Humans
From Oberon_wiki
By far the most common humanoid type on Terearth is “human” and it is this race that forms the basis of the Merebian Empire and many of the other lands on the planet.
Like many fantasy worlds, the humans of Terearth are physically compatible with most other medium-sized mammalian humanoids. Unlike other worlds, Terearth humans cannot impregnate (or be impregnated) by members of other races. This ensures that humankind, as a race, has never been “diluted” by other races.