Before revision: In the first case, this is apparently an adaptation to the extremely high UV irradiation on the Tibetan Plateau, whereas in the second case, the necessity to absorb UV radiation is alleviated by the Inuit's diet naturally rich in vitamin D. See also Allen's rule Bergmann's rule – correlating latitude with body mass in animals.
After revision: In the first case, this is apparently an adaptation to the extremely high UV radiation on the Tibetan Plateau, whereas in the second case, the necessity to absorb UV radiation is alleviated by the Inuit's diet naturally rich in vitamin D. See also Allen's rule Bergmann's rule – correlating latitude with body mass in animals.