Asian trek: fossil puts ancient humans in Far East.

Researchers have unearthed a 40,000-year-old partial human skeleton in a northern Chinese cave. This rare find underscores the vast distances covered by human groups that left eastern Africa starting around 60,000 years ago. It also intensifies debate about whether prehistoric people replaced or interbred with humanlike species encountered during migration.

In 2001, tree-farm workers discovered a few bones from the ancient skeleton at Tianyuan Cave, located 56 kilometers southwest of Beijing. Chinese paleontologists led by Hong Shang of the Chinese Academy of Sciences in Beijing then excavated the site in 2003 and 2004.

Finds included limb bones, a lower jaw, and a few teeth from one individual. The lack of a preserved pelvis obscures the individual's sex. Investigators found no stone artifacts or other cultural remains at the site.

Radiocarbon measurements of one of the specimen's leg bones and of animal bones at the site provided an age estimate.

In an upcoming Proceedings of the National Academy of Sciences, Shang and his coworkers describe a mix of modern-human and so-called archaic skeletal traits. This anatomical mosaic reflects inter-breeding between ancient-human immigrants and humanlike species that already inhabited eastern Asia, in the researchers' view.

"As early modern humans spread out of eastern Africa, they interbred with other [Homo] populations [to different degrees]," says study coauthor Erik Trinkaus of Washington University in St. Louis.

The Chinese skeleton includes a jaw, legs, and arms that resemble those of people today. In contrast, its teeth and hand bones display features like those of the archaic Homo species known as Neandertals. These creatures inhabited Europe and western Asia from 130,000 to 30,000 years ago. Remains of eastern Asian Homo species from that period are too scarce to compare with the new find.

Only one other modern-human fossil in eastern Asia is as old as the Chinese skeleton. A skull found on Borneo in 1958 dates to between 45,000 and 39,000 years ago, report Graeme Barker of the University of Cambridge in England and his colleagues in the March Journal of Human Evolution.

Still, scientists disagree about whether modern humans interbred with Neandertals and other archaic Stone Age populations (SN: 3/24/07, p. 186).

Modern humans in eastern Africa may have initially evolved some archaic-looking traits on their own, suggests anthropologist Katerina Harvati of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Later generations that moved to Asia would have inherited those traits without interbreeding, she says.

However, too few fossils of modern humans from the period just before and during ancient migrations from Africa exist to test for this possibility.

"I will keep an open mind on the extent of hypothesized [interbreeding]," remarks anthropologist Chris Stringer of the Natural History Museum in London. For now, he suspects that little or no ancient inter-breeding occurred.

Aside from its controversial blend of traits, the Chinese skeleton displays the oldest known evidence of regular footwear use, Trinkaus says. The specimen's strong legs contrast with an unusually delicate toe that must have been protected from the stress of barefoot walking, he asserts.