From Joshua S. Weitz and Steven W. Wilhelm at The Scientist (2013, but worth revisiting):
There are an estimated 1031 viruses on Earth. That is to say: there may be a hundred million times more viruses on Earth than there are stars in the universe. The majority of these viruses infect microbes, including bacteria, archaea, and microeukaryotes, all of which are vital players in the global fixation and cycling of key elements such as carbon, nitrogen, and phosphorus. These two facts combined—the sheer number of viruses and their intimate relationship with microbial life—suggest that viruses, too, play a critical role in the planet’s biosphere.
Of all the Earth’s biomes, the ocean has emerged as the source for major discoveries on the interaction of viruses with their microbial hosts. … Among these discoveries are “giant” marine viruses, with capsid cross-sections that can exceed 500 nm, an order of magnitude larger than prototypical viruses. Giant viruses infect eukaryotic hosts, including the protist Cafeteria and unicellular green algae.6,7 These viruses also carry genomes larger than nearly all previously identified viral types, in some cases upwards of 1 million base pairs. In both marine and nonmarine contexts, researchers have even identified viruses that can infect giant viruses, the so-called virophages,8 a modern biological example of Jonathan Swift’s 17th-century aphorism: “a flea/ Hath smaller fleas that on him prey;/ And these have smaller fleas to bite ’em;/ And so proceed ad infinitum.”More.
Understanding the role of viruses in the history of life has been handicapped by the debate as to whether viruses are alive. But that seems to be an issue around definition among terms associated with life. Apparently, 123 definitions are on offer.
Thought experiment: A teapot is not alive. How do we know it is not? It meets none of the criteria for being alive. No one would consider such a notion. But viruses meet some of the criteria for being alive.
Would an accurate understanding of viruses help us with the origin and evolution of life?
See also: Why “evolution” is changing? Consider viruses
What we know and don’t know about the origin of life
Hat tip: Suzan Mazur
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