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My question is out of curiosity and got me thinking. How did viruses with the head, tail and tail fibres actually evolve? These viruses look more like machines than biological entities. Are there any theories to how these viruses evolved?

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Does a biological entity not look like a machine? Look closer. – Preece Apr 17 '12 at 0:52
A bird looks like an aeroplane too... – nico Apr 19 '12 at 18:50
If you look from another perspective machines resemble biological entities. – kiran Jul 5 at 11:07
up vote 13 down vote accepted

I found a book chapter for you here

Quick summary: 3 hypotheses to Origin of viruses

  1. From pre-cellular world (virus first hypothesis)
  2. From reductive evolution of parasites (reduction hypothesis)
  3. From fragments of cellular genetic material (escape hypothesis)


  1. virus require cells (to infect) so how can they come first
  2. virus do not look like known reduced parasites from Bacteria/Eukarya/Archaea
  3. unlikely that genetic fragments form complex viral structures for viral function

Because of these drawbacks, the problem of virus origin was for a long time considered untractable and not worth serious consideration

The rest of the chapter looks more in-depth into the 3 hypotheses

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Could you summarise in your answer perhaps? It’s preferred here to preferred here to provide links for further information and references, not as the sole point of the answer. – Konrad Rudolph Apr 19 '12 at 9:47

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