Chimps throw stones at trees amazing scientists

2016-03-08 19:00
Such accumulations of stones are only found in West Africa. (MPI-EVA PanAf/Chimbo Foundation)

Such accumulations of stones are only found in West Africa. (MPI-EVA PanAf/Chimbo Foundation)

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Leipzig - Scientists are mystified by West African chimpanzees that collect stones and throw them at trees, saying the wild primates seem to have taught themselves the never previously observed behaviour.

Scientists from the Leipzig, Germany based Max Planck Institute for Evolutionary Anthropology (MPI EVAN) say they placed camera traps at four chimpanzee research sites in West Africa where they had discovered conspicuous piles of stones next to trees.

The cameras caught individual chimpanzees - mostly adult males - picking up the stones and throwing them at the trees while emitting a "pant hoot," the account in the British journalScientific Reports says.

Most of what chimps do is about feeding and reproducing, whereas it remains unclear why they collect stones for this lobbing routine.

MPI EVAN's Hjalmar Kuehl said it could be a variation of hand-and-feet-drumming on tree roots, a behaviour found in all chimpanzee populations. The drumming's purpose, he said, is communicative as well as a typical ritualistic display by adult males.

Kuehl suggested that the accumulations of stones were reminiscent of cairns and could shed light on the origin of ritual sites in human evolution. He said further research was needed to interpret the chimpanzees' behaviour, which was observed in Liberia and Guinea.

Unlike instances of stone tool use by chimpanzees, its purpose isn't to locate or process embedded foods, the scientists noted. 

In a press release from MPI EVAN, Christophe Boesch, director of the institute's Department of Primatology, remarked: "As the stone accumulation behaviour does not seem to be linked to either the abundance of stones or the availability of suitable trees in an area, it is likely that it has some cultural elements."

The chimpanzees were filmed as part of a project to understand the ecological and evolutionary drivers of "culture" or behavioural diversification in chimpanzees, which, along with bonobos, are man's closest living relatives in the animal kingdom.

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