The oldest fossil of a human skeleton found in China shows features that throw into question the theory that modern people evolved directly from African ancestors, a new study found.

The 40,000-year-old Tianyuan Cave skeleton, one of the oldest remains in Asia, has physical traits that match modern humans and the earlier Neanderthal people, researchers said in the Proceedings of the National Academy of Sciences yesterday.

The findings suggest that today’s humans evolved from both early modern people that migrated from Africa and archaic groups such as the Neanderthal. One theory of human development, sometimes called the “Out of Africa” theory, holds that modern people descended directly from African ancestors after a wave of migration between 100,000 and 40,000 years ago replaced earlier human species in Asia and Europe.

“This provides us with our first good fossil evidence for both the timing and the biology of early modern humans spread across Asia,” said Erik Trinkaus, one of the study’s authors and a professor of anthropology at Washington University in St. Louis. “Yes, they spread out of Africa, but as they did, they blended with populations that were already there.”

The research team, from Washington University and the Chinese Academy of Sciences, dated the Tianyuan Cave remains to between 38,500 and 42,000 years ago, making it one of the oldest pieces of fossil evidence for modern humans in Asia. The skeleton, excavated in 2003 and 2004, helps fill out the fossil record from Asia for the period when scientists believe modern humans spread from Africa to Europe and Asia.

The fossil’s physical characteristics, including the shape of the jaw and chin, shoulder joint, and ankle joint, clearly mark it as a modern human. Yet other traits, such as the skeleton’s tooth size, link it to Neanderthal humans, according to the study.

The evidence that the specimen shares features of both modern and archaic humans undermines the theory that modern humans were so superior to previous species that they simply replaced them, without interbreeding, according to Trinkaus.

“What this shows is that the difference in behavior and biology in these groups was not very great,” he said. “They basically saw each other as people, as appropriate mates.”

The study’s findings aren’t necessarily at odds with the theory of modern humans evolving from Africa, said Katerina Harvati, a specialist in modern human origins at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. The archaic traits probably represent premodern characteristics preserved in African modern humans, rather than absorbed from native populations in Asia and Europe.