In science, Hippolyte Adolphe Taine (1828-1893) was a French historian who coined the term "human molecule" in December of 1869 in the preface to his two volume book On Intelligence. [1]

In the preface he states ‘it is now admitted that the laws which rule formation, nutrition, locomotion, for bird or reptile, are but one example and application of more general laws which rule the formation, nutrition, locomotion, of every animal.’ He continues ‘in the same way we begin to admit that the laws which rule the development of religious conceptions, literary creations, scientific discoveries, in a nation, are only an application and example of laws that rule this same development at every moment and with all men.’ In other terms, Taine states, ‘the historian studies psychology in its application, and the psychologist studies history in its general forms.’ On this logic, Taine reasons:

"He first notes and follows the general transformations presented by a certain human molecule, or a certain peculiar group of human molecules; and, to explain these transformations, he writes the psychology of the molecule or its group."

In sum to the preface of his book, he states that ‘for the last fifteen years I have contributed to these special psychologies’. Moreover, ‘I now attempt a general psychology.’ He notes, however, that ‘to embrace this subject completely, this theory of the Intelligence (faculty of knowing) needs a theory of the will added to it.’

References
1. (a) Taine, Hippolyte. (1870). De l’Intelligence (On Intelligence), (Part I, Part II), (pg. xi-xii), London: L. Reeve and Co.
(b) Sparks, Jared. (1873). The North American Review, (Section: Taine’s philosophy, pg. 403: keyword: “human molecule”, pg). Vol. CXVII. Boson: James R. Osgood and Co.
(c) Thims, Libb. (2008). The Human Molecule, (preview). Morrisville, NC: LuLu.