Demi-Humans

[smirky]

I've been meaning to ask this for a while.

Demi-humans. Separate species or humans who have been genemodded (underwent gene-replacement therapy to gain their ears/tails/other qualities OR the offspring of genemodded ppeople)?

This is the big question. Everyone who played TiTS, aka Trials in Tainted Space (those who didn't, should) knows what genemods are. I've always leaned towards this solution because it's a lot less snowflake (where are all those other species apart from a few of their representatives), makes sense from a realistic point of view (technology is advanced, and even today, many people would undergo such a procedure) and literally offers a simple answer to the question which kind of makes sense from an in-universe point of view.

This could... also apply to literally all species that aren't standard ones. But that's another question itself.

[Gramzon_the_Dragon]

Copied from the wiki.

"Halflings
Halflings, more commonly known as demis, is a broad term for any sentient life form that shares physical traits with species outside of its own. The most famous example are so-called nekos, which are humans that underwent genetic alterations to gain cat ears and tails as purely an aesthetic trait. Later examples have spawned more practical uses, such as bear DNA being utilized by Soviet soldiers, or load baring animal DNA like horses or cattle enhancing the DNA of laborers. These so-called demis either underwent deliberate genetic modification, or were born with these traits from a genetically modified parent.
It is believed that the Skrell had some role in their creation, as some halfling societies pre-date human history, and there are a variety of common demis across the galaxy such as nagas (half-snake beings) that should not exist on the worlds they inhabit, as their evolutionary line doesn't connect with other life forms on the worlds they often live on.
Halflings continue to be developed even today for increasingly practical purposes. Advancements in genetic and xenoarcheological science has even allowed scientists to tap into the DNA of extinct life forms, which may result in even more hybrid options in the future."

TL:DR They at least were originally genetically modified from base species, and some are descendants of the sexually viable ones.