Living systems

Some scientists have proposed in the last few decades that a general theory of living systems is required to explain the nature of life.

[11] The idea that Earth is alive is found in philosophy and religion, but the first scientific discussion of it was by the Scottish geologist James Hutton.

[12]: 10  The Gaia hypothesis, proposed in the 1960s by James Lovelock, suggests that life on Earth functions as a single organism that defines and maintains environmental conditions necessary for its survival.

[17] Robert Rosen devoted a large part of his career, from 1958[18] onwards, to developing a comprehensive theory of life as a self-organizing complex system, "closed to efficient causation".

This was formulated by first considering how macroscopic order is generated in a simple non-biological system far from thermodynamic equilibrium, and then extending consideration to short, replicating RNA molecules.

[24][25] Gerard Jagers' operator theory proposes that life is a general term for the presence of the typical closures found in organisms; the typical closures are a membrane and an autocatalytic set in the cell[26] and that an organism is any system with an organisation that complies with an operator type that is at least as complex as the cell.

[33] Budisa, Kubyshkin and Schmidt defined cellular life as an organizational unit resting on four pillars/cornerstones: (i) energy, (ii) metabolism, (iii) information and (iv) form.

Cells as self-sustaining units are parts of different populations that are involved in the unidirectional and irreversible open-ended process known as evolution.