components are so solid and unchanging, do not seem to hold to any limits or order when then combine, although laws do determine these conditions. Different components can be easily separated and recombined into new combinations. These combinations can again be taken apart, and the mineral we thought destroyed can soon be restored to its original perfection.

The main characteristic of minerals that concerns us here is the indifference their components show toward the form of their combination, that is, their coordination or subordination. There are, by nature, stronger or weaker bonds between these components, and when they evidence themselves, they resemble attractions between human beings. This is why chemists speak of elective affinities, even though the forces that move mineral components [or humans] one way or another and create mineral structures are often purely external in origin, which by no means implies that we deny them the delicate portion of nature’s vital inspiration that is their due.

How different even imperfect organic beings are! They convert part of the nourishment they absorb—eliminating what they do not need—into distinct organs. What they do absorb they turn into something unique and exquisite by joining most intimately one element with another and so forming differentiated parts in whose forms multifarious life is manifested. And if these forms are destroyed, they cannot be reconstructed from what remains.

If we compare these imperfect organic beings with higher ones, we find that the former, even though they make use of elemental influences with a certain degree of force and individuality, cannot bring the resulting organic parts to the same level of specialization and permanence as the higher animal forms can. We know, for example, that plans—and we will not descend any lower on the scale of organic life—developing as they do in a certain sequence, represent one and the same basic organ in highly different shapes.

Detailed insight into the law governing this metamorphosis will surely advance the science of botany, not only in its descriptive tasks but also in its efforts to understand the inner nature of plants.”

“Goethe’s first detailed presentation of ‘affinity’ occurs in his third Lecture on Anatomy of 1796 (LA, I, 9, pgs. 202f). Brief though this treatment is, it reveals how thoroughly Goethe had absorbed the current theory, and how radically he was beginning to transform it. Interestingly, Goethe steers a path between the existing views by granting that ‘affinities’ operate ‘according to fixed laws’, whilst denying that they have a definable ‘limit’. Thus he accepted the general theory, yet rejected the possibility of establishing a fixed ‘order’ that could be summarized in a table.”

— Jeremy Adler (1990), “Goethe's use of chemical theory in his Elective Affinities” [2]