One nature (branching law)
Romanian-born American mechanical engineer Adrian Bejan's 2012 depiction of how the geometry of flow structures found surrounding river deltas and lung bronchi are both governed by one law of nature, which Bejan calls "constructal law". [4]
In science, one nature, as contrasted with two natures, refers to the conviction or view that one nature governs the entire universe, animate and inanimate, governing both humans and human activities, and other non-human things, alike.

Belief systems of people, generally, can be divided into whether one is a two nature theorist or one nature theorist or two nature in belief and philosophy or one nature in belief and philosopher.

Goethe
In circa 1770, German polyintellect Johann Goethe, the preeminent "one nature theorist", as he states in his retrospect book 20 of his Poetry and Truth (1811-1814), how, in his pre-1775 youth years, he was searching for a universal rule to explain the happenings of existence, which he recounts as follows: [1]

“I perceived something in nature (whether living or lifeless, animate or inanimate) that manifested itself only in contradictions and therefore could not be expressed in any concept, much less any word. It was not divine, for it seemed irrational; not human, for it had no intelligence; not diabolical, for it was beneficent; and not angelic, for it often betrayed malice. It was like chance, for it laced continuity, and like providence, for it suggested context. Everything that limits us seemed penetrable by it, and it appeared to dispose at will over the elements necessary to our existence, to contract time and expand space. It seemed only to accept the impossible and scornfully to reject the possible.”

Later, following the completion of his tripartite chemical-to-animal-to-human tripartite metamorphology theory of form change, in his famous 4 Sep 1809 anonymous advertisement, shown below, to his soon-to-be published “most dangerous work” Elective Affinities, Goethe states explicitly there is after all only one nature:

“The author must have been led to his strange title by his continuing work in the physical sciences where we often make use of comparisons drawn from the world of human behavior so that things which are essentially remote from us may be brought a little nearer; and in the novel, in a case concerning morality, doubtless the author was seeking to trace an expression used as an analogy in chemistry back to its origin in the life of the human spirit. [The advertisement concludes with a general remark, the essence of which is] there is after all only one nature, and that even in our human zone of it, the cheerful zone of reason and freedom of choice, still there are traces, in the passions, of bleak and irresistible necessity.”

Haken
In 1986, German theoretical physicist Hermann Haken, in his Advanced Synergetics, gave the following noted one nature statement: [3]

“Why should systems consisting of components as different as electrons, atoms, molecules, photons, cells, animals, or even humans be governed by the same principles when they organize themselves to form electrical oscillations, patterns in fluids, chemical waves, laser beams, organs, animal societies, or social groups.”

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Bejan
In 1995, Romanian-born American mechanical engineer and thermodynamicist Adrian Bejan, after being irked by a prebanquet speech by Belgian chemist Ilya Prigogine about how natural structures are all but the result of throwing the dice, or as Bejan recalls: [4]

“Echoing the scientific community’s conventional wisdom, this famous man asserted that three-shaped structures that abound in nature—including river basins and deltas, the air passages in our lungs, and lightning bolts—were aléatoires (the result of throwing the dice). That is, there is nothing underlying their similar design. It’s just a cosmic coincidence.”

A statement which Bejan discredits with the following comparison of the flow shape structure of the Delta of the Lena River, Siberia and the Bronchus of a human lung, both shown adjacent, which he argues are governed by the same "constructal law" of nature. In his 2012 book Design in Nature, Bejan summarizes his one nature philosophy as such:

“Design in nature as a scientific discipline, [is] centered on a physics law of design and evolution: the constructal law. This law sweeps the entire mosaic of nature from inanimate rivers to animate designs, such as vascular tissues, locomotion, and social organization.”

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See also
‚óŹ Forest blind

References
1. Schwartz, Peter J. (2010). After Jena: Goethe’s Elective Affinities and the End of the Old Regime (pg. 19). Publisher. Bucknell University Press.
2. Goethe, Johann. (1994). Elective Affinities (introduction, note on translation, selected bibliography, chronology, and explanatory notes by David Constantine). World Classics.
3. Haken, Herman. (1983). Advanced Synergetics (Amz) (quote, pgs. xii-viii). Springer.
4. Bejan, Adrian and Zane, J. Peder. (2012). Design in Nature: How the Constructal Law Governs Evolution in Biology, Physics, Technology, and Social Organization (pgs. 1-2). Doubleday.

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