Abstract
Viruses, including the SARS-CoV-2 virus responsible for the current COVID-19 epidemic, are a key to the understanding of life and evolution. Cells may have arisen from aqueous sequestration inside a lipid envelope studded with chromophores capable of capturing solar photons. Nitrogen incorporation in the primordial cell chemistry allowed synthesis of amino acids and nucleic acids, a prelude to RNA and subsequently DNA. Metagenomics provides access to nucleoprotein sediments synthesised by a googol of metabolically differentiated cells that have marked the evolution of life. Replication of a virus, a nucleoprotein particle, occurs passively in competent cells. Viruses are only identified in the context of the epidemic that they induce as a result of transmission from one host to another. By breaking down the viral particle, the host cell appears to resurrect the metabolic function of the nucleic acid, which synthesises its components without any form of control. Viral products undergo self-assembly and are exported by either exocytosis or cytolysis. In the absence of cells, viruses appear to be inert. However, intracellular contamination of a virus does not always result in replication: the viral genome can disappear, remain latent, wake up, remain embedded in the cellular genome, become an oncogene or induce auto-immunity. The presence of endogenous retroviruses in eukaryotic cells raises the question of their possible role in evolution.