A newly analyzed skull from China, estimated to be around 1 million years old, has the potential to reshape our understanding of human evolution. The specimen, known as the Yunxian 2 skull, has been linked to an early Asian hominid lineage that led to the now-extinct species Homo longi, according to research published on September 25, 2023, in the journal Science. This breakthrough was achieved through a digital reconstruction that corrected features of the skull which had been distorted during the burial process.
Researchers led by Xiaobo Feng from Shanxi University in Taiyuan, China, view the findings as a new framework for understanding the complex array of Middle Pleistocene hominid fossils. These fossils, dating between approximately 789,000 and 130,000 years ago, have long puzzled scientists trying to place them within the human evolutionary tree. The team suggests that the evolutionary relationship between ancient hominids, including Homo longi and its ancestors like Yunxian 2, may be closer to that of modern humans than to Neandertals.
In a significant twist, the study proposes that the Denisovans, often seen as distant relatives, are actually part of the H. longi lineage, indicating they share a closer connection with modern humans than Neandertals do. Despite these exciting revelations, the complexities of human evolution remain deeply challenging.
“While it’s exciting to have a corrected version of Yunxian 2, Middle Pleistocene evolution represents an enduring mystery,” stated Sheela Athreya, a paleoanthropologist at Texas A&M University. Athreya, who did not participate in the study, noted that the varying skeletal traits of Yunxian 2 and other Homo fossils complicate efforts to classify them into distinct evolutionary lineages.
The discovery of the Yunxian 2 skull occurred during excavations at a riverbank site in central China. Initially, a badly damaged skull, known as Yunxian 1, was unearthed in 1989, followed by the discovery of Yunxian 2 in 1990 and Yunxian 3 in 2022. The age of these fossils was estimated using geological data, including reversals of Earth’s magnetic field and the remains of extinct animals found in the same sediment layers.
The Yunxian 2 skull presents a unique combination of features. It has a long, low braincase that housed a relatively large brain, while certain traits, such as narrowly spaced eye sockets and a wide, flat nasal opening, link it to Homo longi. To determine Yunxian 2’s evolutionary lineage, Feng and his colleagues analyzed it alongside 104 other hominid skull and jaw specimens from various regions, including Africa, Asia, and Europe. Using computer analysis, they constructed evolutionary trees that clarified the relationships between different lineages.
The findings suggest that the ancestors of H. longi, including Yunxian 2, shared a common ancestor with modern humans approximately 1.32 million years ago. This builds on recent genetic studies indicating that two ancestral populations of contemporary humans diverged as early as 1.5 million years ago. Furthermore, fossils from Europe, classified as Homo antecessor and dating between 900,000 and 800,000 years old, may also belong to the H. longi lineage.
According to Feng’s group, the first members of a separate line leading to Neandertals appeared around 1.38 million years ago. If validated, these relationships suggest that modern humans have closer evolutionary ties to the ancestors of H. longi than to Neandertals.
“If the Yunxian 2 skull provides a glimpse of Homo anatomy shortly after the origins of both the H. longi and H. sapiens lineages, it may represent one of the most important windows into evolutionary processes that shaped our genus,” said Chris Stringer, a paleoanthropologist and co-author of the study at the Natural History Museum in London.
As the scientific community continues to analyze these findings, the Yunxian 2 skull stands as a pivotal piece in the intricate puzzle of human evolution, prompting further investigation into our distant ancestry.