Until recently, it was thought that Homo sapiens and Neanderthals split off from their last common ancestor around 600,000 years ago, but a prehistoric skull from China has just shattered that narrative. Dated to a million years ago, the cranium belongs to an extinct human clade which encompasses the Denisovans, indicating that we had already branched off from our sister lineage prior to this point.

Discovered in Hubei Province in 1990, the so-called Yunxian 2 skull has been at the center of a taxonomic confusion for the past 35 years, largely because the specimen is badly crushed and therefore difficult to study. Due to its age and the shape of its braincase, though, some scholars had assumed that the cranium belonged to Homo erectus.

However, using CT scanning and digital reconstruction techniques, the authors of a new study have managed to correct the skull’s distortions and build a complete model of the specimen. In doing so, they revealed that Yunxian 2 possesses a mosaic of features, some of which are typical of more primitive hominins like H. erectus while others are more aligned with Homo sapiens.

Cross-referencing more than 500 of these morphological traits against 104 other human fossils, the researchers determined that Yunxian 2 belongs to the Homo longi clade, which includes a 145,000-year-old skull that was recently identified as a Denisovan. However, Yunxian 2 itself is not a Denisovan, but probably sits near the base of the lineage that gave rise to this enigmatic species. 

What’s more, while Denisovans and Neanderthals were previously thought to be sister lineages, the team’s analysis indicates that the Homo longi clade is in fact the sister group to the Homo sapiens clade.

“We really have to say we don't know where the common ancestor lived.”
— Professor Chris Stringer

“Because [Yunxian 2] is about a million years old, by definition, the Homo longi clade must be about a million years old at minimum,” said study author Professor Chris Stringer to IFLScience. “And that, in turn, implies that if sapiens and Neanderthals had already branched off, then their groups must be equally or even older in their origin.”

In other words, the Homo sapiens group must have emerged more than a million years ago, which is around 400,000 years earlier than certain genomic models suggest. Overall, the researchers estimate that our clade originated about 1.02 million years ago, while the Homo longi group dates back to 1.2 million years ago.