If you’re looking for an accessory that never goes out of fashion, you can probably do no better than ostrich eggshell beads. The oldest known examples of these tiny, Cheerio-like decorations, found in rock shelters in Tanzania, have been dated to around 50,000 years ago, while similar creations are still made by San hunter-gatherers in Southern Africa’s Kalahari Desert today.
The beads are often the last of many incarnations of an ostrich egg, explains Brian Stewart, an archaeologist at the University of Michigan. After finding an egg, the San—presumably like ancient human ancestors—carefully drill a hole in it and drain the white and yolk to be eaten. Then they wash out the shell, which makes a handy water flask. When the canteen eventually breaks, people reduce the fragments down to a standard size, drill a hole in the middle of each, string them together, and then shape the fragments into rounded beads. The beads can then be strung together to make jewelry or sewn onto clothing for decoration. Ethnographers have found that the San often exchange the beads, sometimes with people who live 200 or more kilometers away, to help cement social connections.
Ostrich eggshell beads have also been found in other parts of Africa and in north Asia, places where, in general, people no longer make and trade them. Many have been discovered in rock shelter sites in Lesotho, a small, mountainous country that lies far to the southeast of the Kalahari, completely surrounded by South Africa. These beads were found in archeological layers that range in age from a few hundred years old to tens of thousands of years old, according to work by Stewart and others. It’s not known whether ostriches lived in Lesotho at the time the beads were made, Stewart notes, but it’s unlikely they did. “They really shouldn’t be up there in terms of their ecological preferences,” he says. “And certainly they’re not up there today.” So archeologists have long wondered whether the beads were “brought in or exchanged in from other areas. But they were never able to really test that.”
The oldest bead the team analyzed dates to about 33,000 years ago.
Stewart and his colleagues recently saw their chance to do such a test using strontium isotope analysis, which uses the ratio of strontium isotopes in a sample to trace organisms back to the geological environments where they originated. Lesotho is particularly well-suited to such an analysis because of its mountainous terrain surrounded by land that steadily decreases in elevation, with different types of rock—each with its own strontium ratio—dominating the surface at different levels. Because the ratios of strontium isotopes in eggshell and other animal remains reflect those of the rock and soil where they originated, researchers would be able to use this method to pinpoint where the beads came from.
There was a logistical hurdle the researchers would need to overcome, however: the group would need a large set of biological reference samples from multiple locations to create a strontium isotope map against which to compare the beads’ ratios. Assembling such a collection seemed like a Herculean task, but mulling over the problem, Stewart realized that such a collection already existed, albeit scattered across the back rooms of small natural history museums around South Africa. “They have these nice collections of small mammals . . . and they know exactly where they were taken from,” he says. “And, because they’re small mammals, they actually live in quite small, circumscribed territories.”
Comparing the isotope ratios from the animals’ teeth with those of eggshell beads from two Lesotho rock shelters, the group found that none had strontium signatures that matched the local geological strata, confirming that the beads didn’t come from local eggshells. Instead, “pretty much all of them came from no closer than 100 kilometers away . . . and about 20 percent of the beads came from further than about 200 or 250 or so kilometers away,” Stewart says. Of those, a smaller subset came from at least 300 kilometers away—but possibly much more, he adds. Determining the provenance of that well-traveled subset will require more work.
The oldest bead the team analyzed dates to about 33,000 years ago, and it happens to belong to the farthest-away subset. Combined with the climatic differences between verdant Lesotho and drylands to the west, and with what’s known about how the eggshell beads are exchanged today, the study’s results suggest the beads factored into savvy relationship-building, Stewart says. They “probably represent risk-hedging bets, or network[ing] attempts . . . on the part of desert hunter-gatherers who are trying to make . . . links with people that live up in the mountains where you’ve got more stable supplies of fresh water [and] of animals,” he says.
How the beads physically got there is another question. One possibility, Stewart says, is that they traveled through a series of exchanges among desert groups who lived tens of kilometers apart.
Ancient as some of them are, Lesotho’s ostrich beads are likely part of an older tradition of far-flung groups using goods to build social networks, perhaps as a way to ensure that they would receive help in tough times. “I think that gift exchange . . . is likely to have a much earlier origin,” Lyn Wadley, an archaeologist at the University of the Witwatersrand in Johannesburg, who was not involved in the study, writes in an email to The Scientist. Before ostrich shell beads came into fashion, “it may have operated through, for example, the early exchange of decorated eggshell flasks and marine shell beads.” Likewise, Stewart suspects that the small, uniform, mass-producible beads weren’t part of the first networking attempts, but represent “the end result of a longer process of evolution and becoming really flexible to difficult environments.”
While Wadley thinks the isotope evidence the authors present for the beads’ far-flung origins is compelling, she adds that the results don’t rule out an alternative explanation: that, rather than being gifted, the beads were brought to Lesotho during long-distance seasonal migrations.
Steven Kuhn, an anthropologist at the University of Arizona who was not involved in the research, also thinks it’s possible that the beads were transported long distances as personal possessions rather than gifts. But the authors’ explanation seems more plausible in light of what’s known about modern hunter-gatherers, he adds. Anthropologists have suspected that Homo sapiens long used a relationship-building strategy like the one laid out in the study to boost their chances of survival, he says.
Eggshell beads are compelling evidence for gift exchange, he notes, because they would have been easy for people to make locally if desired—even Lesotho residents probably wouldn’t have had to travel far to gather ostrich eggs from nearby deserts—so there was no other practical reason to exchange them with people from far away. He compares the behavior to today’s custom of businesses giving away calendars, pens, or fruit baskets. “Nobody really needs another calendar,” he says. “It’s more about establishing a relationship.”