S if for Symbiosis

Symbiosis refers to an interdependency between two different species.  We see examples of symbiosis all the time, though we may not always recognize them for what they are.  Our own digestive tracts are filled with bacteria.  The bacteria have a warm, nutrient-filled environment in which to thrive, and they help us process the foods that we eat.

The following video does a great job of explaining the different types of symbiotic relationships in greater detail.

We see plenty of examples of symbiotic relationships in science fiction.  In the Star Trek universe, we see the Trill, a species that can play host to a symbiont.  Not all Trill are paired with a symbiont, but those who are gain the memories of the new creature inhabiting their body.  The person playing host is permanently altered by the experience, and the symbiont is able to have a many new experiences they wouldn’t have been able to enjoy before.  The joining undeniably changes them both, but what kind of symbiotic relationship do they have?  It’s certainly beneficial for the symbiont, but could it be beneficial for the Trill as well?  Trill society, after all, reveres the idea of being a host, perhaps because it has been a fact of life for so long that it’s become an integral part of the culture.  Not all Trill can be hosts, so perhaps this too makes it seem like being chosen is an honor rather than an obligation.  How would you feel about having another intelligent organism living inside your body, knowing that you would never be the same as you were beforehand?

We also have the terrifying scenario in Alien, where the xenomorphs reproduce using the bodies of other creatures to reproduce.  The process is nonconsensual, and the births are violent, resulting in a gruesome death for the host.  We are treated as little more than incubators, our humanity denied.  Does this make the xenomorphs monstrous?  Or, since it is crucial to their survival, should we look at it merely as a creature acting according to its instincts?

There are also plenty of examples of science fiction where we see alien intelligences taking over a creature altogether.  These body-snatching scenarios seem far more sinister than mutually beneficial symbiotic relationships, in that there seems to be no semblance of the original person left.  For beings that value the freedom to make decisions and to act of our own volition above all else, this is a horrifying prospect.  Why are body-snatching and mind control scenarios so prevalent in science fiction?  What real world fears do these stories touch upon that make them so scary for audiences?

What other symbiotic relationships can you think of?  Which kind of symbiotic relationship do you find the most disturbing, and why?