Life by Assembly Line1: A Century-Long Quest to Build Life—And Define It

Synthetic biology increasingly pursues the construction of engineered biological systems, yet the field lacks operational categories for interpreting claims of “life creation”. Rather than asking whether life has already been created in the laboratory, this article argues that synthetic biology requires a pragmatic framework that distinguishes modification, reconstruction, assembly, and autonomous synthesis of biological systems. Building on a historical analysis of recurring life-creation claims throughout twentieth-century biology, we develop a taxonomy that situates contemporary synthetic biology and xenobiology along a continuum of increasing engineering depth. Current achievements—including genome rewriting, orthogonal translation systems, and expanded genetic codes—represent a deep reconstruction of living systems, but do not yet constitute fully autonomous synthetic life. To clarify these distinctions, we introduce several conceptual tools: the Pasteurian Wall separating living from non-living systems, the Genetic Firewall as a biosafety principle for engineered organisms, and an Expanded Chemoton framework that provides an engineering-oriented operational definition of life based on metabolic autonomy, informational closure, and evolvability. Together, these elements allow experimental systems to be positioned along a functional continuum from sophisticated biochemical artifacts to genuinely alternative living systems. By replacing metaphor-driven narratives with operational categories, this framework aims to strengthen conceptual clarity, experimental comparability, and governance of emerging synthetic life technologies.