OLDEST EVIDENCE OF HUMANS ON TIBET PLATEAU

When she and her colleagues made a small excavation in the cave, they found ancient tools, a sign of human occupation. She emailed photos of the jaw to Jean-Jacques Hublin, a paleoanthropologist at the Max Planck Institute. Intrigued, he traveled to China to examine the fossil, and soon he and Dr. Zhang had begun a collaboration with other experts to learn more.

Chuan-Chou Shen and Tsai-Luen Yu of National Taiwan University handled the task of figuring out how old it was. The jaw still had bits of rock stuck to it, and these contained uranium. By measuring the uranium’s decay into thorium, Dr. Shen and Dr. Yu were able to estimate the bone’s age. The jaw turned out to be at least 160,000 years old, by far the oldest evidence of humans on the Tibetan plateau. Its antiquity also supported the scientists’ hunch that it did not belong to our own species. The proteins were not from modern humans; instead, they were a match to Denisovan DNA from Siberia.

With the new discovery and other recent finds, a picture of the Denisovans has grown clearer. Everything about their heads seems to have been big, from their giant molars to their thick jaws to their massive brain cases. Dr. Viola speculated adults may have weighed well over 200 pounds. “I’d assume they’d be very large and robust individuals,” he said. “These are like football players.” The discovery of Denisovans living at high altitude is intriguing for another reason: Tibetans today share a special genetic link to Denisovans.