Dire-wolves!

[ElBardo]

Yeah, well, as I said, having dreams and being a warg are two different things. Dany has a lot of revealing dreams herself and she is no warg as far as we know. Of course if Martin says they are, they are, but the books only show 1 skinchanging Stark. As for it being like a genetic passed-down power, a lot of families have Stark blood, even outside the North, so why just those 5 kids? Why not the Karstarks? They are pure male line Starks. Would seem it has more to do with how you are raised.

 

[Walshicus]

Yeah, well, as I said, having dreams and being a warg are two different things. Dany has a lot of revealing dreams herself and she is no warg as far as we know. Of course if Martin says they are, they are, but the books only show 1 skinchanging Stark. As for it being like a genetic passed-down power, a lot of families have Stark blood, even outside the North, so why just those 5 kids? Why not the Karstarks? They are pure male line Starks. Would seem it has more to do with how you are raised.

Jon and Arya are pretty explicitly shown warging through their dreams, Rickon and Rob to a lesser extent. Pretty sure there's something with Sansa too...

 

[ElBardo]

Sansa never dreams any wolf dream that I recall. Rickon probably has greendreams, as he sees future events, but i can't remember any wolf dream he mentions, same with Robb. I am currently re-reading the novels tho', long time since I read them.

 

[matsunaga]

The stark bloodline is two thousand years old or some such? i also remember reading somewhere that pretty much every stark has warg potential.

 

[Furion Matsuya]

The stark bloodline is two thousand years old or some such? i also remember reading somewhere that pretty much every stark has warg potential.

8000 years old maybe more although as Sam has noted, things don't entirely make sense with the histories so the length is more likely somewhere between 6000 or 4000 years.

 

[Wilokers]

I think that the Stark's warging abilities originate from when they defeated the Children of the Forest and the Warg King, and took the Warg King's daughters as prizes.

http://awoiaf.westeros.org/index.php/Warg_King

That and/or because GRRM wills it

 

[Clear Air Turbulence]

The people who can get the traits are the old gods religions including beyond the wall with the addition of the farwynds and westfords.
Why would it be hereditary?

In the distant past the Starks defeated the warg king and then killed all their men and raped their wives and daughters to produce young with stark blood and warging abilities.