What Is the Essence of Living Matter

Oparin (1938) proposed that living matter be defined as having the following properties: metabolism, self-reproduction, and mutability. Eigen (1971) observed that these criteria could be met by decidedly non-biological entities such as von Neumann's "self-reproducing automata," or various robots. Even some simple biological systems are somewhat ambiguous regarding their "life-like" status. Primitive systems which blur the distinction between animate and inanimate include viruses, prions (protein crystals which may be causative agents in some human diseases) and proteinoids (self organizing protein assemblies) implicated in life's origins (Fox, 1972). Independent cytoskeletal elements also have characteristics of being "alive." The slithering microtubules which R. D. Allen and colleagues (1985) isolated from squid axoplasm ambulate, avoid collisions, and have a sense of direction. Are they alive? If future technologies lead to nanoscale replicating automata, the distinction between living and nonliving entities will be further clouded.

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