====== The origins of viruses ======

The evolutionary origins of viruses is disputed. Although they don't leave a fossil record it's known that they are ancient (at around 4.5 billion years old).

It's not known, however, whether they evolved //from// cellular lifeforms, or //pre-dated// them.

>There are three classical hypotheses on the origins of viruses: • Viruses may have once been small cells that parasitised larger cells (the degeneracy hypothesis, or reduction hypothesis); 
>• Some viruses may have evolved from bits of DNA or RNA that "escaped" from the genes of a larger organism (the vagrancy hypothesis, or escape hypothesis);
>• Viruses could have evolved from complex molecules of protein and nucleic acid before cells first appeared on earth (the virus-first hypothesis). None of these hypotheses have ever been fully accepted." \\ 
>Source : [[https://en.wikipedia.org/wiki/Viral_evolution#Origins|Wikipedia]]

//Note//: Another theory is that viruses may have evolved away from Earth, arriving here from deep space. The //Panspermia// theory - the roots of which go back at least as far as the 5th century BCE - was popularized in the 1980s by Fred ([[content/physics/cosmology/big_bang|'big bang']]) Hoyle and Chandra Wickramasingh. Although there is now a growing body of evidence appearing to support the theory - or at least not contradict it - it's still not widely accepted by experts in the field.

Further reading [[https://www.sciencedirect.com/science/article/abs/pii/S0065266020300249|Advances in Genetics, Volume 106, pp.101-107]]

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