3 ms·

I guess the layman's followup question (if I may) is, why didn't something like Smallpox spread over to the Americas, if viruses are that prevalent? Why did the

I guess the layman's followup question (if I may) is, why didn't something like Smallpox spread over to the Americas, if viruses are that prevalent? Why did they need a human host? Is there a specific evolutionary niche to not being infectious via the air?

ridgeguy 9y ago
It might be that airborne transport imposes barriers that smallpox didn't evolve to meet. Perhaps something like resistance to degradation by UV in sunlight. If so, maybe the apparently large cohort of viruses that do survive airborne dispersal is only a small fraction of the actual virus inventory on our planet.
amelius 9y ago
IANAB, but perhaps the concentration is too low to cause any harm?
knappa 9y ago
I would think that the virii that have that kind of prevalence are mostly bacteriophages.
- keithwhor 9y ago
  This is the correct answer. Viruses are also very specialized molecular machinery, and eukaryotic cells (and by extension, organisms) are quite complex. Think of molecular evolution between viruses v. prokaryotes / eukaryotes like a constant arms race: viruses have the "key" to (1) enter a cell and (2) hijack cellular machinery, and prokaryotes / eukaryotes are constantly upgrading their locks (mostly as a factor of diversity x natural selection --- the cells without great locks tend to be terminated rather quickly). Also consider that it's not in a virus' "best interest" (from a sustainability / propagative standpoint) to actually kill or even incapacitate 100% of their hosts, which contradicts their very mode of replication (often completely hijacking transcription and translation mechanisms in a cell, leading to lysis). They rely on these hosts to survive --- a 100% termination rate of the host means an evolutionary dead-end for a virus. Arguably, the most "successful" viruses are ones that have been incorporated into host DNA - it's estimated that up to 8% of our genome consists of endogenous retrovirus DNA [1]. After all, viruses are simply small containers of self-replicative material (DNA / RNA, a few proteins) surrounded by a protein coat: if they can hijack their own environmental shield (like, say, a full human nucleus / cell) and still propagate their DNA they've arguably "won." So --- yeah, harmful virulence is (1) tough to achieve and (2) not actually all that evolutionarily advantageous. [1] https://en.wikipedia.org/wiki/Endogenous_retrovirus https://en.wikipedia.org/wiki/Endogenous_retrovirus
  - sitkack 9y ago
    How much genetic complexity exists just to thwart viruses?

ridgeguy 9y ago

It might be that airborne transport imposes barriers that smallpox didn't evolve to meet. Perhaps something like resistance to degradation by UV in sunlight. If so, maybe the apparently large cohort of viruses that do survive airborne dispersal is only a small fraction of the actual virus inventory on our planet.

amelius 9y ago

IANAB, but perhaps the concentration is too low to cause any harm?

knappa 9y ago

I would think that the virii that have that kind of prevalence are mostly bacteriophages.

keithwhor 9y ago
This is the correct answer. Viruses are also very specialized molecular machinery, and eukaryotic cells (and by extension, organisms) are quite complex. Think of molecular evolution between viruses v. prokaryotes / eukaryotes like a constant arms race: viruses have the "key" to (1) enter a cell and (2) hijack cellular machinery, and prokaryotes / eukaryotes are constantly upgrading their locks (mostly as a factor of diversity x natural selection --- the cells without great locks tend to be terminated rather quickly). Also consider that it's not in a virus' "best interest" (from a sustainability / propagative standpoint) to actually kill or even incapacitate 100% of their hosts, which contradicts their very mode of replication (often completely hijacking transcription and translation mechanisms in a cell, leading to lysis). They rely on these hosts to survive --- a 100% termination rate of the host means an evolutionary dead-end for a virus. Arguably, the most "successful" viruses are ones that have been incorporated into host DNA - it's estimated that up to 8% of our genome consists of endogenous retrovirus DNA [1]. After all, viruses are simply small containers of self-replicative material (DNA / RNA, a few proteins) surrounded by a protein coat: if they can hijack their own environmental shield (like, say, a full human nucleus / cell) and still propagate their DNA they've arguably "won." So --- yeah, harmful virulence is (1) tough to achieve and (2) not actually all that evolutionarily advantageous. [1] https://en.wikipedia.org/wiki/Endogenous_retrovirus https://en.wikipedia.org/wiki/Endogenous_retrovirus
- sitkack 9y ago
  How much genetic complexity exists just to thwart viruses?