Tieflings, and all Planetouched races, use to be assumed to be planetouched subtypes of human, rules-wise. As far as I know, at least. Fluff-wise there's always been the extrapolated existence of non-human tieflings, but whenever such a thing has been rule-ified it's usually under a different name -- Fey'ri (elf/demon), Whispling (halfling/fiend), Tanarukk (Orc/Fiend) for example. I am not sure whether or not these are direct equivalents to tieflings, though, but they're similar.
Tiefling is a pretty broad concept. Baphitaur (Half-demon minotaurs, chosen by Baphomet), for example, were recognized as tieflings. Same with Durzagon (Half-Devil Duergar). Personally, I'd love to see the return of non-human versions of tieflings as playable races.
Originally Posted by Dexai
Anyway, this human-subtype assumption actually changed with 4th edition. Previously, tieflings did not breed true.
Not really. Until the 4th edition, tieflings could produce offspring with fiends, the result was cambions. By the way, cambions could also produce offspring. For example, Ravel from Planescape had a tiefling daughter, conceived by Cambion.
Originally Posted by Dexai
I think it's pretty fair to consider them no longer a type of human but their own race entirely.
