A team of 80 international scientists, led by Hjalmar S. Kuhl and Ammie K. Kalan, both of which are from the Max Planck Institute in Germany, have been thrown into confusion after observing Chimpanzees in three West African countries such as Guinea Bissau, Côte d’Ivoire (the Ivory Coast), and Liberia, exhibiting strange behavior never before observed among chimps east of these countries.
According to their findings which were published in Scientific Reports, part of the journal Nature, the chimps were observed storing a great number of rocks in the hollows of trees.
Then, usually a male, takes one of the rocks, walks a distance away, grunts an utterance, and hurls the rock at the tree, leaving a mark on it. The rock is then placed back in the hollow to be reused in this manner again.
The team were able to make these observations by setting up camera traps in four remote locations in West Africa, where they caught footage of chimps taking part in this unusual and so far, unexplained behavior.
Chimps have been known to use rocks as tools, to bash open fruits or nuts for instance. Certain groups have even been seen using sticks removed of leaves and sharpened as spears, for hunting. These type of behaviors are mostly tied to survival.
However, according to the team's study, these unusual behaviors doesn't seem to have any connections to the animal's survival. It has nothing to do with acquiring food, mating, or furthering one’s status.
Researchers however, say it might be a unique display of male power, marking the border of their troop’s territory, or even a spiritual ritual.
The authors write, “We found four populations in West Africa where chimpanzees habitually bang and throw rocks against trees, or toss them into tree cavities, resulting in conspicuous stone accumulations at these sites.”
Over time, the researchers also found that this so-called ritualistic practice were mostly observed among the males, although few females were also found to be doing so too.
So could it be a spiritual ritual? Researchers on Kuhl and Kalan’s team have likened the rock pilings to the types of cairns the indigenous people of these areas make.
Cairns are piles of rocks that serve many purposes. People have been making them since the Stone Age. They can signify where a battle took place or as a memorial, as a marker for a grave site, a demarcation of territory, a signpost on a path, to denote a sacred site, and much more. This discovery transformed these four places from chimpanzee viewing areas to primate archaeological sites.
They wrote, "Stone accumulation shrines at ‘sacred’ trees are well described for indigenous West African peoples. Superficially, these cairns appear very similar to what has been described here for chimpanzee accumulative stone throwing sites, thus it would be interesting to explore whether there are any parallels between chimpanzee accumulative stone throwing and human cairn building, especially in regions of West Africa where the local environment is similar."
Study co-author Laura Kehoe made a statement that has caused something of an uproar in the scientific community, when she mused, “Maybe we found the first evidence of chimpanzees creating a kind of shrine that could indicate sacred trees.”