1. I don't believe in all that evolution nonsense.

2. We're talking about TES, not earth, so I'm afraid I don't see your point.
Haha I had a very strong feeling you didn't

.
Well TES is made by people who live on Earth, so you can assume that some of the same rules apply. Culture and peoples change over time. Think about how different Americans and Canadians are from Europeans, e.g. French Canadians still speak French like it was in the 1800s, whereas the French speak a modern version of French. Likewise, think about how different New Yorkers are from Texans.
The Nords are the nordic peoples who scraqe a living in a very cold, harsh, dangerous and largely rural environment, whereas the Imperials live prosperously and comfortably in cities, surrounded by temperate environment. You would expect the two groups of people to be very different from each other, despite having the same ancestors.