Zhang Dongzhu Group (Lanzhou University)
For over a century, we’ve had the opportunity to study Neanderthals – their bones, the artifacts they left behind, their distribution across Eurasia, etc. So when we finally got their genome sequences and discovered that we share a common genetic heritage with Neanderthals, it was easy to put that discovery in context. In contrast, we had no idea what Neanderthal genes looked like. Denisovans The discovery is a new one, as DNA analysis of a tiny finger bone reveals that yet another relative of modern humans recently roamed Asia.
Since then, we know very little. Their DNA is prevalent in modern human populations, suggesting they were likely concentrated in East Asia. But only bone fragments and a few teeth have been found since then, so we can’t even make an informed guess at what they looked like. On Wednesday, an international group of researchers described finds from a cave on the Tibetan plateau where the Denisovans lived, which can tell us a bit more about the hominins and tell us what they ate, which appears to have been whatever they could get their hands on.
Shiraishi Cliff Cave
The find was discovered in a place called Baishiyaya Cave, which is located on the northeastern cliffs of the Tibetan Plateau. As you can see in the photo below, it is located at an altitude of over 3,000 meters (about 11,000 feet) but adjacent to the plateau.
Oddly enough, the cave caught the attention of the paleontological community because it was a pilgrimage site for Tibetan monks. One of them discovered part of a lower jaw, which was eventually donated to the university. There, people struggled to understand exactly how it matched up with human populations, but eventually analysis of proteins preserved inside showed that it was Denisovan. Now, the cave is called “Denisova”. Xiahe mandibleIt is the most important Denisovan fossil ever discovered.
Zhang Dongzhu Group (Lanzhou University)
Since then, excavations at the site have uncovered numerous animal bones, none of which have been identified as Denisovan. But sequencing of environmental DNA preserved in the cave has revealed that the Denisovans had been periodically inhabiting the cave for at least 100,000 years, meaning they survived at high altitudes during both of the last two ice age cycles.
The new study focuses on bones, many of which are too fragmentary to definitively identify the species. To do so, the researchers purified protein fragments from bones, which contain large amounts of collagen. These fragments are then separated according to mass, a technique called mass spectrometry, which works on very small amounts of proteins that have survived for hundreds of thousands of years.
Mass spectrometry is based on the fact that there are only a limited number of amino acid combinations, often only one, that produce a protein fragment of a particular mass. Therefore, if mass spectrometry detects a signal at that mass, the possible amino acid combinations that produce that signal can be compared to known collagen sequences looking for matches. Some of these matches will be in places where collagen from different species has different amino acid sequences, and therefore it can be determined which species the bone came from.
The technique used in this method is called Zooarchaeology by Mass Spectrometry, or ZooMS, and in the case of the study described in the new paper, about 80 percent of the bone fragments examined were identified.
