Thigh bone adds to mystery over 14,000-year-old Homo species

Leg fossil from Chinese cave raises controversial possibility of hybrid humans

bones from Red Deer Cave

THIGH PUZZLER  A newly described upper leg bone, shown here from two angles, from China’s Red Deer Cave (entrance shown, right) raises the controversial possibility that a now-extinct Homo species interbred with Homo sapiens, represented by these skull, jaw and tooth fossils from the same cave. 

D. Curnoe and Ji Xueping

A 14,000-year-old upper leg bone found in southwest China may come from a prehuman line of hominids that survived in East Asia long enough to mate with Homo sapiens, a controversial study concludes.

This partial limb contains an unusual mix of features that link it to various extinct members of the Homo genus, including Homo erectus from more than 1.5 million years ago, say paleoanthropologist Darren Curnoe of the University of New South Wales in Sydney and his colleagues. It’s difficult to assign a species to the Chinese specimen, but the bone doesn’t come from a modern human, the researchers assert December 17 in PLOS ONE.

The upper leg bone was discovered in Maludong, or Red Deer Cave. Curnoe’s team previously reported that skulls and teeth from that cave and nearby Longlin Cave belonged to an unusual-looking line of H. sapiens that may have interbred with an unidentified East Asian Homo species (SN: 4/7/12, p. 5). Critics charged that those fossils most likely represented an East Asian variant of modern humans.

Chinese scientists unearthed the cave finds in 1989. The fossils were stored in a Chinese museum and went unstudied until examined by Curnoe’s team.

The physical features of the Maludong limb, such as a narrow shaft with a thin outer layer of bone, look much more ancient than those of the skulls and teeth from the same cave, Curnoe says. It’s hard to know if the Maludong fossils represent a single H. sapiens population that included a lot of variation in its physical makeup. The fossils could also represent two separate species that lived side by side — H. sapiens and a now-extinct Homo species — or a genetic hybrid of the two, Curnoe cautions.

For instance, it’s possible that the Maludong leg fossil comes from a Stone Age Homo population in Asia, such as Neandertal relatives known as Denisovans or H. erectus, Curnoe adds. Occasional interbreeding could have occurred if relatively isolated populations of H. sapiens, represented by skulls and teeth in the caves, took refuge in southwest China’s tropics during recurring ice ages.  

Opinions vary on the significance of the Chinese fossils. Archaeologist Robin Dennell of the University of Exeter in England is in favor of an interbreeding scenario. He thinks the Maludong remains belong to a genetic hybrid of late H. erectus and early H. sapiens. H. sapiens reached southern China between 120,000 and 80,000 years ago (SN: 11/14/15, p. 15), leaving time for interbreeding with H. erectus, which survived in East Asia until around the same time, Dennell says.

But without more extensive comparisons of the Maludong leg bone with those of living and recent human populations, the Chinese fossil can’t be considered an example of interbreeding or a prehuman species, says paleoanthropologist Peter Brown of the University of New England in Armidale, Australia. Paleoanthropologist William Jungers of Stony Brook University in New York agrees. The bone, along with previous Maludong and Longlin finds, may well belong to a regional form of H. sapiens, making the new report “much ado about almost nothing,” he says.

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