Hjalmar S. Kuhl and Ammie K. Kalan have published a paper in Nature’s “Scientific Reports” documenting a never-before-seen behavior among chimpanzees in four West African populations. You can read their report here.
The authors hypothesize that the behavior they witnessed may hint at the beginnings of ritual and possibly even an awareness of the concept of the sacred among these chimps. NPR picked up the story and wrote their own piece, titled “Why Do Wild Chimpanzees Throw Stones at Trees?”
I have my own theory about this behavior:
There is a tree in my backyard with a small hole in it. The hole is roughly head-high and about the size of a regulation baseball. Also in my backyard, depending on the time of year, are many heavy black walnuts in their protective green sheaths. When held in the palm of the hand they have a really pleasing heft and they look like this:
As the green coverings split and rot away, the walnuts look more like this:
When these walnuts are on the ground, in either form, I cannot help but pick them up and throw them at the hole in the tree. It would be a waste of time to explain the set of rules that have developed over time for this one-person game. In the end, they are irrelevant. It is just something I do. The action has no religious or sociological meaning. It is simply deeply satisfying on a level far, far below intelligent thought.
Once every 100 throws or so, I’ll actually get a walnut in the hole. On those days, life is good.
I also throw rocks at a small circular orange bit of metal set on the end of a steel rod and marking the site of a fire hydrant on a path near Ithaca’s West Hill Community Garden. The metal disc is roughly the same size as the hole in the tree, as you can see here:
I walk my dogs in this area fairly often and by now they have gotten accustomed to waiting for me while I throw three stones—no more, no less—in an effort to hit the disk. Again, over time a set of rules has developed for this activity. And again, it would be a waste of time (and maybe even a bit alarming to you) if I were to explain them here. I have far less success at this challenge than I do with the walnuts and the tree. I have hit the disk a total of two times in hundreds and hundreds of attempts. On those days, life is great.
This feeling is all I need to understand what these chimps are doing.