The Tibet plateau is a land of yaks and sherpas — and rapid evolution. Over a mere 3,000 years — a blink of an evolutionary eye — Tibetan highlanders have developed a unique version of a gene that helps them cope with life at extremely high altitudes, according to a study published Friday in the journal Science.
The research group, led by the University of California, Berkeley biologist Rasmus Nielsen, found the gene by comparing DNA from 50 Tibetans and 40 neighboring Han Chinese. The two groups are closely related, with one important difference: The Tibetans live at an elevation of at least 14,000 feet, while the Han population lives relatively close to sea level.
“The change at this particular position in Tibetan highlanders represents one of the most dramatic examples of genetic change in recent human history,” said University of Nebraska evolutionary geneticist Jay Storz, who was not involved in the study. “It really is a great story about how the human gene pool is still being shaped by the forces of natural selection.”
It makes sense that the harsh environment of the Himalayas promoted fast evolutionary adaptation. High altitude, with its lower levels of oxygen, is associated with reproductive difficulties such as miscarriages, low birth weight and increased infant mortality. In response, Tibetans have adapted in a way that may seem counterintuitive but is remarkably effective: lower blood hemoglobin levels.
Scientists still don’t know exactly how the low hemoglobin levels help the Tibetans, but they do know that too much hemoglobin makes the blood too viscous, making oxygen distribution more difficult. By maintaining hemoglobin levels about the same as those seen in normal people at sea level, the Tibetans have avoided this damaging effect.