A 300,000-year-old ancient skull, unlike any other premodern human fossil discovered to date, is challenging standard theories of human evolution, suggesting a possible new branch in the human family tree. This finding is a result of the diligent work of an international team of researchers from countries including China, Spain, and the United Kingdom.
The team discovered the skull, specifically the lower jaw, also known as the mandible, in the Hualongdong region of eastern China in 2015. The site yielded 15 other specimens, all of which are believed to come from the late Middle Pleistocene period, a critical time for hominin evolution—hominins being species known to be closely related to humans, including modern humans.
The study of the mandible, labeled as HLD 6, was published in the Journal of Human Evolution on July 31. The research established that the fossil defied categorisation, failing to correspond with any existing classifications.
China's ancient Pleistocene hominin fossils have been enigmatic, often disregarded as anomalies when found previously. However, recent research is gradually redefining general concepts of the evolutionary timeline in the late Middle Pleistocene, hinting that there might be more to the story.
Analysts stumbled upon an intriguing combination of characteristics when comparing the HLD 6 mandible with those of Pleistocene hominins and modern humans: HLD 6 showcased a mix of both. The fossil shared a similar shape with the mandible of Homo sapiens, which evolved from Homo erectus, our modern human species. However, HLD 6, reminiscent of a different branch that evolved from Homo erectus, the Denisovans, lacked a chin.
“HLD6 does not present a true chin but has some weakly expressed traits that seem to anticipate this typically H. sapiens feature,” noted María Martinón-Torres, director of the National Research Center on Human Evolution (CENIEH) in Spain. She stated that the Hualongdong fossils are "the earliest fossil population known in Asia to present this mosaic of primitive and H. sapiens-like features."
Based on these findings, the researchers propose that HLD 6 belongs to an unnamed classification - one that signals modern human traits as early as 300,000 years ago, well before the appearance of modern humans in East Asia.
Additionally, the team took into account the age of the individual linked to the jawbone to determine whether skull shape variations were due to age differences. They concluded that HLD 6 likely belonged to a 13-year-old individual, and after comparing the skull shape to similar-aged and adult skulls from the Middle to Late Pleistocene, they found consistency in shape patterns.
However, according to Martinón-Torres, the final classification for HLD 6 is not settled yet. She said more research and fossils are needed to "understand their precise position in the human family."
