This isn't really relevant to ESO, since beyond a few individuals being explicitly NOT Dragonborn (most importantly for us the player character and the Prophet) it doesn't really come up in this game, but it's something I've been wondering about.
As I understand it any individual could be Dragonborn - contrary to popular belief they don't have to be a descendant of St. Alessia and it's unclear if they are actually related to dragons in any way (biological, spiritual or otherwise) or simply have similar innate abilities, so even if it was possible to trace everyone's lineage back to the dawn of time it wouldn't necessarily help identify them.
So far we know of just two ways to find out if a person is Dragonborn:
1) They kill a dragon and absorb it's soul. (Or rather they're present when it dies, once in Skyrim I was chasing a dragon but I don't think I ever even hit it, then some giants killed it and I still got the soul.)
2) They use the Amulet of Kings to relight the Dragonfires and seal Nirn away from Oblivion.
These methods are, to put it mildly, impractical. The first because throughout the majority of Tamriel's recorded history there have been no dragons to fight, and because even when there were it involves finding and defeating a dragon, which is pretty demanding just to check if you possess a particular kind of magic. The second is considerably worse given what can happen if the person attempting it is not Dragonborn. (Which is basically the opposite of the intended effect, and the setup for ESO's main story.)
Given that throughout history a succession of individuals, some of whom had fairly dubious claims, have used the Amulet of Kings to light the Dragonfires it seems like there should be some way to check in advance whether it's going to work. Or was it really left to chance/trusting they are who they say they are all those times?
I think in a way it would make more sense if it was Akatosh choosing to give that power to someone, so all the Emperors who successfully lit the Dragonfires just had to convince him they were worthy. Pretty harsh that he'd allow the Soulburst to happen, but maybe letting Varen become Emperor and go on trusting Tharn and Mannimarco would have been even worse?
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