Reconstructing the Denisovan Anatomy

After discovering the existence of a third taxonomic group, the Denisovans, among Neanderthals and Homo sapiens, scientists have been able to reconstruct a model of...

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Before the unearthing of ancient ancestral remains in a remote Siberian cave, scientists believed that only two taxonomic groups existed—Neanderthals and Homo sapiens. But 11 years ago in 2008, two major discoveries were made that ultimately challenged such ideas. A molar and a pinky finger were found in a cave in Russian Siberia, allowing researchers to expand upon the now-defunct theory. While the molar tooth and pinky finger are around 160,000 and 80,000 years old, respectively, scientists were able to sequence DNA from the fossils. What they discovered pointed to the existence of an entirely new group of humans: the Denisovans. The DNA provided valuable details regarding Denisovans, such as their intermingling and interbreeding with the first humans. They are now known to have lived in Asia, a theory proven true when it was found that modern-day Melanesians contain Denisovan-specific nucleotide sequences in their genomes.

Due to the lack of information concerning what Denisovan lifestyles consisted of and what exactly separated Denisovans anatomically from Neanderthals and Homo sapiens, scientists have continued to explore anatomical differences. A research team at the Hebrew University of Jerusalem has become the first to successfully extrapolate and reconstruct a model of what the first prehistoric relatives of humans may have looked like. This reconstruction is the result of almost a decade of puzzling over Denisovan facial features, yet it only gives a glimpse as to how one such Denisovan individual appeared. While data may be extrapolated to better understand what other beings living during this time looked like, researchers may need to unearth new pieces of fossil for further sequencing. Just a few years ago, the mere existence of the Denisovan taxonomic group separate from Neanderthals was something unexpected. Though only DNA evidence was available from the fossils, the technological developments leading to the reconstruction are extremely important. This is because the work furthers the question of what allowed humans to survive out of the array of hominins (not to be confused with hominids) that spread through ancient lands, a question that remains unanswered.

The reconstruction of the skeletal structure of the female to which the pinky finger belonged took years of tireless work and multiple cycles of trial and error. The researchers took DNA extracted from the finger, two Neanderthals, chimpanzees, and modern humans to use in a comparative study and learn more about Denisovan anatomy. The differences among methylation patterns in the DNA samples were amplified to separate unrelated anatomical features by a technique known as DNA methylation mapping. Methylation mapping is most commonly used to detect genetic differences between sample cells, usually in diseased and healthy tissue, or between genetically modified and unmodified material. In this case, however, such genomic patterns among species in the comparative study were used to find regions that were methylated differently. This allowed the research team to distinguish which genes result in certain anatomical features based on human illnesses in which the same genes lose their function. The patterns helped them understand what features were distinctly Denisovan, and around 56 of these features played an immense role in reconstructing their anatomy.

The DNA methylation technique was key in determining the differences between Denisovans and Neanderthals, but the physical anatomical reconstruction remained to be completed. The Denisovan fossils showed that their molars were largely unlike those in Neanderthals, and that their jawbones protruded but had no apparent chin. The pinky finger was similar to that of modern humans, indicating a common ancestor, while Neanderthals had evolved distinctive fingers. Experiments on the genomic information as well as extensive remodeling of the known attributes of Denisovans were what allowed scientists to come to such conclusions.

By using the data extracted from just a few Denisovan bones, a 3D sculpture of the Denisovan figure was created. However, there are still great limitations to what has been discovered regarding Denisovans. The collected evidence is not enough to determine what an entire taxonomic group may have looked like, and the reconstruction made is susceptible to massive changes if more information is ever unearthed. While the reconstruction may show what one specific individual may have looked like, the entire Denisovan category cannot be generalized as having the same characteristics as just one being. The reconstruction, however, is an important step toward accurately and completely mapping the human ancestry. The techniques used by the researchers may prove helpful to others attempting to reconstruct or picture organisms that have not presented much scientific data. One day, there may be a gallery of reconstructed ancient faces illustrating past relatives that scientists cannot reproduce today.