Life preys upon life. This is biology's most fundamental fact.

Fischer’s aphorism compresses an ecological and evolutionary observation into a stark moral-neutral statement: living systems persist by drawing energy and materials from other living systems. “Preys” can be read broadly—predation, parasitism, herbivory, microbial consumption, and even cellular processes that depend on organic matter produced by other organisms. By calling it biology’s “most fundamental fact,” the line emphasizes trophic dependence and the inevitability of competition and consumption in nature, pushing back against sentimental views of life as inherently harmonious. The phrasing also invites reflection on how scientific description can sound ethically charged (“preys”) even when intended as a value-free account of how life is sustained.