JUDY WOODRUFF: Now to an important finding of ancient fossils that could rewrite the latest thinking about human evolution and is the subject of scientific debate.
Jeffrey Brown has the story.
JEFFREY BROWN: The 1.8 million-year-old skull is the most complete ever found of a human ancestor from what's known as the human genus Homo.
It was unearthed in 2005 below a medieval village in the former Soviet republic of Georgia. Now, after eight years of research, the scientists who found it say it may show that human evolution followed a more straightforward line than has been thought and that fossils currently identified as different species may actually be variations within a single species.
DAVID LORDKIPANIDZE, Georgian National Museum: This new discovery shows that many features which we previously thought as variability and diversity could be lumped in one group.
JEFFREY BROWN: The skull was discovered with other partial remains, marking the earliest evidence of human ancestors moving out of Africa.
MAN: The species that we thought were different species in Africa now we realize probably are variants of the same species.
JEFFREY BROWN: Other scientists were more cautious in making that leap, though, even as they acknowledged that the new findings, published in the journal "Science," were spectacular, indeed.