First things first, Wes has final say on the details of the setting. Heck, I just recently discovered that I have been spelling "Nepleslia" wrong.
But, I do like to ramble on about the YSA universe, so here goes.
As I recall, the Nepleslians are genetically homo sapiens, who are descended from colonists from several other nearby star systems, many of which are no longer inhabited. The origin of these "humans", however, remains a mystery. No records of Earth exists, and the planet can not be found in current star charts. And no one could explain how a low-tech human civilization came to be on Fenyar (whose sun conveniently went super-nova recently).
Interestingly enough, the Nerimians, the YSA's extra-universal allies, do trace their origins back to a planet called Earth. That Earth, of course, is in
their universe. Just to make the whole thing even more confusing, the Nerimians are genetically homo stellaris (spelling?), a more evolved form, with more prevalence of psy abilities. (The Geshrin's psy abilities are genetically engineered, of course. And I think these abilities gets a little "boost" from the nodal system that Wes talked about.)
So, Nepleslians are just normal humans. Psy-abilities among them are very rare. They mostly rely on cybernetics to augment themselves. Lastly, female births are now extremely rare (p < 0.001?), due to an unfortunate genetic mutation in the human genome.
But the Empire has legions of catgirl soldiers to balance that out, so everyone's happy.