Farmer & Belin’s Criteria of Life
- Life is a pattern in spacetime, rather than a material object. For example, most of our cells are replaced many times during our lifetime. It is the pattern and set of relationships that are important, rather than the specific identity of the atoms.
- Self-reproduction, if not in the organism itself, at least in some related organism. (Mules are alive, butcannot reproduce. Viruses can only reproduce with the aid of a host.)
- Information storage of a self-representation. For example, contemporary natural organisms store a description of themselves in DNA molecules, which is interpreted in the context of the protein/RNA machinery.
- A metabolism which converts matter and energy from the environment into the pattern and activities of the organism. Note that some organisms, such as viruses, do not have a metabolism of their own, but make use of the metabolisms of other organisms.
- Functional interactions with the environment. A living organism can respond to or anticipate changes in its environment. Organisms create and control their own local (internal) environments.
- Interdependence of parts. The components of living systems depend on one another to preserve the identity of the organism. One manifestation of this is the ability to die. If we break a rock in two, we are left with two smaller rocks; if we break an organism in two, we often kill it.
- Stability under perturbations and insensitivity to small changes, allowing the organism to preserve its form and continue to function in a noisy environment, or after being subjected to minor damage.
- The ability to evolve. This is not a property of an individual organism, but rather of its lineage. Indeed, the existence of a lineage is an important feature of living systems.
