Zhang Dongju (Chinese: 张东菊) is a Chinese archeologist and an associate professor at the College of Earth and Environmental Sciences of Lanzhou University. Her research determined that the Xiahe mandible found in the Baishiya Karst Cave on the Tibetan Plateau shared DNA with fossilized remains found in the Denisova Cave in Siberia, moving the dates of earliest proven hominin activities in the Tibetan Plateau to 120,000 years earlier and showing for the first time that the Denisovan hominins had spread throughout Asia rather than being located only near the Denisova Cave. Her work is considered likely to prompt reconsideration of other fossil remains using ancient protein analysis.
Zhang studied at Shandong University from 2000 to 2004 and graduated with a bachelor's degree in archeology. From September 2004, she pursued graduate studies at Lanzhou University, where she joined the group of climatologist Chen Fahu. Her main research focus was on the Paleolithic sites of the Loess Plateau. She was a visiting scholar in the Department of Anthropology at the University of California, Los Angeles in the United States from January 2008 to September 2009, and then at Römisch-Germanisches Zentralmuseum in Germany from October 2009 to March 2010. She earned her Ph.D. in physical geography from Lanzhou University in December 2010.
After earning her Ph.D., Zhang became a faculty member in environmental archeology at Lanzhou University. She changed her research direction from the Loess Plateau to the Tibetan Plateau, and began to study the Xiahe mandible, together with her former advisor Chen Fahu. The Xiahe mandible is a fossilized jawbone found in 1980 by a monk in the Baishiya Karst Cave, which is located in Xiahe County on the northeastern edge of the Tibetan Plateau, 2,250 kilometres (1,400 mi) from the Denisova Cave where the only other known Denisovan remains have been found. It was donated to Lanzhou University. According to Zhang, the Xiahe mandible was so "weird" that Lanzhou researchers could not classify it, and it was overlooked for thirty years.
Zhang investigated the discovery of the mandible by interviewing local people in Xiahe. They told her of human bones found in the cave. When asked in 2019 whether it was possible the story wasn't true, she said, "I don’t think the local people would lie about this.” Because the provenance is uncertain, the research team in 2019 acknowledged they could not prove the fossil came from the Baishaya cave, but they were able to match minerals on the Xiahe mandible to mineral deposits in the cave.
The mandible did not yield any DNA, but in the dentine of the teeth they found collagen proteins. In 2016 Zhang and her colleagues started working with Jean-Jacques Hublin of the Max Planck Institute to use ancient protein analysis.
Also in 2016 local villagers and Buddhists gave Zhang permission to start archeological work within the cave, which is a Buddhist sanctuary. Again with local permission she led a team to begin excavation in and around the cave in 2018, digging two trenches in which they found animal bones with cut marks and a large number of stone tools. In 2019 Zhang told Science, "We do hope we'll find more Denisovans."
Importance and impact
Denisovan DNA is found in modern humans across Asia and Australasia, but Zhang's work connecting the Xiahe mandible to the Denisovans is the first evidence that Denisovans lived anywhere but in the Denisova Cave area. It is also the first evidence they lived at high altitudes, as the Denisova Cave is only 2300 feet (700 meters) above sea level. The Baishiya cave is 10,760 feet (3280 meters) above sea level. Denisovan DNA, specifically the EPAS1 allele, has been considered to be what allows Sherpas and Tibetans to live at high altitudes in low-oxygen environments. The Xiahe mandible is considered likely to be the oldest hominin fossil on the Tibetan Plateau. Zhang told The Paper "this study will push the history of prehistoric human activities on the Qinghai-Tibet Plateau from 40,000 years ago to 160,000 years ago."
Zhang's classification of the Xiahe mandible as Denisovan is likely to cause scientists to reconsider the classification of other remains using the methods she and her colleagues used.
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