View of Haeckel

Ernst Haeckel viewed the World Riddle as a dual-question of the form, "What is the nature of the physical universe and what is the nature of human thinking?" which he explained would have a single answer since humans and the universe were contained within one system, a mono-system, as Haeckel wrote in 1895:
"KELVIN SMITH LIBRARY" (about Haeckel book on Monism),
Case Western Reserve University, Cleveland, Ohio, 2004, webpage: CaseEdu-HaeMon00:
notes Monism book as dated 1895.
"7mono10 txt" (description of Ernst Haeckel's book
Monism as Connecting Religion and Science),
Project Gutenberg Literary Archive Foundation, webpage: GutenbergOrg-7mono10:
book "translated from German by J. Gilchrist, M.A., B.Sc., PH.D."].
[From Monism as Connecting Religion and Science by Ernst Haeckel (translated):]

"The following lecture on Monism is an informal address delivered extemporaneously on October 9, 1892, at Altenburg, on the seventy-fifth anniversary of the "Naturforschende Gesellschaft des Osterlandes." ... The "exacting" Berlin physiologist shut this knowledge out from his mind, and, with a short-sightedness almost inconceivable, placed this special neurological question alongside of the one great "world-riddle," the fundamental question of substance, the general question of the connection between matter and energy. As I long ago pointed out, these two great questions are not two separate "world-riddles." The neurological problem of consciousness is only a special case of the all-comprehending cosmological problem, the question of substance. "If we understood the nature of matter and energy, we should also understand how the substance underlying them can under certain conditions feel, desire, and think." Consciousness, like feeling and willing, among the higher animals is a mechanical work of the ganglion-cells, and as such must be carried back to chemical and physical events in the plasma of these. -Ernst Haeckel, 1895

Haeckel had written that human behavior and feeling could be explained, within the laws of the physical universe, as "mechanical work of the ganglion-cells" as stated.