In truth, the mtDNA studies are additionally problematic because the history of a single gene does not necessarily reflect the history of a population. Different genes can tell different stories, and mtDNA, as far as human evolution researchers are concerned, represents only one gene. Unfortunately, with regard to ancient DNA, the chances of recovering nuclear DNA (and thus other genes) from early human fossils with currently available techniques are quite slim. Fossils thus remain very much a part of the human origins debate.
Image: MILFORD H. WOLPOFF
EARLY MODERN EUROPEAN(center) shares more features in common with a Neandertal (left) than with a modern from the Middle East (right).
To that end, the second study published this month calling the Out of Africa replacement scenario into question focused on bones. According to their report in the January 12 Science, Milford H. Wolpoff of the University of Michigan and his colleagues set out to test the replacement theory by examining early modern human skulls from Central Europe and Australia dated to between 20,000 and 30,000 years old (above), searching for genetic input from more than one population. Both groups apparently exhibit traits seen in their Middle Eastern and African predecessors. But the early modern specimens from Central Europe also display Neandertal traits, and the early modern Australians showed affinities to archaic Homo from Indonesia. "These features amount to a smoking gun for continuity within these regions," says team member John Hawks of the University of Utah.
"Ancient humans shared genes and behaviors across wide regions of the world, and were not rendered extinct by one 'lucky group' that later evolved into us," Wolpoff asserts. "The fossils clearly show that more than one ancient group survived and thrived." Eventually, multiregionalists argue, Neandertals and other archaic humans as entities disappeared through interbreeding. (Other paleoanthropologists dispute the new data, noting that previous analyses of these same skulls have supported the replacement model.)
To be sure, the new findings will not end the decades-long debate over modern human origins. Where it will go from here, however, is anyone's guess.