Fossil may expose humanity's hybrid roots

 Last Nov. 28, archaeologists working in Portugal's Lapedo Valley, 90 miles north of Lisbon, chanced upon a child's burial. At first the researchers, led by Joao Zilhao of the Portuguese Institute of Archaeology in Lisbon, viewed the 24,500-year-old skeleton as an example of modern Homo sapiens.

 The shallow grave resembled other Late Stone Age human burials in Europe. A seashell lay among the child's bones, which bore the stains of an intentionally applied red pigment.

 By the time excavation of the skeleton concluded on Jan. 7, however, the scientists suspected that their find represented something far more interesting-an anatomical hybrid that could only have appeared so late as a result of extensive prior interbreeding between humans and Neandertals. H. sapiens and Neandertals both inhabited southwestern Europe for at least several thousand years, until around 30,000 years ago.

 The Portuguese team called in an authority on Neandertals, Erik Trinkaus of Washington University in St. Louis, to examine the find. He agreed that they had uncovered a hybrid kid.

 Zilhao announced the discovery at a press conference in Lisbon 2 weeks ago. Trinkaus described the skeleton last week in Columbus, Ohio, at the annual meeting of the Paleoanthropology Society. A full description of the new fossil will appear in Proceedings of the National Academy of Sciences.

"This kid surprised us," Trinkaus says. "The mosaic of anatomical features tells us that when Neandertals and modern humans met, they regularly interbred."

 Some researchers at the Columbus meeting who saw slides of the new specimen echoed Trinkaus' view. Others argued either that any interbreeding was minimal or that the fossil merely represents a stocky modern human.

 Much of the child's skull was crushed, although the scientists recovered braincase pieces and the lower jaw and teeth. The rest of the skeleton was largely intact. Tooth development places the child's age at between 3 1/2 and 5 years, Trinkaus notes. Radiocarbon analyses yielded the burial's estimated age.

 Modern human traits observed on the skeleton include a well-formed chin and relatively small lower arms. But the huge "snowplow" jaw, large front teeth, short legs, and broad chest betray a Neandertal heritage, Trinkaus says.

 The prehistoric child did not belong to a group of modern humans who may have evolved squat bodies suited to Ice Age conditions, he asserts. Southwestern Europe did not get cold enough to instigate such changes, in his opinion.

 Trinkaus suggests that Neandertals and modern humans interbred as closely related members of the same species, as some subspecies of baboons and other animals interbreed today.

 Scientists who argue that modern humanity arose simultaneously in two or more parts of the world over at least the past 1 million years support Trinkaus' interpretation. "The Portuguese find indicates that one anatomically variable human species inhabited western Europe," contends Milford H. Wolpoff of the University of Michigan in Ann Arbor. "Human populations have always interbred."

 Christopher B. Stringer of the Natural History Museum in London, a proponent of a theory of more recent human origins in Africa, disagrees. The fossil youngster may be an unusually stocky modern human, Stringer holds. Even if further analysis confirms its hybrid status, he suspects that prehistoric interbreeding rarely occurred. Numerous fossils of early modern humans show no signs of Neandertal contacts, Stringer notes.

 Another out-of-Africa advocate, Jeffrey H. Schwartz of the University of Pittsburgh, views the fossil child as a modern human who possibly suffered growth abnormalities that created a bulky lower body. "I don't see any evidence of hybridization," Schwartz remarks.