A newly reconstructed skull, known as Yunxian 2, dating back approximately 1 million years, has the potential to reshape our understanding of human evolution. Researchers, led by paleoanthropologist Xiaobo Feng from Shanxi University in China, have determined that this ancient hominid skull belonged to an early member of a lineage that eventually led to a now-extinct species called Homo longi. The findings were published on September 25, 2023, in the journal Science.
The Yunxian 2 skull underwent a digital reconstruction to correct features that had been damaged during burial. Feng and his team view their results as a framework for re-evaluating a complex array of Middle Pleistocene hominid fossils, which date from approximately 789,000 to 130,000 years ago. Notably, the research suggests that an ancient line of hominids leading to modern humans may have had a closer evolutionary relationship with H. longi and its predecessors than with Neandertals.
Significantly, the study also presents Denisovans as part of the H. longi lineage, indicating they may be closer relatives to modern humans than to Neandertals. This revelation adds a new dimension to ongoing debates about human evolution, which remain complex and often contentious. According to paleoanthropologist Sheela Athreya from Texas A&M University, while the reconstruction of Yunxian 2 is exciting, Middle Pleistocene evolution continues to be a perplexing puzzle.
Feng’s team points out that the Yunxian 2 skull displays an unusual mix of skeletal traits, complicating its classification. For instance, the skull features a long, low braincase that accommodates a relatively large brain, yet some characteristics, such as narrowly spaced eye sockets and a wide, flat nasal opening, link it to H. longi.
To establish the evolutionary lineage of Yunxian 2, the researchers analyzed this specimen alongside 104 other hominid skull and jaw samples from various continents, including Africa, Asia, and Europe. Using computer analysis, they generated evolutionary trees that clarified the distribution of different skeletal traits, allowing them to estimate the timing of common ancestors for these lineages.
The findings suggest that the evolutionary predecessors of H. longi, including the Yunxian 2 specimen, shared a common ancestor approximately 1.32 million years ago with a lineage culminating in modern humans. This timeline aligns with recent DNA analyses indicating that two ancestral populations of contemporary humans diverged as early as 1.5 million years ago. Additionally, the researchers propose that European fossils, often classified as Homo antecessor and dating between 900,000 and 800,000 years, may also be part of the H. longi lineage.
Feng’s group estimates that the earliest members of a distinct Neandertal lineage emerged around 1.38 million years ago. This suggests that modern humans had closer evolutionary ties to the ancestors of H. longi than to Neandertals. As Chris Stringer, a paleoanthropologist and co-author of the study from the Natural History Museum in London, states, if the Yunxian 2 skull offers a glimpse into the anatomy of hominids shortly after the emergence of both H. longi and modern human lineages, it may represent a crucial insight into the evolutionary processes that shaped our species.
The significance of the Yunxian skulls is further highlighted by their discovery history. Excavations at the Yunxian site along a riverbank in central China began in 1989, uncovering a badly damaged skull designated as Yunxian 1. Subsequent digs revealed Yunxian 2 in 1990 and Yunxian 3 in 2022, the latter of which is still awaiting published analysis. Dating these fossils has been aided by previous studies of Earth’s magnetic field reversals and the bones of extinct animals found in proximity to the skulls.
As research continues, the relationships between Yunxian 2, Denisovans, and the proposed H. longi fossils remain poorly understood, according to Athreya. Nevertheless, the findings presented by Feng and his colleagues set a foundation for future exploration into the intricate web of human ancestry, potentially offering answers to longstanding questions about our origins.
