The Definition of Life

Abstract This article is part of the author's "Treatise on Life Series," which aims to construct a unified theoretical framework extending from the definition of life to the emergence of complex systems. Traditional definitions of life have predominantly focused on enumerating specific attributes such as metabolism, cellular structure, or autopoiesis. These approaches often encounter significant difficulties when confronted with borderline cases like cryptobiotic organisms and viruses, even fostering a sense of "definitional pessimism." This paper argues that the root cause lies in attempting to define life by listing "state attributes," thereby overlooking its essence as realized through its core functions. We propose that life can be precisely defined as: a physical system capable of utilizing environmental resources to produce copies of itself (hereditary capacity), wherein the copying process can accommodate and transmit limited hereditary variation. This definition establishes "hereditary capacity" and "limited hereditary variation" as the core criteria for life, shifting the focus from "what life is" to "what life does and what its core functions necessarily entail." It not only provides clear and consistent explanations for borderline cases while effectively excluding non-living replication phenomena, but also offers a universal theoretical foundation for research into artificial life and extraterrestrial life. About The Treatise on Life SeriesThe Chinese title 生论 (Shēng Lùn) carries a profound philosophical connotation that exceeds the English word "life." The character 生 (shēng) signifies not merely the state of being alive, but the dynamic, ceaseless process of coming-into-being, generation, and perpetual transformation—a concept resonant with the ancient Chinese wisdom of "生生不息" (shēng shēng bù xī), the endless cycle of birth and rebirth. This series explores life not as a static entity but as an ongoing process of becoming.