|An example of phototropism, a type of tropism, defined as growth or a turn towards light or a source of photons, e.g. sunlight.|
In 1888, Jacques Loeb, in his “The Orientation of Animals to Light”, introduced his tropism theory or forced movement theory of action (see also: induced movement), the beginning of a long effort to overthrow that anthropomorphic-view of animal and plant movement, e.g. that protoplasmic substances move toward the source of light, "because of curiosity", as many argued during Loeb's day. 
In 1918, Loeb, in his Forced Movements, Tropisms, and Animal Conduct, stated, in effect, that Galilean-based tropism usurps Aristotelian-based teleology, as the explanative model in biology (chnopsology):
“The Aristotelian viewpoint still prevails to some extent in biology, namely that an animal moves only for a purpose, either to seek food or to seek its mate or to undertake something else connected with preservation of the individual or the race. The Aristotelians had explained the process in the inanimate world in the same teleological way. Science began when Galileo overthrew this Aristotelian mode of thought and introduced the method of quantitative experiments which leads to mathematical laws free form the metaphysical conception of purpose. The analysis of animal conduct only becomes scientific in so far as it drops the question of purpose and reduces the reactions of animals to quantitative laws.”
|A 2010 view (Ѻ) of the tropism of human molecules, according to Russian physical chemist Georgi Gladyshev, which he believes is but one of many type of tropism, governed by his theory of hierarchical thermodynamics.|
Humans | Psychological chemotropism
In 1898 to 1903, Ernst Haeckel, in his love letters, mentions the concept of elective affinity at least three times in respect to his own romantic relationships, and in one letter to a Franziska von Altenhausen, defined, his own elective affinity to her as a strange psychological chemotropism: 
“… seductive women—why should I, despite all scruples and obstacles, cast myself into the dust before you? Dearst Franziska, herein lies the enigma of ‘elective affinity’, of that strange psychological ‘chemotropism’, of whose power I have spoken repeatedly in my books—little dreaming that I myself should fall a victim to it in my old age!”
In other words, the way a person orients their reaction existence (life) towards, around, or in the direction of a loved one, or the person to whom the elective affinities direct them is similar to the way a plant turns toward or grows to sunlight, according to Haeckel.
The following are related quotes:
“The tropism of human molecules is governed by human and hierarchic thermodynamics which explain tropism via Gibbs' equilibrium criteria.”— Georgi Gladyshev (2010), crowd photo (Ѻ) description statement, Jun 8
“All types of tropisms in the universe can be explained using hierarchical thermodynamics.”— Georgi Gladyshev (2010), plant photo (Ѻ) description statement, Jun 12
● Retinal molecule | ABC model
1. Loeb, Jacques. (1888). “The Orientation of Animals to Light” (“Die Orientierung der Tiere gegen das Licht”), Sitzngsb. Wurzb. Physik.-md. Ges. Publisher.
2. Haeckel, Ernst. (1930). The Love Letters of Ernst Haeckel: Written Between 1898 and 1903 (editor: Johannes Werner) (elective affinity, pgs. 101, 212, 260). Methuen.
● Tropism – Wikipedia.