Our species’ origins may extend further back than previously believed, and the same could hold true for both our extinct Neanderthal and Denisovan relatives. A recent analysis of fossil remains suggests that the common ancestors of these groups emerged over a million years ago.

“If these ancient divergences are accurate, we might be overlooking significant details about the early history of these lineages,” states Chris Stringer from the Natural History Museum in London.

This finding could clarify the search for “ancestor X,” the lineage from which modern humans, Neanderthals, and the population that produced the Denisovans descended. It also may imply that the Denisovans were our closest relatives, potentially even closer than Neanderthals—a point that remains debated.

Stringer and his research team, which includes Xijun Ni from the Institute for Vertebrate Paleontology and Paleoanthropology in Beijing, revisited the Yunxian fossil collection located in central China.

Two partial skulls were unearthed on a terrace above the Han River in 1989 and 1990; reported in 1992. Both skulls were crushed during their discovery, although the YUNXIAN 2 specimen sustained less damage.

Using advanced techniques, Stringer, Ni, and their colleagues reconstructed the Yunxian 2 skull. These methods include CT scans that digitally separate individual bone fragments from the surrounding sediment. “The skull is elongated and has a prominent brow ridge,” Stringer notes. “Additionally, it features a slight beak-like nose, small third molars, and larger teeth.”

The Yunxian 2 skull dates back between 940,000 and 1.1 million years. Specimens of this age are often classified as Homo erectus, which appeared around 2 million years ago in Africa before dispersing to South Asia and Indonesia approximately 108,000 years ago. However, Stringer asserts that Yunxian 2 doesn’t conform to this profile; many of its features are characteristic of later specimens, including Neanderthals.

To better understand the Yunxian 2, the research team compared it with 56 other fossils of the same group. They constructed a family tree based on the morphology, grouping related fossils together. This analysis revealed three significant lineages, encompassing most fossils from the past million years.

One lineage consists of modern humans (Homo sapiens), another includes Neanderthals (Homo neanderthalensis) who lived in Europe and Asia for several hundred thousand years before disappearing around 40,000 years ago, and the third represents the Denisovans from East Asia.

Denisovans were first identified in 2010 through DNA from a bone fragment, and it took 15 years to connect this lineage with larger fossils. Stringer was involved in interpreting the Harbin skull from China, which was identified as Denisovan in June based on molecular evidence. Yunxian 2 appears to fall into the early Denisovan category, much like several other Asian fossils.

This discovery provides important links among these fossils in the Denisovan lineage, according to geneticist Aylwyn Scally at Cambridge University: “This allows us to form better hypotheses about the Denisovans’ whereabouts, lifestyle, and species characteristics.”

Recognizing that Yunxian 2 is a Denisovan reshapes our recent understanding of human evolution in two significant ways. First, it appears to alter the timeline of the emergence of these three groups. Traditional genetic narratives suggest that the common ancestor, “ancestor X,” diverged into two branches. However, the reconstruction indicates that Neanderthals separated first about 1.38 million years ago, before the divergence of modern humans and Denisovans around 1.32 million years ago.

If validated, this hypothesis posits that Denisovans were indeed more closely related to us than Neanderthals, challenging established genetic theories. Nonetheless, Scally expresses caution, noting the complexities of inter-group histories: “In reality, straightforward phylogenetic trees don’t provide a complete picture.” The research relies more on “entangled networks” than traditional models. Furthermore, Scally suggests that genetics may provide clearer insights into these relationships than morphology, especially with only partial skeletal evidence available.

The second significant change is that all three groups appear to have emerged much earlier than previously thought. Genetic evidence generally indicates that modern humans split from their Neanderthal and Denisovan relatives around 500,000-700,000 years ago. However, Yunxian 2 suggests that the Denisovan lineage was already distinct one million years ago.

Scally adds that there may not be a single definitive date for these splits; instead, they likely occurred over extended periods with intermittent separations and reunions. In this case, Stringer and his colleagues may be correct that divergence began over a million years ago, stretching across hundreds of thousands of years.

This extended timeline raises new questions. The oldest known fossils of modern humans date to around 300,000 years ago. So where are the earlier ancestors from millions of years ago? “We either lack those fossils, or they’re present but unrecognized,” Stringer comments.

We also know little about “ancestor X”—its appearance and habitat remain a mystery. “Ten years ago, I would have stated that the likely origin of most of these groups was Africa,” Stringer reflects. “It now seems plausible that their forebears lived outside Africa, potentially in regions of Western Asia. This suggests that ancient sapiens ancestors likely migrated to Africa, evolving there for a large portion of that million-year timeline.”

Stringer highlights the scarcity of known fossils from Western Asia dating back a million years, noting that even India has limited evidence. Only one human fossil from that period exists. “There are numerous regions where our fossil record is strikingly thin,” he asserts.

A significant source of information is the Yunxian site. In 2022, a third skull was uncovered that seems to be in better condition, although it has yet to be analyzed.

Neanderthals, Ancient Humans, Cave Art: France

Join New Scientist’s Kate Douglas on an enthralling journey through time as she delves into significant Neanderthal and Upper Paleolithic sites across southern France, from Bordeaux to Montpellier.