“This is the first time we have connected a cranium to Denisovans,” said evolutionary geneticist Qiaomei Fu, and in this way, a fossil discovery from a century ago in Harbin, China, lurked out of obscurity and entered the colorful world of evolution. The almost complete skull of this prehistoric creature, which has been nicknamed “Dragon Man,” has now been definitively associated with the so-called Denisovans, an unknown species of archaic humans.
For several decades, the Denisovans’ existence was known only via fossil parts. These included the Siberian Denisova Cave’s human finger bone, the Tibetan Plateau’s human jaw, and some human teeth. While providing genetic information, the fossils have done little to clear up the appearance of the Denisovans. But with the Harbin skull, estimated to be approximately 146,000 years old, we now have much more information. The Harbin skull has heavy brows, the like of which are usually associated with Neanderthals. However, its brain capacity, at approximately the same size as ours, is more like that of Homo Sapiens. The skull is approximately one foot long.
Extraction of DNA from these extinct remains is extremely hard. DNA is destroyed by warmth, water, and time. In this instance, the best possible DNA source, the hard petrous portion of the skull, had been extracted decades before. Fu’s team decided to focus on dental calculus, a calcified mineral deposit on teeth that serves as a micro-refuge. As seen in more contemporary research, this mineral deposit can retain host DNA well into forty thousand years ago despite composing only a small fraction of it. The protecting crystalline material prevents contamination and degradation of DNA, retaining an entire mitochondrial genome from the Harbin individual. It corresponded to the Denisovans’ Siberian DNA.
Along with DNA, the team isolated 95 ancient proteins from the fossil, of which three were Denisovan-specific proteins. Paleoproteomics, the analysis of ancient proteins, has proven to be an excellent tool in combination with genomics, especially in cases where DNA has degraded beyond recovery. Proteins are more resilient in their structure and take longer to degrade compared to DNA, allowing their preservation even after the DNA has exceeded the latter’s survival period. Mass spectrometry analysis enables the detection of amino acid sequence and post-translational modifications, offering valuable information regarding the evolutionary origin of the fossil, in this instance, confirming through protein “fingerprints” the DNA data, finally assigning the Dragon Man fossil to the Denisovan branch of human evolution, rather than being members of the homogeneous species, Homo longi.
Morphological and isotopic data indicate that Denisovans are likely to have been a muscular bunch. Their skull from Harbin would indicate a lean mass index of about 220 pounds. Their isotopic analysis would suggest a diet rich in animal proteins, possibly from substantial game sources hunted in cold grasslands. Evidently, their muscular build would require them to consume over 4,000 calories a day; this unlike their counterpart Neanderthals would suggest that Denisovans were even more mobile in their habitats that ranged from chilly Siberia to balmy Laos.
Analysis of genetic traits has shown that Denisovans contributed significantly to the genome of present-day humans. For example, the DNA of Papuans and Melanesians retains four to six percent Denisovan DNA, while the EPAS1 gene from Denisovans codeates the EPAS1 gene in Tibetan highlanders because of their unique adaptation to high oxygen intake. The above-mentioned example is the classic example of adaptive introgression. Denisova genes that code other traits include immunity, lipid metabolism, and resistance to viral infections.
The Harbin find is further reason to reconsider other Chinese discoveries, for example, those of Dali, Jinniushan, and Hualongdong, which have both ancient and modern characteristics mixed together on their bodies. Some may be regional Denisovans, instead of being classified as different species. Scientists are currently working on digital three-dimensional models combining data about Dragon Man’s physical characteristics and genetics to answer questions about his ability to walk, communicate, and interact socially.
Fu’s group is still attempting to extract nuclear DNA from the Harbin skull, and this might provide even smaller details, such as the shape and color of the eyes, resistance to certain diseases, and relationships to the Neanderthals. While this is going on, the proteomes are searching museums for additional remains of Denisovans, who were unnoticed in the museums. Further expeditions are also now underway to look for caves in Asia where the Denisovans might have dwelled.
Dragon Man’s Molecular Unveiling illustrates how improvements in ancient DNA sampling, the study of dental calculus, and protein sequencing are transforming the study of paleoanthropology. It’s a reminder that even the hard outer layer of a fossilized tongue-scraping tartar may conceal the secrets to rewriting evolutionary anthropology, another observer has pointed out.
