Early humans strung mollusc shells together to make jewellery at least 75,000 years ago. Archaeologists say the discovery of the Stone Age shell beads hint that people had advanced concepts of symbolism and language earlier than anyone realised.

There are two competing theories of how modern human behaviour emerged. One is that it evolved abruptly in Africa or Eurasia 40,000 to 50,000 years ago. A competing theory suggests it emerged gradually in Africa between 250,000 and 50,000 years ago.

The new study of Stone Age shells from the gastropod Nassarius kraussianus suggests the second theory is more likely. Several clusters of the shells have turned up in excavations at Blombos cave on the southern tip of South Africa since 1997.

They are about the size of peas and have a hole punched in them, almost always in the same position. And they come from a layer of sediments roughly 75,000 years old.

Now Christopher Henshilwood of the University of Bergen in Norway and his colleagues have analysed 41 of the shells, which were found in clusters of similar shade and size. They contain traces of ochre, thought to be used by Stone Age cave dwellers as a decorative pigment.

Worn edges
Under the microscope, the team found slightly worn, smoothed regions near the mouths of the shells and the pierced holes. These worn patches, which are not found on other natural shells, are consistent with the idea that they rubbed against thread, clothes or other shells.

That is compelling evidence, says Henshilwood, that the cave dwellers deliberately pierced the shells so they could string them together into necklaces or bracelets.

Blombos cave is famous for its abstract engravings on ochre from the same time period, and together with the beadwork, this suggests to Henshilwood that its inhabitants had a complex sense of symbolism.

To communicate the meaning of the symbols, the society must also have had well-developed language with some kind of grammatical structure, he believes.

Rosary beads
"They must have had a way of describing the symbolic message that the beads represent," he says. "If I were Catholic and you were not, and I wanted to explain to you how rosary beads are used to count prayers, it would be very hard to do that with sign language, or a grunt and a groan - you wouldn't get the message at all."

Even if people made the jewellery just to look pretty, that still represents a modern human desire not seen in the animal kingdom, says Henshilwood.

"The sheer number of these beads makes them very strong evidence that people were using symbolic behaviour very early," he says.

He suspects the craft emerged when people developed a taste for social climbing, exchanging gifts with their neighbours to win favours and priding themselves on their image.