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Gerard Jagers op Akkerhuis, Sr. Scientist, Wageningen U. and Research Ctr, Wageningen, Netherlands

Jagers op Akkerhuis, Gerard. 2009. Towards a Hierarchical Definition of Life, the Organism, and Death. Foundations of Science, no. Special Issue of the Conference on the Evolution and Development of the Universe (EDU-2008). In press.

To some, a virus, a cell and a robot are life. Others consider only cellular beings life. Despite hundreds of definitions, there is no consensus about a system-based definition. This is problematic for the practical and theoretical progress in various disciplines, including exobiology, artificial life, biology and evolution. This paper suggests a way to improve upon this situation. In an earlier paper, I have introduced the ‘operator hierarchy’, offering a strict complexity ranking of systems, from superstrings to animals with brains. Here I use this hierarchy for defining life, the organism and death, and explore the application of these definitions in practical situations.

The operator hierarchy allows defining life as ‘matter with the configuration of an operator, and that possesses an equal, or an even higher complexity than the cellular operator’. Living, then, is synonymous to the dynamics of such systems. I suggest considering as organisms only operators fitting the present definition of life. In this context, its existence as an operator represents the minimum condition defining an organism, construction being more essential than metabolism, growth or reproduction. In the operator hierarchy, closures define complexity levels, for example from pro- to eukaryote and from uni- to multicellular. These closures, allow defining death as ‘the loss of an organism’s typical closure in the course of an irreversible process of deterioration’. The generality of the operator hierarchy also offers a context for discussing ‘life as we do not know it’. The paper ends with a range of practical examples, including viruses, mitochondria, robots, flowers in a vase, prions, etc.