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wintersdark t1_irn7ciu wrote

Reply to comment by uber_snotling in What lifeform has the shortest genetic sequence? by teafuck

Just following his line of thought, the key difference is that viruses don't replicate. Viruses force other cellular machinery to replicate them. Parasites do replicate on their own, it's just that often they do that within other organisms but as you said - environmental requirements are normal for all life.

If viruses bred or replicated on their own within cells I'd agree, but that is not the case.

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uber_snotling t1_irn8jgr wrote

What about the Cordyceps fungus that infects insects and grows out of their heads? Or wasps that lay eggs in caterpillars or tarantulas to reproduce?

Replication requires conducive environmental conditions that may require other life forms. Life evolves to replicate within an environment - viruses are no different.

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wintersdark t1_irnw9fw wrote

No, there's a fundamental difference here. I wouldn't disagree if viruses could reproduce but only inside certain cells - would would be no different than parasites as you say.

That isn't what happens.

When cordyceps infects an ant, it controls the ant, and grows out of its head. Birds eat it, and it's spores end up in the bird's poop. Edit for more detail: cordyceps literally eats the ant's tissue, and uses that biomass to grow and produce the spores that will end up in the bird's poop.

The fungus requires the bird for its life cycle, but the fungus grows and produces spores on its own.

So what happens with viruses is that they cause the cell itself to produce more viruses. Viruses don't reproduce on their own at all regardless of environment.

This is specifically what makes viruses so weird and prompts questions about whether they are even alive, because they are the only organism that doesn't reproduce. They don't lay eggs, have babies, mate, reproduce asexually, eat, or even have a life cycle so to speak.

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the_red_scimitar t1_irnyrgv wrote

Yeah, but when it comes to not replicating, and needing another life form to do so.. sounds like an analog for sexual reproduction. Virus needs some of the mechanisms in another cell in order to produce. A human needs some of the mechanisms in the opposite sex in order to reproduce.

Sexual reproduction as such, it is not a requirement for life, it's just one of the most common ways life works here.

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wintersdark t1_irojqsf wrote

Sounds like maybe but isn't.

Two members of a species being required for reproduction is still reproduction done within a species. The new human is grown of the mother, with the input of the same species male's genetic code to ensure diversity. It's not like the human male slaps the females bottom, which causes her to suddenly start continuously producing human males over and over again until she dies.

Many creatures reproduce by simply dividing too, but in that case as well the new creature is literally made of the parent creature. They reproduce.

If you're looking at what's actually happening and not a stand-off analogy, the end result is:

  • Viruses do not eat
  • Viruses do not reproduce. Target cells do not just provide the environment for reproduction(we don't care about environments), they actually do the reproduction, not just host it. The new viruses are literally made entirely of and by the host creature's cells. Viruses neither seed, spore, divide, bud, lay eggs, or birth babies.
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