Evolution may be the ultimate last defense against invasion by other humans. The debilitating effects of altitude sickness seems to have prevented people native to low-lying areas from moving into high altitude regions, such as the Himalayas, according to recent research published in the journal Applied Geography. That study mapped how Tibetan villages continued up to a approximately 17,000 feet (5,200 meters) above sea level, but Han Chinese villages stopped at only 8,900 feet (2,700 meters).
On the other side of the planet, people who settled the Andes mountains evolved their own mechanisms to deal with high altitudes, according to a study published in the Proceedings of the National Academy of Science. Another study documented that descendants of Spanish colonists lack those adaptations and their offspring tend to be smaller than native Andeans.
Yet another ethnic group in the Ethiopian highlands evolved a third biological form of altitude tolerance. A collaboration of American and Ethiopian scientists suggested in Genome Biology that the Tibetans, Andeans and Ethiopians independently developed altitude adaptations in similar portions of their DNA, a phenomenon known as convergent evolution.