Around 900,000 B.E., the alien Cleax hordes invaded Starmourn and were only stopped by an alliance of the Utan Mir, the Y'saari, the Quix, the Ta-deth, and the Vyar.
As was only discovered later, during this invasion, they seeded Starmourn with genetic material that resulted in the evolution of both the Oteel and the Nath-el.
The Vyar subsequently built the Sheol Locus to keep the Cleax out of Starmourn in the future.