RENEE MONTAGNE, HOST:

Now, what if I told you that 33,000 years ago, the hunter-gatherer version of a Facebook like came in the form of a bead? White, creamy and looking a bit like a Cheerio, these beads were made from the eggshells of ostriches. A new study finds that people in the Kalahari in southern Africa exchange the ostrich-egg beads as a lavish and visible sign of, well, being friends.

BRIAN STEWART: These are not totally dissimilar to, you know, what we think of today in terms of social media, things like Facebook or Twitter likes. They reaffirm and cement bonds of friendship. And they advertise to others the status of those relationships.

MONTAGNE: Brian Stewart at the University of Michigan is one of the study's authors. He says these beads traveled many miles between Stone Age groups, given as gifts to ensure that, at some future time, if the group needed help, it would be waiting for them.

STEWART: And what this does is basically create kind of long-distance insurance policies, kind of webs of risk pooling across the landscape because when you enter into an exchange partnership with another person, what that's doing is allowing you mutual access to that person's territories.

MONTAGNE: So let's say your home turf is experiencing a drought. That bead bond could allow you to move your family to where the water is without being driven away. Stewart says this mutual cooperation over vast landscapes is one of the earliest examples of a distinctly human behavior. We ensure our species' survival by working together. Transcript provided by NPR, Copyright NPR.