But let me continue on your path. Eugenics is artificial selection rather than natural selection. So you are suggesting the reason why there are vastly looking different populations in the world is because a everyone in that population decided what physical features they desired and only mated with people who had those features and in return those who did not possess those physical features were weeded out of the populations. I'll show you whats wrong with that scenario. Say if whatever artifically selected features in your eugenics scenario above were not beneficial to the environment, guess what...those people would die out. Say for instance if people in Europe were practicing eugenics for brown skin and therefore only mated with those who had brown skin and not those with light skin. That would mean the subsequent generations would have dark skin and that physical feature would perpetuate itself throughout the European populations. That sounds nice and dandy, but you're forgetting something very important...the environment! Dark skin before the days of Vitamin D enriched milk wasn't adapted for the cold and less direct sunlight in Europe. (If you'd like me to explain the connection between dark skin and Vitamin D deficiency I can, but I'll assume you this.) Therefore dark skinned people in these areas would develop severe cases of rickets leading to severe deformity and even death. Now tell me, if this eugenics thing you believed took place, do you think people were actively selecting for mates with rickets? I think not. People with rickets would have a very much less chance of mating and passing on their genes to future generations and consequently weeding out people with dark skin in colder climates. Nowadays, rickets is not a concern because people can get Vitamin D daily in their foods.
I don't know what point you are making about North Asians and Europeans. They look different and are both in cold climates. Like I said, all the variations in human appearance can't be explained, but both populations have light skin due to the Vitamin D deficiency - rickets things I just mentioned above. There are also people in equatorial environments that look different. Africans, Native Americans, Indians, South East Asians, Aboriginals, Pacific Islands, etc. The complexity in human appearance is obviously more than just skin color.