Orangutans wielding sharp stone tools have proven to scientists that they instinctively know how to use them as without being trained they began using flint flakes to cut their way into food puzzles. In the wild orangutans don’t use stone tools, meaning as an instinctive behavior it provides new insights into the evolution of stone tool use among our hominin ancestors.

The great apes showed off their skills in a study published in the journal PLOS ONE, in which researchers wanted to see if or how some captive orangutans could employ a range of stone tools with and without instruction.

“Stone tool studies with untrained apes allow us to build a more informed hypothesis about which skills our extinct hominin ancestors might have had,” lead author Alba Motes-Rodrigo of the Department of Early Prehistory and Quaternary Ecology at the University of Tübingen, Germany, told IFLScience.

“These types of studies also help us understand how stone technologies initially emerged and which stone-related behaviours served as stepping-stones for the development of intentional sharp stone-tool production and use in our lineage.”

Orangutans come in handy in such research because they are proficient tool users in the wild, just not with stones. This means captive animals can be assumed to be unlearned in the art of stone tool craft, allowing the researchers to investigate the learning process of stone-related skills from the beginning.

As one does when working with strong apes, the researchers gave some orangutans hammers and a blunt stone core to see if they could get into a baited puzzle. They were required to cut a rope or silicon if they were going to reach the food prize.

While the two animals went to town with their hammers in hitting their enclosure, neither tried to shape the stone core so they could hack their way into the puzzle.

However, when given a human-made flint flake one orangutan, Loui, proved he instinctively knew how to use a sharp stone tool to cut through to the food. This marks the first time cutting behavior has been demonstrated in this way by an untrained orangutan.

Furthermore, when three orangutans were shown how to turn a blunt rock into a sharp tool by hitting it with another stone, one began mimicking the behavior using lithic percussions to hit the stone core as demonstrated.

“Our results have added a new piece to the puzzle of the technological origins of our species showing that an ape species — that does not use stone tools in the wild and that diverged from our lineage 13 million years ago — spontaneously engages in stone-related behaviours crucial for stone tool making (lithic percussion),” Motes-Rodrigo concluded, “[and] has the ability to recognise and use sharp stones as cutting tools, which had never been reported in an untrained ape before.”

I guess that shifts us into the Rise of the Planet of the Apes era.