previrus

A previrus is a theoretical intermediate stage in the origin of life, specifically in the development of viruses. The concept proposes that viruses did not originate as independent entities but rather evolved from components of cells that escaped or were released. In this model, genetic material, possibly DNA or RNA, along with some basic protein components, would have become encapsulated within a lipid membrane derived from a host cell. This encapsulated entity would then exist in a state prior to the full development of a replicative cycle, relying heavily on host cell machinery for any form of propagation.

The previrus hypothesis suggests that such entities would have gradually acquired the ability to infect other cells, initially through simple mechanisms like diffusion or fusion. Over evolutionary time, these previruses would have developed more sophisticated ways to hijack host cell processes, leading to the genomes and replication strategies observed in modern viruses. This perspective contrasts with theories that posit viruses arose from free-living organisms that subsequently became parasitic, or that they are remnants of pre-cellular life. The previrus concept places the origin of viruses firmly within the context of cellular life's evolution.