Stick-ons for Stone Age tools.

Two stone implements dating to at least 36,000 years ago bear traces of a sticky black substance once used to attach them to a handle, according to a new report.

The discovery of the gluelike material, identified in chemical analyses as bitumen, pushes back substantially estimates of when adhesives were first used in tool making. Until now, the earliest evidence of this technique appeared at Middle Eastern sites no more than about 10,000 years old.

"These new data suggest that [Stone Age] people had greater technical ability than previously thought, as they were able to use different materials to produce tools," contend Eric Boeda of the University of Paris and his coworkers in the March 28 Nature.

The artifacts, which run from 2 inches to 3.5 inches in length, come from a site in the Syrian desert known as Umm el Tlel. Each was struck from a specially prepared lump of stone, a technique that became widespread between 35,000 and 100,000 years ago in North Africa and nearby Mediterranean regions.

Bitumen traces appear at convenient spots for attaching a handle to the sharp-edged stones, the researchers assert. Chemical features of the bitumen indicate that it was heated and applied to the implements as a glue, they say.

The new finds lie just below sediment dated at about 36,000 years old. If the artifacts were made 40,000 years ago or more, complex tool making has surprisingly ancient roots, writes Simon Holdaway, an archaeologist at La Trobe University in Bundoora, Australia, in an accompanying comment. If, however, the artifacts were made close to 36,000 years ago, members of a population wedded to traditional methods of tool production may have copied the adhesive innovations of a neighboring group, he suggests.

Either anatomically modern humans or Neandertals could have fashioned the Syrian tools, according to Holdaway.