Archaeologists have unearthed 270 pieces of engraved ostrich eggshell dated to around 60,000 years ago from a site called Diepkloof in South Africa’s Western Cape province. The fragments constitute what the researchers say is the “earliest evidence of a graphic tradition among prehistoric hunter-gatherer populations.” As such, the finds help to illuminate the emergence of symbolic representation—a hallmark of modern human behavior.

The Diepkloof artisans favored two patterns. The first motif, which occurs in the older levels at the site, is a hatched band that looks rather like a train track; the second motif, which decorates eggshell pieces from younger levels at the site, consists of a series of deeply engraved parallel lines. (The different colors of the fragments in the image above resulted accidentally from exposure to fire after the the engravings were made and the eggshell broke.) Because some of the fragments show evidence of punctured openings, the team posits that they are the remnants of containers. Recent Kalahari hunter-gatherers and other groups have been known to use the large, sturdy shells of ostrich eggs as flasks for storing water and other liquids.

"These items were used daily, were curated, and were elements of a collective and complex social life," Pierre-Jean Texier of the University of Bordeaux in France and his colleagues write in their paper describing the finds, published yesterday in the early online edition of the Proceedings of the National Academy of Sciences USA. "For these reasons ostrich eggshell provided an ideal surface for informative marking, such as self or group identification."

The Diepkloof eggshells are not the earliest examples of symbolism in the archaeological record. Blombos Cave in South Africa, for example, has yielded engraved red ochre, incised bone and pierced shells that were strung and presumably worn on the body—all from layers dated to 75,000 years ago;  three shell beads from Israel and Algeria are said to date to more than 100,000 years ago; dozens of pieces of red ochre--many of which were ground for use as pigment--turned up in layers dating to 165,000 years ago in a cave at Pinnacle Point in South Africa. What sets the Diepkloof discovery apart are the large number of pieces recovered (the 270 fragments are believed to represent a minimum of 25 containers and to span a few thousand years) and the standardization of the engravings.

The eggshells were found with stone tools made in the so-called Howiesons Poort cultural tradition that are themselves noteworthy. Many of the implements are made of a rock called silcrete, which the tool makers had to obtain from sources located 10 kilometers to more than 40 kilometers away.

Interestingly, no engraved eggshell turned up in the oldest Howiesons Poort levels at the site, nor in the youngest. Thus exactly where this eggshell-decorating custom came from and why it disappeared remain a mystery. But some researchers argue that symbolism should be expected to occur in fits and starts early on. According to their model, people only began to consistently engage in symbolic activities as population density increased, hence the fleeting nature of symbolic expression during times when population size was probably small.

Photograph courtesy of Pierre-Jean Texier, Diepkloof project.