In brief-ish:
- Goblins - bioengineered servitors brought to Earth by elves. Reproduce via skullstones, kinda like a seed, that also implants the next goblin with much of the memories/knowledge of the one the skullstone erupted from. Goblins themselves are pretty rare, and highly valued by human sorcerors who have the chutzpah to try and deal with one.
- Orcs/Hobgoblins (the same thing for me) - crossbreeds of elves and goblins made by the Atlanteans/Hyperboreans/Thulians/Mu/blah (haven't got a good overall name yet). Skullstones as well, but no memories/knowledge, probably (haven't really thought about it yet)
- Gnolls - I'm thinking they have to do something to mutate lesser canine/felines. I'm imagining my gnolls as back-engineered from an earlier carnivore form; miacids or something. They're not endemic to the area we're in, so, won't have to worry about it probably.
- Kobolds - more like malevolent gremliny earth elementals, animated by random chaotic ids (pretend that quantum fluctuations or other Star-Treky technobabble can spontaneously form a half-conscious ego, and animate some stuff. Same place I think giants and treants (tree-giants) come from - Gaia-Earth-Spirit sort of thing without the implied niceties)
- Bugbears - orcs and bears. I'm thinking about having them have bonuses to morale for purposes of Domains At War if you double-provision them in fall and let them hibernate (and as such you can only use them Spring through Summer) or a penalty if you don't...
- Ogres - devolved/degenerate Atlanteans/etc/etc. Ogre Magi, as a term, is applied to still-cognitive Atlanteans/etc. I'm kinda half-assed cribbing from Steven Erikson's Jaghut for my outlook on this sort of thing as an "elder race" from outside Earth.
- Others - extraplanar summons now living here as 'native'. I think most everything left (lizardmen, trogs, etc) are egg layers? Dunno if I've skipped anything.
It evolves. I'm running in large parts a quasi-historical game set in 1400s Poland, around Krakow, so I'm recasting/adjusting as I read more about the time period, fitting in things where it would make sense from a standpoint of much of the mythological history of the world being allegorical, or the true history being hidden and/or forgotten.
For example, I recently read 'Ibn Fadlan and the Land of Darkness', which in large part is about an Arab traveller WTFing at the weather and Norsemen in Central Europe. At any rate, something I'd forgotten - the old tale of the Gates of Alexander, and Gog and Magog, and all that, oft referenced in these sorts of medieval travelogues - easily decrufted and recast as an ancient general pushing back orcish hordes and their Hyperborean overlords back to Siberia, let's say.