“Whether it really represents ritualistic behavior is up for debate,” said Kalan. “Human ritual is already a contentious topic, so it’s hard to know what exactly we’re looking for when it comes to ‘rituals.’ We do think that the repeated, stereotyped behavior… by multiple individuals suggests there may be something more symbolic going on at these accumulative stone throwing sites.
”The study is “remarkable in its scope,” Dean told Ars—the researchers have data from 17 different sites, and they studied another 34 different chimp communities, a breadth that few studies manage. One element of the discovery that’s confusing, he added, is that it contradicts findings from experiments with captive chimps: studies have found that while humans are perfectly happy to copy actions when they can’t see the point of them (like ritual behaviors), chimps just want to get straight to the point. That makes it difficult to see how a ritualized behavior could develop in chimp society. “It’s a very interesting idea,” he said, but “I think … there’d need to be more investigation before we could really say it was that kind of ritualized behavior.” The “display” explanation, he added, is feasible.