We’ve long known that chimpanzees, our closest evolutionary kin, have a penchant for using tools. Most wild chimpanzees use leaves, twigs and sticks to forage for food. Some chimp populations use stones as hammers and anvils to split open nuts. Others wield stone cleavers to slice through large fruits. As first observed by famed primatologist Jane Goodall, some male chimpanzees even hurl rocks and spears as displays of dominance.
For the most part, chimpanzees have been observed using tools for foraging purposes. But in 2016, a study in Nature described a bizarre, previously undocumented behavior among several chimpanzee populations in West Africa: throwing rocks at trees.
And because these tool-wielding apes were reusing the same sites, causing rocks to pile up around hollow tree trunks, the researchers suggested that the behavior is some sort of ritual.
