LordEntrails
Hero
Since you want to know about dragonborn...
In the FR setting;
Now, in the DragonLance setting, dragonborn are generally considered to the draconian race and they have a different origin story;
So let's go to other races.... well, at least in the earlier versions of the DragonLance setting, their were no half-elves or half-orcs, so no inter-species or inter-racial concerns there.
Now, in Greyhawk, half-elves and half-orcs exist, but other than saying that they are the offspring of human/elf or human/orc parents, nothing else is said. But of course as others pointed out, early sources indicate that with orcs breed with anything the result is almost always an orc. So maybe orcs are just bastards and mongrols, but again, it was never important enough for anyone to say much more than that.
So, again you said you are interested in all of this for world building, but are you rebuilding FR or some other setting? Are you building something new of your own? Then are you just looking for ideas? Because any answer you come up with is acceptable. Their is no single solutions. And finally, don't worry about it that much.
Honestly, decades ago I thought as you did, that to competently build a world, I had to have every detail worked out (though I admit I never worried about the offspring of inter-species intercourse). But you don't. And I will strongly emphasize that if you are going to this level of detail for your players, you are absolutely wasting your time. If you are doing it for your own edification, fine. But your players will not care. They won't. If you make a plot line or story interaction based around this, they will simple accept whatever you layout, whether it is "true" or not.
In the FR setting;
And the origins of the species;were a race of draconic creatures native to Abeir, Toril's long-sundered twin. During the Spellplague, dragonborn were transplanted from Abeir to Toril
or another view;Some legends of Abeir told that Io, the first and greatest of the dragon gods, created the dragonborn as servants for the first dragons.
The Platinum Cadre posited an alternative theory in their efforts to spread the worship of Bahamut, that the dragonborn were the ancient creations of the Platinum Dragon.
Now, in the DragonLance setting, dragonborn are generally considered to the draconian race and they have a different origin story;
So let's go to other races.... well, at least in the earlier versions of the DragonLance setting, their were no half-elves or half-orcs, so no inter-species or inter-racial concerns there.
Now, in Greyhawk, half-elves and half-orcs exist, but other than saying that they are the offspring of human/elf or human/orc parents, nothing else is said. But of course as others pointed out, early sources indicate that with orcs breed with anything the result is almost always an orc. So maybe orcs are just bastards and mongrols, but again, it was never important enough for anyone to say much more than that.
So, again you said you are interested in all of this for world building, but are you rebuilding FR or some other setting? Are you building something new of your own? Then are you just looking for ideas? Because any answer you come up with is acceptable. Their is no single solutions. And finally, don't worry about it that much.
Honestly, decades ago I thought as you did, that to competently build a world, I had to have every detail worked out (though I admit I never worried about the offspring of inter-species intercourse). But you don't. And I will strongly emphasize that if you are going to this level of detail for your players, you are absolutely wasting your time. If you are doing it for your own edification, fine. But your players will not care. They won't. If you make a plot line or story interaction based around this, they will simple accept whatever you layout, whether it is "true" or not.