Homo erectus is considered to be the first human species to leave Africa and colonize Eurasia. However, when this happened is disputed. Now a new dating of three Homo erectus skulls discovered in China provides new clues. Accordingly, these finds are already 1.77 million years old – 800,000 years older than previously assumed. This makes these skulls from Yunxian the oldest reliably dated evidence of Homo erectus in East Asia, as the researchers report. In their opinion, this suggests that early humans could have spread across Eurasia more quickly than expected. This could also clarify the mystery surrounding some stone tools from China that are dated to more than two million years ago and whose creator is still unknown.
Homo erectus was one of our most successful ancestors. This early human tamed fire, made the hand axes of the Acheulean culture and was the first representative of our species to leave Africa and settle on other continents. But where and when the first Homo erectus emerged and how quickly it then spread across Eurasia is unclear. The oldest Homo erectus find in Africa to date is the skull of a child discovered in South Africa, which is around two million years old. The oldest fossils of this early human from Eurasia are around 1.8 million years old and come from Dmanisi in Georgia. Although several Homo erectus fossils have also been found in East Asia and Southeast Asia, most of these date from around a million years ago and are therefore significantly younger.
How old are the three skulls from Yunxian?
This was also assumed for three early human skulls from the Yunxian site in the Chinese province of Hubei. Two of these skulls were discovered in the 1970s, but were badly crushed, so that their classification as a species initially remained unclear. “However, recent excavations at the site led to the discovery of a third, relatively intact skull located around 345 meters away from the first two skulls,” report Hua Tu from Shantou University and his colleagues. According to initial investigations, this shows clearer features of Homo erectus, but the more detailed analysis has not yet been completed. Several hundred stone chips and other traces of human activity were also found at the same location. According to the first paleomagnetic dating, the skulls came from around 870,000 to 830,000 years ago. Uranium dating of animal teeth from the same layer suggested an age of around one million years. However, all dates were subject to great uncertainty, as the paleontologists explain.
That’s why Tu and his team have now re-dated the finds and chosen a different method: They analyzed the cosmogenic isotopes beryllium-10 and aluminum-26 in the quartz grains of the find layer sediments. These rare, radioactive types of atoms are formed when minerals on the Earth’s surface are exposed to cosmic radiation. Their proportion can therefore reveal when a rock layer was last on the surface – and thus also the age of the fossils found in it. “The use of this dating method can therefore help us to obtain an independent and robust age definition for the Yunxian finds,” explain the researchers. It is particularly suitable there because the layer sequence in this site is undisturbed and easily recognizable.
Rapid spread across Eurasia
The new dating revealed that the three early human skulls from Yunxian are considerably older than previously thought. Tu and his colleagues determined that they were around 1.77 million years old. “According to this dating, the Homo erectus fossils from Yunxian may be the oldest reliably dated hominin fossils in East Asia,” the research team writes. Only the skulls from Dmanisi in Georgia are older, at around 1.8 million years old. The short time interval between the finds from China and Georgia suggests that Homo erectus spread across Eurasia more quickly than previously assumed. “The finds from Yunxian indicate that Homo erectus must have advanced much further than just Dmanisi in Georgia around 1.77 million years ago,” say the researchers. At the same time, the new dating also reduces the time gap between the oldest potential tool marks from early humans in East Asia and the occurrence of Homo erectus.
However, some questions remain unanswered: “The mystery of exactly when Homo erectus first appeared in this region remains,” emphasizes co-author Christopher Bae from the University of Hawaii in Manoa. “As well as whether Homo erectus was really the first human species in some of these places in China and elsewhere in East Asia.” At 2.1 and 2.43 million years old, the artifacts discovered in Shangchen and Xihoudu, China, are significantly older than all Homo erectus evidence in Eurasia and also older than the oldest fossil of this early human species in Africa. This raises the question of who left these artifacts behind. So far, Tu and his colleagues don’t have an answer to this either.
Source: Hua Tu (Shantou University, China) det al., Science Advances, doi: 10.1126/sciadv.ady2270