Tibet is one of the most hostile places that people inhabit. The weather is bitterly cold. The air is thin and dry.
But locals do well. First arriving 12,500 years ago, humans adapted to Tibetan conditions within 150 generations by introgression of Denisovan DNA suited to the habitat.
Admixture with other hominin species has provided genetic variation that helped humans to adapt to new environments. ~ American evolutionary biologist Emilia Sánchez et al