User blog comment:Jack Pistol/Immortal Dovahkiin?/@comment-6326997-20130205183434

Theory I:

The Dovahkiin was created by Akatosh just as Alduin and Paarthunax were. In a since he is his "Son" in my opinion. The Slave Queen 's blood was given to her by Akatosh and thus in a sense she was born to him. Since then that same dragon soul has dwelled in different mortal bodies. That is why it can be any and everyone.


 * Spoiler*

As one comment said, the Dragonborn emperors were bound to the Amulet of Kings and thus the line may have been kept there for so long because of it.

Theory II:

But now the Dovah are able to roam free and do as they please, it is very possible that the Dragonborn actually has multiple "Sibblings" the other Dovahkiin.

At any rate it is fitting to say that in theory the Dragon soul cannot die and does not enter Sovngarde upon it's mortal death as no other Dovahkiin were found within the Nordic afterlife (Not even Martin Septim or any of the Septim /Reman Emperors .)

Theory III:

My final theory is that the Dragon Soul is actually a piece of Akatosh himself. And is therefore not Immortal because the Aedra are no longer immortal. They can "die" in a sense. But as stated before me, spirits are already immortal because they cannot die a second time. The spirits that Alduin absorbed were just that. Absorbed into him and either became part of him, or were held captive in his body/soul.

Conclusion:

In sumnary the true likeness of the Dragonborn can only be defined by that which Bethesda has chosen to reveal to us. In that way we know the Dragonborn has dragon blood and a dragon soul, and thus he/she is part dragon in at least two ways.