".... are adaptations to local environmental conditions"
THAT'S WHAT EVOLUTION IS !!!
Just like it sounds - "evolving" to meet needs!
Is it just co-incidence that dark-skinned people live in the tropics (where the sun is more intense) and fair-skinned people live in the north?
If all this could happen in the "mere" 5000 years or so since Adam, what evolving could happen over the SIX HUNDRED MILLION YEARS that higher life forms have been around? How about the billion years before that, when primordial life was around?
Evolution works, and is even consistent with God's Work.
THAT'S WHAT EVOLUTION IS !!!
I am aware of that. Your original post seemed to mix up the distinction between the classic racial traits and the genetic traits.
One can change environments and change many of the classic traits without similar changes in the deeper genetic traits, which offer a good track on descent. Skin color, on the other hand, correlates with environment and can change in a few thousand years. One of the best examples is the Native American migration to the Americas--there was a transition from cold to temperate to jungle (with high altitude an option at no extra expense) and then to cold for those who made the entire journey.
The mtDNA patterns can follow the exact line of this migration from Alaska to Tierra del Fuego, which many of the classic traits show considerable differences. One of the most notable is the high-altitude adaptations in the Andes--the Spanish did not do well up there.