A previously unknown type of human—jut-jawed, heavy-browed, deer-eating cave dwellers—may have been identified via Stone Age bones from southern China, according to a controversial new study.
The "mystery human fossils" might even represent an entirely new species that existed alongside our own as recently as 11,500 years ago, according to a team of Chinese and Australian researchers.
Or the fossils might represent an especially early migration of so-called modern humans out of Africa and into East Asia, the team suggests.
Or—as some critical scientists have said—the evidence may tell us something we already know: People come in all shapes and sizes.
Primitive Humans Held On Past Heyday?
"We have discovered a new population of prehistoric humans whose skulls are an unusual mosaic of primitive features, like those seen in our ancestors hundreds of thousands of years ago," evolutionary biologist Darren Curnoe of the University of New South Wales, said via email.
"In short, they're anatomically unique among all members of the human evolutionary tree," added Curnoe, a co-author of the new study of the "Red Deer Cave people," published online today in the journal PLoS ONE.
The study was principally based on the remains of at least three individuals from Maludong (or Red Deer Cave) in Yunnan Province (map)—fossils that had been excavated in 1989 but hadn't been studied until now.
Among the human remains was an abundance of bones from an extinct species of giant deer—suggesting the cave people were hunters with a taste for venison.
Stone and antler tools were also found, some of which were likely used to prepare the deer for dinner, researchers say.
The team also analyzed a partial skeleton found in 1979 in neighboring Guangxi Province. That human specimen had been encased in stone until the study team removed and reconstructed it.
(Read "Malapa Fossils: Part Ape, Part Human" in National Geographic magazine.)
The Red Deer Cave Look
The Red Deer Cave dwellers' unusual features included a flat face, a broad nose, a jutting jaw that lacked a chin, large molar teeth, a rounded braincase with prominent brow ridges, and thick skull bones, the researchers say.
Their brains were "moderate in size," Curnoe added.
Despite this seemingly primitive human design, radiocarbon dating of charcoal from the fossil deposits suggests the Red Deer Cave people lived just 14,500 to 11,500 years ago, the team says—a time by which all other human species, such as Neanderthals, are thought to have died out.
That date would make the Red Deer humans even more recent than the famous Homo floresiensis from the Indonesian island of Flores—itself a disputed potential human species. Discovered in 2003, the Flores "hobbits" are dated to no later than 13,000 years ago.
(Read "The People Time Forgot: Flores Find" from National Geographic magazine.)
Potential New Human Species?
The study team is so far reluctant to call their find a new human species.
"One of the major ongoing questions for scientists studying human evolution is the lack of a satisfactory biological definition of our own species, Homo sapiens," Curnoe said.
"This is one of the main reasons why we have been cautious about classifying the Red Deer Cave people at this time," he said.
Even so, Curnoe thinks "the evidence is slightly weighted towards the Red Deer Cave people representing a new evolutionary line.
"Their skulls are anatomically unique. They look very different to all modern humans, whether alive today or in Africa 150,000 years ago," the anthropologist said.
"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," Curnoe added.
"We might infer from this isolation that they either didn't interbreed or did so in a limited way," which would have staved off their "absorption" into the mainstream human lineage.
Alternatively, if these people were members of the wider Stone Age population in East Asia, they may represent an early and unknown dispersal of modern humans from Africa, the study team argues.
"The Red Deer Cave people might then sample an early migration to East Asia: people who interacted in a limited way, perhaps didn't contribute at all, to the founding populations of living East Asians," Curnoe said. (Also see "New Type of Human Discovered via Single Pinky Finger.")
"Nothing Extraordinary" About Mystery Humans
The team's suggestion that the Red Deer Cave people are somehow evolutionarily unique is receiving a skeptical reception from other scientists.
Physical anthropologist Erik Trinkaus described the findings as "an unfortunate overinterpretation and misinterpretation of robust early modern humans, probably with affinities to modern Melanesians"—indigenous peoples of Pacific islands stretching from New Guinea to Fiji (map).
"There is nothing extraordinary" about the newly announced fossil human, added Trinkaus, of Washington University in St. Louis, via email.
Philipp Gunz, of Max Planck Institute for Evolutionary Anthropology in Germany, isn't convinced by the study team's interpretation either.
"I would be surprised if it really was a new human group that was previously undiscovered," said, Gunz, also a physical anthropologist.
Responding to the criticism, study co-author Curnoe said, "That's fine. I would expect a mixture of comments."
It Takes All Kinds
The odd appearance of the Red Deer Cave people probably "just tells us that modern humans are a very diverse species," Max Planck's Gunz suggested.
"Modern humans are exceptionally variable, especially if you compare modern humans to our closest fossil relatives, the Neanderthals," who seem to have had a comparatively narrow range of appearances, he said.
While unusual, the skull features detailed in the new study "plot very close, or even within, the modern human range of variation," Gunz added.
"I would say it's not completely unexpected for a modern human at that age, so my gut feeling is that this is not a new species."
Gunz does, however, think the Chinese fossils might be evidence of multiple migration waves out of Africa that involved different populations of modern humans.
(Related: "China's Earliest Modern Human Found.")
To make a convincing case for their new human, the study team will need genetic evidence, Gunz said.
"It should be fairly easy to extract DNA from these fossils, and then we will know for sure how related they are to us as a modern human species," he said.
Attempts to obtain DNA from the Red Deer Cave remains haven't been successful to date, however.
New attempts are under way, "involving three of the world's major ancient DNA laboratories and cutting-edge techniques," according to study co-author Curnoe.
"We'll just have to wait and see."