Answer:
The EPAS1 gene is only common in Tibetan populations because it gives them a competitive advantage in high-altitude environments. People with the EPAS1 gene have more red blood cells, which can carry more oxygen. This allows them to breathe more easily and perform better at high altitudes. Over time, the Tibetan population with the EPAS1 gene has been able to survive and reproduce more successfully than those without the gene, leading to its increased prevalence in the population.