From Citizendium, the Citizens' Compendium
A living system:
- Has to be separated from its environment.
- Has to perform metabolism with its environment.
- It must replicate itself.
- It has to have a polymer type subsystem carrying information.
- It must have an autocatalytic system, which is connected to the metabolism and creates the stuff needed to grow its boundary and to replicate its information system.
Such a system may be called alive, since it can live, replicate in its proper environment and it can evolve, since there is an information system.
T. Gánti: The principles of life Oxford University Press 2003.