In 1989, a femur and part of a skull were found in a cave in the southwestern Chinese province of Yunnan.
Radiocarbon dating performed in 2008 on the sediments where the fossils were found showed them to be around 14,000 years old — which would mean they came from a time when Homo sapiens (modern humans) were in many parts of the world had emigrated.
However, the primitive features of the bones bothered scientists who wondered what kind of people the fossils belonged to.
The shape of the skull resembled that of Neanderthals — an archaic human population that disappeared about 40,000 years ago — and it appeared the brains were smaller than modern humans.
As a result, some experts on human evolution thought that the skull probably belonged to a hybrid population of archaic and modern humans, or perhaps to a previously unknown human species that co-existed with our own. Researchers named the group the Red Deer People after the name of the cave where the remains were found.
Chinese scientists have now extracted genetic material from the skullcap and sequenced the DNA. They found that the skull belonged to a female who was most likely a direct human ancestor – a member of homo sapiens – not a hitherto unknown human type.
“The ancient DNA technique is a really powerful tool,” said Bing Su, a professor at the Kunming Institute of Zoology at the Chinese Academy of Sciences in Yunnan, which was involved in the research, in a press release. “It tells us quite clearly that, despite their unusual morphological features, the Red Deer Cave people were modern humans and not archaic species like Neanderthals or Denisovans.”
Su and his colleagues shared their findings in a study published Thursday in the journal Current Biology. Their analysis of the genome revealed the person to whom the bones belonged Neanderthals and Denisovans had ancestors similar to those found in modern humans – suggesting they were not part of a hybrid population that interbred with each other.
DNA from Denisovans, a poorly understood group of archaic humans, and Neanderthals lives on in some humans today. That’s because our ancestors of Homo sapiens encountered these groups long ago as they spread around the world, and bred with them.
The researchers compared the genome extracted from the ancient DNA to the genomes of other people from around the world – both modern and ancient.
They found that the bones belonged to an individual closely associated with East Asian Native American ancestry. Researchers believe this group of people traveled north to Siberia and then crossed the Bering Strait to become one of the first Americans.
“Their genome fills in a really important missing piece of the overall story of how humans came to America. Much work has been focused on the other branch of Native American ancestry – the Siberians – but not much was known prior to this paper on the East Asian ancestry of Native Americans. It’s really important to understand this branch because it makes up the majority of Native American ancestors!” said Jennifer Raff, a geneticist and anthropologist at the University of Kansas and author of Origin: A Genetic History of the Americas, per E-mail.
“I find their results plausible and very interesting. We’re still trying to figure out the geographic location of the populations directly descended from the first peoples, but this paper gives us some additional clues,” added Raff, who was not involved in the research.
But what explained the unusual morphological features of the remains?
The researchers described the genome as having “low coverage,” meaning it doesn’t contain enough detail to explain why the bones looked different modern human skeletons. Acidic soil and warm, humid conditions at the site where the skull was found meant the scientists were only able to recover 11.3% of the genome. It was the first time DNA has been sequenced from a human fossil found in southern China.
The study determined that the person to whom the bones belonged belonged had great genetic diversity, suggesting that a number of different lineages of early modern humans must have coexisted during the Late Stone Age in southern East Asia. Perhaps, the study suggests, the region had been a refuge during the height of the Ice Age.
“I know these fossils better than anyone. They’re very enigmatic anatomically, even if they’re modern humans, as the DNA suggests,” Curnoe, who wasn’t involved in the latest study, said via email.
“How do we reconcile that? Perhaps the anatomical form of humans in the past – over long periods of time – was very ‘plastic’ and responsive to the environment and lifestyle of these early humans. This might be something we’ve lost since we started farming.”
Analysis of the Red Deer Cave genome could also help build a more complete picture of ancient people in East and Southeast Asia — an exciting place for paleoanthropologists.
Next, the Chinese team hopes to find additional support for their findings by sequencing older human DNA using fossils from Southeast Asia, particularly those that predate the Red Deer Cave people.