The Sethis are natives of the world Set-3, one of the planets that humanity has colonized. Prior to the arrival of of humanity on the planet, while the Mimic Fungus was the dominant lifeform on the planet it was not yet sentient. That changed when the first spores mimicked human brain chemistry, gaining sentience for themselves. They are highly evolved, highly adaptable sentient fauna that has mimicked humanity down to almost every detail. There are a few changes, however, like the lack of sweat ducts and the lack of a blinking reflex, relics of an imperfect copying process.
They have no culture of their own that predates humanity, so they have adapted the culture of the Terran Federation wholesale. At this point, they consider themselves less a different, alien species from humanity than they do a different race of humans that happened to originate from off Earth.
Set-3 Mimic Fungus Lifecycle:
The Set-3 Mimic Fungus releases two types of spores – mimic, and reproduction. Mimic spores spread out until they encounter an organism that isn’t a variant of the Mimic Fungus, and it would enter the body and infect it but it wouldn’t seek to destroy the cells. Instead, it would leech energy from the system to support replicating itself as it studied the structure of complex organs and tissue as it slowly spread through the entire host body, learning how it was put together. Once it had mapped the structure of the host body, the Mimic Fungus begins giving off reproduction spores through whatever excretion systems it used (for humans, it used sweat mostly), laying thousands of seeds with instructions on how to grow a copy of the host organism.
The original parasite would remain, living in its host, until the host eventually died or the immune system fought it off… in the case of the humans, it was eventually removed by a combination of medicine and surgery, and vaccinations were developed to prevent future infections. The spores that it shed, however, grew up into new organisms… variations on the original infected host, which in this case of mimicking humanity became the sentient Sethis.
These Sethis also were infectious, giving off mimic spores that sought to infect their own targets and copy them as well, but as it turns out the Sethis have much better conscious control of this system than we do of many of our own automated processes – they can’t stop spores from trying to infect things once released, but they can stop their body from producing any of the infectious things.
Sethis don’t have quite the same emotional brain chemistry as humans. It makes them slightly less prone to feeling the extremes of human emotion, and better at focusing. This, over time, has been stereotyped into making them almost robotic in their emotionlessness… this is not true.
Swampies. Shrooms. Kelpies.