As we look to the show more and more of the yaks are shown to us and i think i know what is happening and few other may put the dots in as well.

I think the Yak as a mix of our real-life Vikings and the Mongolian Empire, just think on what there both like.

They both share a warrior culture, both share the need to be the best, both share the ice cold climate. The last Key of all of this is that they both have Yaks as livestock.

What they show writers have done is just mix the two to make the Yaks.

That makes a lotta sense, except that the Mongols didn’t originate in the cold; the Mongols did most of their conquering from what would be the modern state of Mongolia.

well given there state is mostly in the high up and have lots of snow its still very cold

6533384
Actually yaks are not native to Scandinavia. Though there is a breed of cattle called the "Scottish Highland" that roughly resembles the yaks.
Click here to see.

6533475
huh neet! maybe in there world, they cross breed with each other and share each other culture

6533384
Given that yaks are native to the Himalayas and the Plateau of Tibet -- and the show's yaks living in cold, high mountains -- I tend to see them as a cross of Mongolian and Tibetan culture, myself.

Me too with some Viking culture mixed in.