A Buddhist monk is trekking through the mountainous terrain of the Tibetan Plateau. At an altitude of more than 10,000 feet, he eventually comes to the opening of a curious cave. Here, he finds what appears to be the ancient remains of a jaw. The monk picks up the bone and determines to pass it on to someone with expertise in archaeology. And it’s a good job he did. After all, his find will one day shed light on a special genetic trait of the Tibetan people that has long baffled scientists.