Eggshell beads made by hunter-gatherers 33,000 years ago used as a social network

The eggshell beads contain enough information to tell the story of their journey, if you know how to look.

Researchers recovered the beads in Lesotho, a small, mountainous country encircled by South Africa. And thousands of years ago its high elevation and wealth of rivers would have provided an imposing spot for hunter-gatherers to live.

Evidence of life at the site dates back to 85,000 years ago, meaning it sheltered hunter-gatherers through periods of climate change.

Despite the numerous ornaments they uncovered, there was no evidence that they were produced in the area, like eggshell fragments in progress. And there was no evidence that the eggs were laid in Lesotho because ostriches wouldn't typically live in that highland environment.

Modern hunter-gatherer societies, like those in southern Africa's Kalahari Desert, use ostrich eggshell beads to begin and maintain a relationship with other groups. The process is called hxaro, "kindling and cementing bonds within and between communities," according to a new study. The word hxaro has become synonymous with "beadwork" and "gifts."

So it stands to reason that the network exchanging them has a time-honored foundation. The researchers wanted to get to the heart of this social currency, finding out the time period and distances associated with them.

The beads were tested using a method called strontium isotope analysis to determine the point of origin for the shells, learning where they were originally laid.

Much like radiocarbon dating that analyzes the rate of decay of an element over time, the analysis relies on detecting strontium-87, the product of the radioactive element rubidium-87 as it decays.

Old rock formations including granite are found to have more strontium than younger rocks like basalt. And when animals eat grass from around these rocks, the strontium becomes part of their tissues.

Lesotho is at the heart of the Karoo Supergroup, a geologic formation with volcanic basalt at the center and older rings of rock stretching as far out as 202 to 621 miles away.

The researchers established a range of strontium isotopes by piecing together how much was available in a given area based on strontium content in soil and vegetation samples. They also used museum specimens, like rodent tooth enamel.

Their analysis revealed that 80% of the beads could not have originated from the Lesotho highlands. The study published Monday in the journal Proceedings of the National Academy of Science.

"These ornaments were consistently coming from very long distances," said Brian Stewart, study author and University of Michigan paleolithic archaeologist."The oldest bead in our sample had the third highest strontium isotope value, so it is also one of the most exotic."

His analysis showed that they could not have come from closer than 202 miles away, and may have first been made by hunter-gatherers as far as 621 miles away.

"Humans are just outlandishly social animals, and that goes back to [sharing this] information that would have been useful for living in a hunter-gatherer society 30,000 years ago and earlier," said Stewart. "Ostrich eggshell beads and the jewelry made from them basically acted like Stone Age versions of Facebook or Twitter 'likes,' simultaneously affirming connections to exchange partners while alerting others to the status of those relationships."

Stewart also believes the beads were exchanged during a time of climate shifts, between 25,000 and 59,000 years ago. This way, they could turn to each other when the weather worsened, sharing and pooling resources. Not only were the beads shared and exchanged over large distances, but also long periods of time. It hints at why modern humans survived.

"What happened 50,000 years ago was that the climate was going through enormous swings, so it might be no coincidence that that's exactly when you get this technology coming in," Stewart said. "These exchange networks could be used for information on resources, the condition of landscapes, of animals, plant foods, other people and perhaps marriage partners."