Learning from Water: Two Complementary Definitions of the Concept of Life

The concept of life is central to biology and related life sciences, but there is no convergence on a definition. With the aim to resolve this problem analogies were studied between definitions of water and life. The concept of water refers to two phenomena: material particles (the H2O molecules) and interacting water molecules (liquid water). Likewise, the concept of life can be viewed as referring to a property of special material particles (the organisms) and to the system of interacting organisms (the ecosystem). In a comparable way as chemical theory has solved the problem of defining the water molecule, one can apply the Operator Theory for solving the problem of defining the organism concept. The analogy with water subsequently offers inspiration for two ontologically distinct definitions of life: (1) a definition of life as a general indication for a property that all organisms have, and (2) a definition of life that refers to a system of interacting organisms. These two definitions refer to different ontological kinds and accordingly cannot be merged into a single definition. For this reason the concept of life can be viewed as involving two, complementary, definitions. It is discussed how findings based on the water-life analogy contribute to current discussions about the definition of life.