A skull found in the banks of the river Songhua in Harbin, China, has opened up a new debate on human evolution. The story of the discovery of the skull and the new findings are also stunning.
Almost 90 years ago, when Japanese soldiers occupied northern China, a local Chinese man was forced to help build a bridge across river Songhua. There on the river bank, the Chinese man found a treasure--a human skull. He stealthily took the skull and hid it in a well so that the Japanese soldiers could not find it.
Just few years back when the Chinese man was in his deathbed, he told his grandchildren about the skull. The grandchildren of the Chinese man retrieved the treasure and donated to GEO Hebei University’s Geoscience museum. Paleontologist Qiang Ji and his team conducted several analyses of the skull and they have published three reports comprising of the findings and their hypothesis as well. all the three reports have been published in the journal Innovation, which is a Cell Press partner journal.
In one of the reports, Ji’s team proposed that the skull belonged to an ancient human species; the team has termed the species as Homo longi. They also said that the new species, which they have proposed, was closer to modern humans than the Neanderthals.
Commonly known as the ‘Dragon Man’, the proposed new archaic human species has sparked new excitement along with a new debate among the scientists studying the evolutionary history of humans.
Some of the scientists and researchers in the field question the idea of a new species and the analysis done by Ji’s team on the human family tree. Some of them believe that the skull actually belongs to the Denisovans. The Denisovans were an archaic human species, which still remains elusive for the scientists. This species has been known chiefly from DNAs extracted from ancient samples. So, what the Chinese man hid in the well about 90 years back, could be the long-sought skull of a Denisovan.
Unfortunately, no geological context could be found for the skull; the Chinese man died before Ji’s team could ask him where exactly he found the fossil. Without any geological context, Ji’s team reached out to other researchers to help them date the skull. The nasal cavities of the skull had some sediments encrusted within and when analysed it was found that the sediment was linked to a specific layer of sediment around the bridge that the Japanese soldiers forced the Chinese man to build. This was dated back to between 138,000 years and 309,000 years ago. Uranium series dating also indicated that the skull should be minimum 146,000 years old.
After the dating, the team turned to identify which species the skull belonged to. Xijun Ni of the Chinese Academy of Sciences and Hebei GEO University led the task. The skull had a brain of size comparable to that of modern humans. However, it could not be a member of the modern humans or Homo sapiens as it had larger and square eye sockets, a wide mouth and a huge molar.
Ni’s team used computational methods and built a data set of over 600 possible traits of the skull, for example measurement of its length and brow size. Then they compared 55 traits taken from 95 other fossil skulls, teeth and jaws from the Homo genus, (The Homo genus consists of the modern humans, that is the Homo sapiens, along with other extinct species whose ancestors were closely related to the modern humans. For example, the Homo erectus, Homo neanderthalis).
The computer model organised the fossils into family trees (that shows evolutionary relationships among species). The tree that best fit the data showed four main clusters among the fossils. The new skull was found in a cluster that had several skulls belonging to China’s middle Pleistocene, which is a period that existed some 789,000 to 130,000 years ago. notably, during this period several other lineages of hominins existed.
More detail analysis of the new skull revealed an interesting fact. The skull was found to be most closely related to a jawbone found in the Xiahe Cave in the Tibetan plateau. Previous work on the jaw bone found in Tibetan Plateau showed that it was most closely related to Denisovans. This has led to many scientists believe that the newly analysed skull fossil of China could actually belong to Denisovans.
The China team has not attempted to extract DNA or proteins from the skull. However, their analysis also showed that the cluster of Chinese fossils were closer to early humans than the Neanderthals. Ni, commenting on the point, was quoted as saying—“ It is widely believed that the Neanderthal belongs to an extinct lineage that is the closest relative of our own species. However, our discovery suggests that the new lineage we identified that includes Homo longi is the actual sister group of H. sapiens.”
Other scientists, however, question the naming of a new species so early. Maria Martinon-Torres, a paleoanthropologist at the national centre for research on human evolution, Spain, commented: “It’s premature to name a new species, especially a fossil with no context, with contradictions in the data set.”