Where do viruses come from?

If viruses live to replicate, where did they come from in the first place?

• How did viruses first come into existence. To me it seems so strange, not only the way it looks, but it's function as well. Were they created on Earth where they have come to evolve, or originate from space?

• Answer:

  Although the answer to your question remains speculative, there seems to be a strong evolutionary relationship between viral genomes and the genomes of everything else. That is, viruses likely co-evolved along with living organisms and did so, as you point out, because it was easy for them to harness the cellular pathways of host organisms for their own replication. The oft-repeated comparison between a biological virus and a software virus is apt. Both use existing infrastructures to replicate themselves. See: http://www.nature.com/scitable/topicpage/the-origins-of-viruses-14398218 If you are suggesting that a virus has a rather senseless, or perhaps sinister existence because all it does is replicate, then you've expressed a somewhat anthropocentric view. In the broadest sense, all of biology serves the purpose of replication above and beyond any other function. The very definition of a successful organism is matter of population. At the moment Argentine ants, herpesviruses and humans are doing nicely whereas elephants, blue fin tuna and Tasmanian devils are on the wane. As for the contribution from space (i.e. the rest of the universe), all organisms and viruses owe their existence to the creation of chemical elements by fusion within stars. So far, nothing more complex than molecules such as polycyclic aromatic hydrocarbons and polyformaldehyde have been discovered in space. The space-capsule appearance of phage virus is less likely to be a product of alien origin than it is just another case of form following function. See: http://en.wikipedia.org/wiki/Cosmic_dust and http://en.wikipedia.org/wiki/Bacteriophage