The Definition of Life

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.

Publication Status Statement: This article is a preprint of the "Life Theory" series research, intended to facilitate early academic exchange and feedback. Its final revised version is planned for formal publication in the future. This version is released under the CC BY-NC-ND 4.0 license.