A distinct group of prehistoric people who lived in what is now south-west China more than 11,500 years ago could be a new human species, according to scientists who have completed a detailed analysis of their fossilised skeletons and skulls.
Researchers said the unique anatomy of what they call the "red deer cave people" meant they were either a very ancient tribe of Homo sapiens that had become isolated for tens of thousands of years from the rest of humanity, or a completely new human species.
A new species would add a further complication to the already complex story of human origins. It would mean there was a time when our own species, H. sapiens, shared the same non-African landscapes with at least four other human species until each in turn became extinct, allowing just one type of human to dominate the globe.
The red deer people hunted and cooked an extinct ice-age species of giant deer that lived in the area of Yunnan province in southern China. The remains of at least four red deer people, and their skulls, were excavated from two cave sites, one near the city of Mengzi in Yunnan and the other near the village of Longlin in the neighbouring region of Guangzi Zhuang.
Charred deer bones suggest that this extinct ice-age animal was a principal source of food, said Professor Darren Curnoe of the University of New South Wales in Australia, who carried out the study with Professor Ji Xueping of the Yunnan Institute of Cultural Relics and Archaeology, published in PLoS One, a journal produced by the Public Library of Science in the United States.
"The unique anatomy of the skulls of the red deer cave people shows they represent a previously unknown prehistoric population. They could be a new evolutionary line or a previously unknown modern human population that arrived early from Africa and failed to contribute genetically to living East Asians," Professor Curnoe said.
"We have dated the remains to between about 14,500 and 11,500 years ago, which means that these people are the youngest population to be found anywhere in the world whose anatomy doesn't comfortably fit within the range of modern humans," he said.
"While finely balanced, I think the evidence is slightly weighted towards the red deer cave people representing a new evolutionary line. They look very different to all modern humans, whether alive today or in Africa 150,000 years ago," Professor Curnoe added.
There were at least three other extinct human species living alongside H. sapiens in Europe and Asia, but until a decade ago only one of them was known to science – the Neanderthals, who inhabited a large territory extending from the Middle East to western Europe. Neanderthals lived from around 400,000 years ago until they became extinct about 30,000 years ago.
More recently, scientists discovered two more distinct human species that had lived outside Africa at the same time as H. sapiens. The Denisovans, who occupied a cave site at Denisova in the Altai Mountains of Siberia, died out about 40,000 years ago, while the miniature "Hobbits" (Homo floresiensis) lived on the Indonesian island of Flores until about 18,000 years ago.
The only other species of human found in Asia is the much older Homo erectus, which predated H. sapiens. While H. erectus emerged from Africa about 1.9 million years ago, H. sapiens migrated only about 70,000 years ago.
Professor Curnoe said the red deer people show little close similarity to any of these other humans species. "They don't show any particular resemblances to the Neanderthals. If anything, they show a mix of H. sapiens-like and H. erectus-like features, as well as some unusual traits," he said.
"Their skulls are an unusual mosaic of primitive features, like those seen in our ancestors hundreds of thousands of years ago, some modern traits, similar to living people, and several unusual features. In short, they're anatomically unique among all members of the human evolutionary tree," he said.
"The main ways they differ from modern H. sapiens are in their prominent brow ridges, thick skull bones, flat upper faces with a broad nose, and jutting jaws that lack a human-like chin," he added.
Further studies will clarify the type of stone tools these people used to hunt and butcher their quarry, which they cooked over fires. "They clearly had a taste for venison, with evidence they cooked these large deer in the cave," Professor Curnoe said.
They must also have been tough enough to survive the harsh climate at the end of the last Ice Age. "They survived the final, and one of the worst, cold episodes: the Last Glacial Maximum, around 20,000 years ago," he said.
"This time also saw a major shift in the behaviour 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."