A 300,000-year-old ancient skull is different from any other human fossil ever found, according to researchers. This suggests there may be a new branch in the human gene tree.
The skull, or more specifically the lower jaw or mandible, which was unearthed by a team of international scientists from Spain, China, and the UK in the Hualongdong region in 2015, is believed to date back to the late Middle Pleistocene period.
The period, which began approximately 300,000 years ago, was pivotal for the evolution of hominins – species that are closely related to modern humans.
According to the study, which was published recently in the Journal of Human Evolution, the mandible, which has been named HLD 6, is “unexpected” in that it is different from all existing taxonomic groups.
Previously, scientists have also unearthed Pleistocene hominin fossils in China that have been difficult to classify. While they were originally thought to be anomalies, the recent discovery suggests that the evolutionary pattern may be different from what we had thought.
Comparing the Ancient Skull to other Skulls
In comparing the 300,000-year-old skull with those of modern humans and Pleistocene hominins, scientists have discovered that it has features of both.
More specifically, the mandible has the same shape as that of Homo sapiens, the modern human species that evolved from the archaic Homo erectus, which roamed the earth up to 1.6 million years ago. At the same time, it shares a key similarity with the Denisovans, a different branch that evolved from Homo erectus; that is, it appears to lack a chin.
According to Maria Martinon-Torres, one of the authors of the study, and the director of Spain’s National Research Center on Human Evolution, HLD6 “does not have a true chin”. However, it does have some “weakly expressed traits” that are often seen in Homo sapiens.
This makes HLD6 the first human skull to present a mosaic of primitive and modern Homo sapiens-like features.
Scientists believe that HLD6 must belong to a different species that has yet to be named. It also suggests that modern human features have been around as early as 300,000 years ago- before modern humans emerged in East Asia.
Researchers of the study also considered the age of the individual that the mandible belonged to. They were able to determine this by examining the skull shape, as it differs between adults and children.
It’s believed that HLD6 belonged to a young child, approximately 12 to 13 years of age. While the team didn’t have an adult skull to compare it with, they were able to look at those from the Middle and Late Pleistocene period. From that, they were able to determine that the shape patterns remained the same regardless of age.
However, they also emphasized that more studies and fossils are needed to determine their exact position in the human family tree.