Who Crafted Saudi Arabia’s 100,000-Year-Old Stone Tools?

BORDEAUX, FRANCE—A team of researchers led by Eleanor Scerri of the University of Bordeaux compared stone artifacts unearthed from three sites in the Arabian Desert with artifacts discovered in northeast Africa near the skeletons of modern humans. All of the tools were between 70,000 and 125,000 years old. Live Science reports that the artifacts from two of the three Arabian sites were “extremely similar” to the tools from northeast Africa, suggesting that the groups may have had some interaction, and that the Arabian tools could have been made by modern humans. The tools from the third Arabian site were “completely different,” however, and may have been crafted by a different human lineage. “It seems likely that there were multiple dispersals into the Arabian Peninsula from Africa, some possibly very early in the history of Homo sapiens. It also seems likely that there may have been multiple dispersals into this region from other parts of Eurasia. These features are what make the Arabian Peninsula so interesting,” Scerri explained. To see how this discovery might complement recent DNA work, see ARCHAEOLOGY's "Turning Back the Human Clock."

Turning Back the Human Clock

For years, archaeologists and geneticists have been troubled by the fact that their time lines for key events in human evolution don’t always match up. While archaeologists rely on the dating of physical remains to determine when and how human beings spread across the globe, geneticists use a DNA “clock” based on the assumption that the human genome mutates at a constant rate. By comparing differences between modern and ancient DNA, geneticists then calculate when early humans diverged from other species and when human populations formed different genetic groups.

The DNA clock is a powerful tool, but its conclusions—for example, that modern humans first emerged from Africa about 60,000 years ago—can disagree with archaeological evidence that shows signs of modern human activity well before that date at sites in regions as far-flung as Arabia, India, and China.

Now, new work, based on observation of the genetic differences between present-day parents and children, suggests that the genetic clock may actually run about twice as slowly as previously believed, at least for the last million years or so of primate history. In their review paper in the journal Nature Reviews Genetics, Aylwyn Scally and Richard Durbin of the Wellcome Trust Sanger Institute in Hinxton, England, propose much earlier dates for watershed events in human evolution, which could help bring the genetic and archaeological records in line. For instance, a slower clock places the migration of modern humans out of Africa at around 120,000 years ago, which is more consistent with archaeological evidence.

The revised clock also supports archaeological signs of modern human activity from more than 60,000 years ago at sites such as Jwalapuram, India (“Stone Age India,” January/February 2010), and Liujiang, China—evidence that has often been dismissed by geneticists as impossible. While more work is needed to confirm the findings, Scally says that archaeologists who work on such sites should be excited: “It can no longer be said that the genetic evidence is unequivocally against them.”