Why don't Tibetans feel lightheaded this high above sea level? It's in the genes.
Why don't Tibetans feel lightheaded this high above sea level? It's in the genes. iStockphoto.com
Darwin might have been impressed with this one: A group of scientists in China, Denmark and the U.S. recently documented the fastest genetic change observed in humans.
According to their findings, Tibetan adaption to high altitude might have taken just 3,000 years. That's a flash, in terms of evolutionary time, but it's one that's in dispute.
The most dramatic genetic mutation was found in almost 90 percent of modern day Tibetans, but less that 10 percent of Han Chinese. (The Han is the majority ethnic group in China. Tibetans split with them thousands of years ago.)
It's the gene that seems to help the Tibetans live comfortably in the oxygen-scarce environments they call home, 4,000 meters above sea level.
The mutation occurred in a gene called EPAS1, which plays a role in how the body responds to low oxygen conditions and how athletes take in oxygen during exercise.
But it's not just one little change. The researchers found mutations in about 30 genes that had become more common among Tibetans than among the Han.
"Each [mutation] has a small effect but as time passes, it can lead to drastic genetic changes," explained Rasmus Nielsen, an evolutionary genomics expert on the team.
Over the course of 120 generations, Nielsen says you can now see the changes — Tibetans have just as much oxygen in their blood despite low levels of the oxygen-carrying protein hemoglobin.
As thought provoking as the study is, some archeologists say the time frame of Tibetan evolution is impossible.
“The separation of Tibetans and Hans at 3,000 years ago is simply not tenable by anything we know from the historical, archaeological or linguistic record,” Mark Aldenderfer, a Tibetan expert at the University of California, Merced told the New York Times. He says the split was 6,000 years ago or more.
But Nielsen says that his team's findings reflect the adaptation of modern day Tibetans who are descendants of those who migrated to the plateau more recently.
The results are published in Science.