Captive orangutans can use stone tools without minimal direction from humans, researchers reported today. Besides an affirmation of orangutan intelligence, the finding has implications for understanding how and when stone tool use evolved in ancient human ancestors.
The research was in two parts: One experiment took place at the Kristiansand Zoo in Norway, and another happened at the UK’s Twycross Zoo. The experiment in Norway tested whether orangutans (Pongo pygmaeus) would be able to hammer a stone core — a key step toward crafting a tool — and cut open a container using a sharp flint flake. The experiment in England tested whether the apes could learn the tasks by observing others do them. The team’s research is published in PLOS One.
“Our study shows that, despite the fact that orangutans do not use stone tools in the wild, they can use them when these are provided to them in captive settings,” said Alba Motes-Rodrigo, a researcher at the University of Lausanne in Switzerland and the study’s lead author, in an email. “Therefore, the fact that orangutans don’t use stone tools in the wild is due to a lack of need or opportunity (because they are mostly arboreal) rather than due to a lack of ability.”
The orangutans in Norway did use the concrete hammerstone — but only to strike the walls and floor of their enclosure, not the stone they were provided with. In the second experiment, in which they were given a ready-made flint flake, an ape named Loui successfully used it to cut open a silicone skin to access food. The researchers say it’s the first time an untrained, unenculturated orangutan has demonstrated the ability to cut objects. (“Enculturated” orangutans have been exposed to human social and material culture, meaning they might treat the objects differently than a completely wild ape.)
In England, three female orangutans were shown how to strike a stone to create a flint flake. After watching the demonstrations, an ape named Molly successfully struck the rock’s edge. No flakes came off the stone, though the strikes targeted the correct area.
“When presented with a human-made flake, a naïve orangutan spontaneously used it as a cutting tool to open a puzzle box, providing proof of concept that cutting (or piercing) using sharp-edged tools is within orangutans’ spontaneous repertoire,” the researchers wrote. “Overall, our findings suggest that two prerequisites for the emergence of early lithic technologies — lithic percussion and the recognition of sharp-edged stones as cutting tools — might be deeply rooted in our evolutionary past.”
Motes-Rodrigo added in her email that, while the research doesn’t prove that the last common ancestor of orangutans and humans used tools, it shows 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.” In other words, the instinct to use tools may go back that far in our shared history, though no apes are known to knap rocks like humans can.
Evolutionary biologist Sofia Forss noted in an email that the apes, by virtue of living in a zoo, may have been exposed to human activities, including our use of various objects, even if they’d not been trained specifically to use stone tools. “We are still left with the critical question to why this behaviour does not occur in wild apes,” wrote Forss, who specialises in primatology at the University of Zurich. “Especially chimpanzees, despite their large tool use repertoire and terrestrial lifestyle.”
The team’s findings come on the heels of other tool news from the simian world: Last week, a study in Current Biology posited that chimpanzees may use insects for first aid, evidence of a unique application of resource as well as a demonstration of altruistic behaviour.
Primates are not the only animals that use tools — birds, pigs, and even crocodiles have shown the ability — but orangutans figuring out the same tools our ancestors relied on makes the species feel even closer to us than we already knew they were.