Researchers have virtually reconstructed a crushed and distorted 1 million-year-old human skull discovered in China. The newly restored cranium may have belonged to a relative of the mysterious Denisovans and provides clues to the rapid evolution of Homo sapiens in Asia.
In a study published Thursday (Sept. 25) in the journal Science, researchers presented their reconstruction of the Yunxian 2 skull, which was excavated in 1990 from an archaeological site in Hubei province in central China.
After digitally reconstructing the Yunxian 2 skull using computed tomography (CT) scans, researchers noticed that it showed a distinctive combination of traits, including a large cranial capacity, a long and low frontal skull bone, and a narrow space between the eye sockets. This set of characteristics is found in what the researchers call the Homo longi clade, a lineage or group of individuals and their descendants that have the same ancestor.
“The Homo longi clade, containing the Denisovans, lasted for over a million years,” study co-author Chris Stringer, a paleoanthropologist at the Natural History Museum in London, told Live Science in an email. “But so did the Neanderthal and sapiens lineages.”
Based on statistical data from 57 fossil skulls, the researchers estimated that the Neanderthal clade diverged from a common human ancestor first, around 1.38 million years ago. Then, the H. longi clade diverged around 1.2 million years ago, followed by H. sapiens around 1.02 million years ago. (The earliest clear fossil evidence of H. sapiens, however, comes from 300,000-year-old bones from Jebel Irhoud in Morocco.) This short timeframe suggests that rapid diversification took place in all three human groups.
But the researchers are unsure what may have caused these ancient human groups to develop such diverse appearances so quickly. “They lived in small, relatively isolated populations and adapted to diverse paleoenvironments,” study co-author Xijun Ni, a paleoanthropologist at the Chinese Academy of Sciences, told Live Science in an email.
Pushing back the origin of these ancient human groups, however, means experts can look even earlier in time for factors that may have triggered human evolution.
“For example, there were two severe cold events at about 1.1 million and 900,000 years ago,” Stringer said, “and that may have catalysed evolutionary and behavioural changes,” including extinctions.
Given the 1 million-year-old date of the Yunxian 2 skull and its blend of ancient and modern physical traits, the researchers concluded in their study that it likely represents an early form of the group that includes the Denisovans.