Metaphysical man is dead; our whole field of enquiry is transformed by physiological man.

The line encapsulates Zola’s naturalist polemic: modern inquiry, he argues, should abandon abstract, speculative accounts of “man” (metaphysics, moral essences, a priori psychology) in favor of an empirically grounded understanding rooted in the body—heredity, nerves, environment, and measurable causes. “Physiological man” signals the 19th‑century turn toward medicine and experimental science as models for studying human behavior. In Zola’s program, the novelist becomes a kind of investigator, tracing how physical constitution and social conditions shape desire, vice, and fate. The claim is also rhetorical: it declares a break with earlier literary idealism and legitimizes a new, scientifically inflected realism.