A human skull unearthed in China’s Hubei Province in 1990, previously deemed too deformed to assess its significance, has now been identified as belonging to an early branch of a sister lineage to modern humans. This finding could significantly alter our understanding of human evolution over the past million years.

Using advanced scanning and digital reconstruction techniques, researchers analyzed the skull, estimated to be between 940,000 and 1.1 million years old, and compared it with over 100 other human fossils.

The study, led by paleoanthropologist Xijun Ni from Fudan University and the Institute of Vertebrate Paleontology and Paleoanthropology, suggests that the skull, known as Yunxian 2, is the oldest-known member of an evolutionary lineage that includes the Denisovans, who roamed parts of Asia and interbred with Homo sapiens.

The skull is believed to belong to a male aged between 30 and 40. Previously classified as Homo erectus, the new analysis indicates that it possesses features distinguishing it from this species. According to anthropologist Chris Stringer, the skull has a long, low shape with a receding forehead and a large estimated brain size for its age.

Despite suffering from partial crushing and distortion during fossilization, the skull shows similarities to other members of an Asia-centered hominin lineage that includes Homo longi and the Denisovans. Ni noted that it shares characteristics such as a broad mouth, flat cheekbones, and an expanded rear skull region.

The existence of Denisovans was first revealed in 2010, and since then, it has been shown that they, along with Neanderthals, interacted and interbred with Homo sapiens before their eventual extinction. Many modern humans, particularly those from Asia, carry Denisovan DNA due to this ancient interbreeding.

The research suggests that five major branches of large-brained humans began diverging more than a million years ago, leading to Homo sapiens, Homo longi, the Denisovans, Neanderthals, Homo heidelbergensis, and Homo erectus. Ni emphasized that the Yunxian 2 skull provides evidence that divergence among human lineages occurred earlier than previously thought.

The oldest-known Homo sapiens fossils date back about 300,000 years, but the findings imply that our lineage may have separated from other hominins hundreds of thousands of years earlier.

Stringer stated that this skull could be key to resolving the “Muddle in the Middle,” a term referring to the complex array of human fossils from 300,000 to one million years ago, suggesting that Yunxian 2 might offer critical insights into the evolutionary processes shaping our genus around one million years ago.