What causes a person to have a gene that causes that person to produce 50 percent more hemoglobin than the average person?

A person may have a gene that causes them to produce 50 percent more hemoglobin due to genetic mutations or variations in specific genes related to hemoglobin synthesis, such as those affecting the globin chains. These variations can be inherited from parents or arise spontaneously. Environmental factors, such as living at high altitudes where oxygen levels are lower, can also influence hemoglobin production as the body adapts to increased oxygen demand. Such genetic traits can confer advantages in oxygen transport and utilization, particularly in challenging environments.