Though most scholars in the field will probably accept the possibility of interbreeding, he said, a significant number will probably not.
The more ardent exponents of the out-of-Africa hypothesis of modern human origins may be holdouts. They have argued that early modern humans all emerged from Africa and wiped out the Neanderthal population in Europe. Whether the relationship was fraternal or genocidal has been much debated. But many have argued that the two groups were distinct, with humans displacing and probably slaughtering their rivals.
Dr. Chris Stringer, an expert on Neanderthals at the Museum of Natural History in London, who is a leader of the out-of-Africa forces, said that he was willing to consider the Portuguese findings with an open mind. He told The Associated Press that the current evidence was not sufficient to convince him of Dr. Trinkhaus's hybrid interpretation.
An alternative theory, known as regional continuity, holds that the earliest human ancestors arose in Africa and spread around the world more than a million years ago. Modern humans then emerged in different regions through separate evolution and interbreeding. A leading advocate of this theory is Dr. Milford Wolpoff, a paleontologist at the University of Michigan in Ann Arbor.
"This find should be devastating to the out-of-Africa people," Dr. Wolpoff said. "It shows their theory doesn't work, at least in Europe. And it shows that fundamentally, Neanderthals are the same species we are and they contributed their genes to European ancestry."
