Non-cellular life
Non-cellular life is life that exists without a cellular structure. This term presumes the phylogenetic scientific classification of viruses as lifeforms, which is a controversial issue.
Hypothesized artificial life may or may not be considered living. (See definition of life.)
Some biologists refer to wholly syncytial organisms as "acellular" because their bodies contain multiple nuclei which are not separated by cell membranes, however these cell-bound organisms are outside the scope of the present article.
History
For about 100 years, the scientific community has struggled to understand what viruses are. First seen as poisons, then as life forms, then biological chemicals, and today many scientists think of viruses as existing at the border between chemistry and life: a gray area between living and nonliving.
It is not clear if all small viruses have originated from more complex viruses by means of genome size reduction. A viral domain of life may only be relevant to certain large viruses such as nucleocytoplasmic large DNA viruses like the Mimivirus. A 2012 study on viruses' protein folding and structure, suggests that the giant viruses, such as Mimivirus, are a separate domain of life, alongside the traditional three of Eukarya, Prokarya and Archaea. The study suggests that giant viruses have evolved from more complex organisms into their highly parasitic form, and are an ancient lineage, alongside that of the other three domains.
