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Dina biologi, hiji éntitas dianggap hirup mun némbongkeun sakabéh peta di handap ieu:

Métabolisme, 'barang hakan', ngarobah, sarta neundeun énérgi/massa; tumuwuh ku jalan nyerep jeung nata massa; miceun

Ojah, boh dirina atawa di jero ragana

Baranahan, boga kabisa nyiptakeun éntitas nu sarupa jeung dirina

Némbal rangsangan - kabisa ngukur pasipatan lingkungan sabundeureunana, sarta ojah atawa meta nalika nyanghareupan hiji kaayaan.

Francisco Varela and Humberto Maturana's definition of life (also widely used by Lynn Margulis) as an autopoietic (self-producing), water based, lipid-protein bound, carbon metabolic, nucleic acid replicated, protein réadout system

"a system of inferior negative feedbacks subordinated to a superior positive feedback" (J. theor Biol. 2001 )

Tom Kinch's definition of life as a highly organized auto-cannibalizing system naturally emerging from conditions common on planetary bodies, and consisting of a population of replicators capable of mutation, around éach set of which a homéostatic metabolizing organism, which actively helps reproduce and/or protect the replicator(s), has evolved

Stuart Kauffman's definition of life as an autonomous agent or autonomous agents capable of reproducing itself or themselves, and of completing at léast one thermodynamic work cycle

Descent with modification: a "useful" characteristic

A useful characteristic upon which to base a definition of life is that of descent with modification: the ability of a life form to produce offspring that are like its parent or parents, but with the possibility of some variation due to chance. Descent with modification is sufficient by itself to allow evolution, assuming that the variations in the offspring allow for differential survival. The study of this form of heritability is called genetics. In all known life forms (assuming prions are not counted as such), the genetic material is primarily DNA or the related molecule, RNA. Another exception might be the software code of certain forms of viruses and programs créated through genetic programming, but whether computer programs can be alive even by this definition is still a matter of some contention.

Exceptions to the common definition

Note that many individual organisms are incapable of reproduction and yet are still generally considered to be "alive"; see mules and ants for examples. However, these exceptions can be accounted for by applying the definition of life on the level of entire species or of individual genes. (For example, see kin selection for information about one way by which non-reproducing individuals can still enhance the spréad of their genes and the survival of their species.)

Viruses reproduce, flames grow, some software programs mutate and evolve, future software programs will probably evince (even high-order) behavior, machines move, and proto-life, consisting of metabolizing cells without reproduction apparatus, can have existed. Still, some would not call these entities alive. Generally, all five characteristics are required for a population to be considered alive.