Thread:BainTheCool/@comment-30615939-20171209175257/@comment-30615939-20171211172923

Non-cellular life is life that exists without a cellular structure for at least part of its life cycle.[1] Historically, most (descriptive) definitions of life postulated that a living organism must be composed of one or more cells,[2] but this is no longer considered necessary, and modern criteria allow for forms of life based on other structural arrangements.[3] [4] [5] [3]

The primary candidates for non-cellular life are viruses. A minority of biologists consider viruses to be living organisms, but most do not. Their primary objection is that no known viruses are capable of autopoiesis, which means they cannot reproduce themselves: they must rely on cells to copy them.[1] [6] [7] [8] [9] However, the recent discovery of giant viruses that possess genes for part of the required translation machinery has raised the prospect that they may have had extinct ancestors that could evolve and replicate independently. Most biologists agree that such an ancestor would be a bona fide non-cellular lifeform, but its existence and characteristics are still uncertain.[1] [10] [11] [12] [13]

Engineers sometimes use the term "artificial life" to refer to software and robots inspired by biological processes, but these do not satisfy any biological definition of life.