RE: The line between -ism and science

Assuming you mean, for example, that the Norwegians would become brown-skinned and the Watusi fair-haired, no. Those characteristics wouldn't change (without interbreeding) in just a few generations.

Skin color is an example of natural selection. UV-A light destroys vitamin B folate in the skin. Our ape ancestors probably had light skin under their hair, but as we became increasingly less hairy, there was a survival advantage to be had from darker skin colors. As we migrated out of Africa into less sun-intensive regions, the pressures changed. Lighter skin gained a survival advantage by allowing more efficient production of vitamin D3.

The incidence is pretty low, but blondes occur in virtually every ethnic group - there are parts of Australia where over 90% of the aboriginal population are blonde. There are natural blondes among some groups of Pakistanis and Afghanis. The people of Azerbaijan have (relatively) a lot of natural blondes, too.

Obviously, with extensive interbreeding, the unique characteristics of the groups would disperse quite rapidly into the surrounding population, but without that, it would take hundreds, if not thousands, of generations.

Moreover, modern technology allows us to reduce or eliminate the genetic pressures that influenced skin color - vitamin deficiencies are easily addressed, and so they aren't likely to affect one's breeding chances. Our hypothetical population exchange might not result in any skin or hair color changes at all.

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