In an article recently published by Laura Kehoe, a PhD researcher in wildlife conservation and land use, she describes an interesting new behaviour discovered in chimpanzee populations that has left scientists intrigued. Using camera traps, her team was the first to witness chimps throwing rocks at the trunks of trees (Video Here) , a potentially symbolic behaviour which was later witnessed in separate populations.
Her team has developed two theories on what the behaviour might mean. The first, and much less interesting one, is that the act is part of male shows of strength. The large bang created by the impact could replace or add to the standard behaviour of banging ones feet and hands against tree trunks as a means of displaying dominance. As certain trees seem to been consistent targets for the rocks it may be that they simply produce a better sound.
The second theory is based off the observation that this behaviour is very similar to that of early humans. Very early on we would mark territories and pathways using piles of stones, and a build up of stones has been witnessed within hollow trees near some of the stone throwing sites, though they have not determined if said trees lie along the boundaries of a chimpanzee group’s territory. Additionally, they could be creating ‘sacred trees’ similar to those found across the West Africa in human cultures, usually marked with stone piles as well.
Chimps exhibiting behaviour similar to early humans is not an outlandish conclusion as they have repeatedly been seen using basic toolage, including stones as a means to crack open nuts and fruits. Laura Kehoe said in the article that the stone throwing: “was a repeated activity with no clear link to gaining food or status—it could be a ritual”. A study has also been published in the journal Nature on the topic.