Clearly, the people of Tibet must have evolved quickly to tolerate a life spent living at the top of the world. How quickly? A study out in this week's Science, which compared Tibetans to Han Chinese to see the differences in their DNA, says that the two groups may have diverged no more than 3,000 years ago. If natural selection has changed Tibetans in such a short time, it would be the fastest known example of human evolution. But not everybody is buying this time line. As DISCOVER noted when a similar study by another team came out in May, natives of the Tibetan plateau seem to survive the altitude because their bodies make less hemoglobin. It's somewhat counter-intuitive:
In theory higher levels of haemoglobin would be beneficial, because this would improve oxygen transport. But high levels could make the blood thicker and less efficient at carrying oxygen, says Jay ...
