We don't know. They are mortals given the powers of Dragons by the gods. We don't know if our lineage was special, or if it was just that the Gods decided to make you Dragonborn.

The Nerevarine was called "Dragonborn", but that could have had a different connotation, such as "Born under the Dragon", i.e., born under the Empire. We can assume that the Champion of Cyrodiil was NOT Dragonborn, because he was unable to wear the Amulet of Kings.

If it's a matter of lineage, that's fine, but your ancestors would have known they had it. From what it sounds like, being Dragonborn isn't just something that you just randomly discover. It's a really, really big deal.

Some people here seem to be mixing old theories of Dragonborns (which they came up with before Skyrim) with new info.
Judging by the info from GI, the Dragonborn were Dragon Hunters and their powers seem to have been inheritable. In past there were more of them but now for some reason only few remain. Septims seem to be one of those Dragonborn families, but probably not the only one.

However, powers of Dragonborn seem to mean little if you are not trained on how to use them. So a Dragonborn without training is just a little better then other members of his race.

What Dragonborn are exactly is unknown: they may be descendants of people who were somehow blessed or they may have been descendants of Elfoney that have been Dragonborn. Or maybe gods create them? It is still unknown for now.

Quote form the game informer article about the dragonshouts : "The dragonborn are a unique group of mortals, gifted by the gods with the same power as the dragons."
So, no interbreeding with the dragons, not necessary a blood of Septim and no fixed race or origin. It's just a "divine blessing" of a kind, end of story.

Almost nothing written in GI is "end of story" and certainly not something as vague as that.

What exactly is so vague about that statement? It's as clear as it gets, I don't see any room for misinterpretation here... It's not a "player had dragonblood", it is not "distant cousin of Septim line". It is a power bestowed by the gods on selected mortals, not much room to wiggle is it? Wile you may try to cook up some impossible stories about the subject the devs obviously cleared the point for themselves quite nicely.

I though it was the Blades who were the dragon hunters instead of the Dragonborn. I have to look for that quote again.



According to http://www.imperial-library.info/content/races-tamriel-nord, Kyne's daughters taught the Nords thu'um so she might be responsible for the Dragonborn:



EDIT: I misremembered. The Blades were the dragonguard and the Dragonborn are dragon hunters as you said.

Mankar Camoran wears the Amulet of Kings and has no relation whatsoever to the Septims. Dragonborns are not septim family only.

Because "player has dragonblood" and "player is a distant cousin of the Septim line" can both be seen as "player is gifted by the gods", and the same article refers to them as a "storied line of mortals" which seems to imply inheritance, not direct intervention on an individual basis. It also says that Dragonborn can "light the dragonfires to become the emperor" which also implies a connection to the Septim line. It refers to the Septim line as "one ancestry of dragonborn individuals". The very name "Dragonborn" implies an element of ancestry.

According to the quote, the anointment by the gods is why the dragonborn can light the dragonfires so any dragonborn would do.



Since the Septims were just "one ancestry of dragonborn individuals", it implies that the current dragonborn hero might not be related.

Yes, but it implies that it is a family ancestry. So distantly related is possible, depending on where and how the line began.

Sshodan's line of "It's just a "divine blessing" of a kind, end of story." sounded to me like (s)he envisioned a god appearing before random individuals and saying "poof, you're a dragonborn".

Even if that wasn't meant. "It's just a 'divine blessing' of a kind" is hardly the end of the story of what exactly a dragonborn is.

Why not? If some gods created the first dragonborn lines, why can't they create some more?

At the moment, it does look like it will probably be "in the blood" of the player's character. I highly doubt they will tie your character to the Septims though.

So, assuming this has to do with bloodlines, why did the Septims after Talos neglect their Thu'um abilities? Or didn't they?

They were too busy to go to Skyrim?

That may be part of it. The player learns them as he goes. "There are others in the world who can use the Dragon Shouts, but it's rare", so some of the words are known, in less powerful forms.

Of course, having absolutely no dragons to fight or harvest souls from, the Dragon Shouts and any other powers probably became less and less important.

Or there's a conspiracy to eliminate all knowledge of them, similar to conspiracies in past ES games.