Fossils Could Point To New Human Species
March 15, 2012

Fossils Could Point To New Human Species

Lawrence LeBlond for

Scientists searching caves in China have unearthed the fossils of a possibly previously unknown species of human, including one that possesses a highly unusual mix of archaic and modern anatomical features found in humans.

The find is significant, as the fossils -- dating back to 14,500 to 11,500 years ago -- represent the youngest of their kind ever found in mainland East Asia, and the most recent human remains found anywhere in the world that do not closely resemble modern humans. Dating the fossils so recently implies that they would have shared the landscape with modern humans when China´s earliest farmers were first appearing.

Scientists believe the fossils are from at least four individuals, called the Red Deer Cave people, named for their apparent fondness for venison, and for the site where they were found.

Analysis of the discoveries was made by an international team of scientists led by Associate Professor Darren Curnoe, of the University of New South Wales, and Professor Ji Xueping of the Yunnan Institute of Cultural Relics and Archeology. The team reported their findings in the journal PLoS One.

The team said that before the fossils can be ascribed to a new human lineage, a more detailed analysis is required.

“We´re trying to be very careful at this stage about definitely classifying them,” Curnoe told Jonathan Amos of BBC News. “One of the reasons for that is that in the science of human evolution or palaeoanthropology, we presently don´t have a generally agreed, biological definition for our own species (Homo sapiens), believe it or not. And so this is a highly contentious area.”

The remains of at least three of the individuals were found by Chinese archaeologists at Maludong -- Red Deer Cave -- near the city of Mengzi in Yunnan Province in 1989. The fossils went unstudied for nearly 20 years, when, in 2008, the 11-institution team began analyzing them. A fourth skeleton was found in 1979 in a cave near the village of Longlin, in Guangxi Zhuang Autonomous Region.

The skulls and teeth from both caves are strikingly similar to each other and show some modern anatomical features, as well as some previously unseen characters. The individuals had rounded brain cases with prominent brow ridges. The skull bones were quite thick and their faces were short and flat and tucked under the brain.

They had broad noses and their jaws jutted forward but they lacked a modern human-like chin. X-ray scans of their brain cavities indicate they had modern-looking frontal lobes but rather archaic-looking anterior lobes. They also had large molar teeth.

Curnoe and his colleagues posed two possible scenarios for the origin of the Red Deer Cave people.

The first hypothesizes that they represent a very early migration of primitive-looking Homo sapiens that lived separately from other forms in Asia before dying out. The second theory contends that they were in fact a distinct population of Homo sapiens that evolved in Asia and lived alongside modern humans.

Some scientists not connected with the research have suggested that the Red Deer Cave people are actually hybrids.

“It´s possible these were modern humans who inter-mixed or bred with archaic humans that were around at the time,” explained Dr. Isabelle De Groote, a palaeoanthropologist from London´s Natural History Museum. It is also possible that “they evolved these more primitive features independently because of genetic drift or isolation, or in a response to an environmental pressure such as climate.”

Curnoe acknowledged that any of these scenarios were “certainly possible.”

However, he told Ian Sample of The Guardian that he believed the “the evidence is slightly weighted towards the Red Deer Cave people representing a new evolutionary line. First, their skulls are anatomically unique. They look very different to all modern humans, whether alive today or in Africa 150,000 years ago.”

“Second, the very fact they persisted until almost 11,000 years ago, when we know that very modern looking people lived at the same time immediately to the east and south, suggests they must have been isolated from them. We might infer from this isolation that they either didn't interbreed or did so in a limited way,” he added.

Now, scientists are trying to extract DNA from the remains to get a clearer picture of their place in the history of human evolution. DNA could yield information about interbreeding, just as genetic studies have on the closely related human species: the Neanderthals and an enigmatic group of people from Siberia known as the Denisovans.

“We´ve had one attempt already, but without success,” said Curnoe. “We´ll just have to wait and see if we´re successful in our future work.”

Curnoe said it is also possible that the Red Deer Cave people could show through DNA testing evidence of hybridization with the mysterious Denisovans.

Marta Mirazón Lahr, an evolutionary biologist at Cambridge University, said she is convinced the remains are from modern humans. Their unusual features suggest Red Deer Cave people are either “late descendants of an early population of modern humans in Asia” or a very small population that developed the traits through a process known as genetic drift, she told Sample.

Whatever their true place on the evolutionary tree, the Red Deer Cave people are a significantly important find simply because of the scarcity of well dated, well preserved, and well described specimens from this region of the world, said Curnoe.

“The Red Deer People were living at what was a really interesting time in China, during what we call the epipalaeolithic or the end of the Stone Age,” said Curnoe. “Not far from Longlin, there are quite well known archaeological sites where some of the very earliest evidence for the epipalaeolithic in East Asia has been found.”

“These were occupied by very modern looking people who are already starting to make ceramics - pottery - to store food. And they´re already harvesting from the landscape wild rice. There was an economic transition going on from full-blown foraging and gathering towards agriculture,” he added.

It remains unclear how the Red Deer Cave people fit into this picture, but the research team promises they will report further findings on stone tools and other cultural artifacts also discovered at the sites.

Carbon dating of charcoal found with the fossils helped scientists establish their age. The charcoal itself showed the people knew how to use fire; and stone artifacts suggest they were toolmakers.

Fossil hunters also found remnants of various mammals at the Maludong dig site, all of which are species still around today, except for the giant red deer, the remains of which were found in abundance. “They clearly had a taste for venison, with evidence they cooked these large deer in the cave,” Curnoe said.

The Red Deer Cave people survived through the “They survived the final and one of the worst cold episodes, known as the Last Glacial Maximum, which ended around 20,000 years ago,” said Curnoe. “The period around 15,000 to 11,000 years ago when they thrived in southwest China is known as the Pleistocene-Holocene transition, and it saw a shift to climates and ecological communities the same as those of today,” he added.

“This time also saw a major shift in the behavior of modern humans in southern China, who began to make pottery for food storage and to gather wild rice – this marks some of the first steps towards full-blown farming,” Curnoe said. “The Red Deer Cave People were sharing the landscape with these early pre-farming communities, but we have no idea yet how they may have interacted or whether they competed for resources.”

Although modern-day Asia contains more than half the world´s population, researchers know little about humans there after our ancestors settled Eurasia some 70,000 years ago. No human fossils less than 100,000 years old had been found in mainland East Asia that resembled anything other than anatomically modern humans until now, Curnoe explained. The findings are fossil evidence that this region may not have been devoid of our evolutionary cousins.

“The discovery of the Red Deer Cave People opens the next chapter in the latest stage of the human evolutionary story, the Asian chapter,” Curnoe said. "“It´s a story that´s just beginning to be told.”