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> If you look at human history, contacts between peoples with different immune system resiliencies proved quite deadly. Between human species on Earth. Humans

> If you look at human history, contacts between peoples with different immune system resiliencies proved quite deadly. Between human species on Earth. Humans in the Americas were not genetically distinct from their European cousins, thus a European virus could readily infect an American human and vice versa (Europeans were not wiped out because the diseases they acquired were not as deadly, such as syphilis). Our immune systems are adaptive, but a bacteria/virus will be limited in it's ability to adapt. As such, it's pretty unlikely to be able to infect a complex, multicellular organism that it's never encountered before. The most likely vector for an attack is an alien bacteria that is able to rapidly transpose genetic code with earth-evolved bacteria and create a novel hybrid. Then you are dealing with a COV-19 type scenario.

ericmay 6y ago
Yes my point want that such a meeting would be similar, but that such a meeting between alien ecosystems could have a similar effect. To the larger point about the OP, my issue is the idea that any of this is unlikely, when there is a sufficient lack of information to base any sort of probabilistic assumption. They’re all simply incorrect because there is insufficient data. For all we know an alien organism may be specifically evolved to devour multicellular life, or pass into other organisms without detection. There is no reason to think the Ridley Scott scenario is any more or less likely than a harmless scenario. We just don’t know because our frame of reference is only life on Earth.
- arrosenberg 6y ago
  Sure, I get you. There are all kinds of possibilities in a vast universe. If, for the sake of discussion, we can assume that alien bacteria and viruses have roughly the same physical constraints — it's pretty unlikely you see that kind of adaptive behavior toward multicellular organisms. There is a physical limit on the size of bacterial genomes and viral RNA is a single set of instructions that get inserted into the host's own genome, so they literally can't be that complex. Every bacteria and virus on Earth targets a specific host, environment and/or life cycle - they have to specialize and adapt to survive. That's not to say we couldn't inadvertently pick up a bioengineered complex organism from an advanced alien species - that would be a completely different story.

ericmay 6y ago

Yes my point want that such a meeting would be similar, but that such a meeting between alien ecosystems could have a similar effect. To the larger point about the OP, my issue is the idea that any of this is unlikely, when there is a sufficient lack of information to base any sort of probabilistic assumption. They’re all simply incorrect because there is insufficient data. For all we know an alien organism may be specifically evolved to devour multicellular life, or pass into other organisms without detection. There is no reason to think the Ridley Scott scenario is any more or less likely than a harmless scenario. We just don’t know because our frame of reference is only life on Earth.

arrosenberg 6y ago
Sure, I get you. There are all kinds of possibilities in a vast universe. If, for the sake of discussion, we can assume that alien bacteria and viruses have roughly the same physical constraints — it's pretty unlikely you see that kind of adaptive behavior toward multicellular organisms. There is a physical limit on the size of bacterial genomes and viral RNA is a single set of instructions that get inserted into the host's own genome, so they literally can't be that complex. Every bacteria and virus on Earth targets a specific host, environment and/or life cycle - they have to specialize and adapt to survive. That's not to say we couldn't inadvertently pick up a bioengineered complex organism from an advanced alien species - that would be a completely different story.