University of Tübingen: Orangutans show prerequisites for working with stone tools

The basic skills for using stone tools could be much more widespread among primates than previously thought: A study by the University of Tübingen, the Max Planck Institute for Evolutionary Anthropology in Leipzig and the University of Barcelona shows that orangutans spontaneously breed without prior training are able to recognize and use sharp stones as cutting tools. In this respect, they would even be superior to chimpanzees, which are more closely related to humans but had not shown this ability in corresponding experiments. The results were published in the journal PLOS ONE .

The results add another piece of the puzzle to the technological origins of our species, study leader Dr. Alba Motes Rodrigo and Dr. Claudia Tennie. As part of the EU-funded STONCULT project, the research team carried out tests with five untrained orangutans in two different European zoos. Puzzle boxes filled with food were put in front of the orangutans and sharp stone chips were also offered. When trying to open the boxes, an orangutan used the sharp stone chips as tools to open the puzzle box. They also made sharp stone flakes themselves by hitting stones on a hard surface, but did not use them any further.

The manufacture and use of sharp stone tools is considered one of the most important innovations in the evolution of our species. It allowed our hominid (primeval human) ancestors to incorporate nutritious foods into their diets, and it may have allowed other tools to be made and worked.

Research assumes that the systematic manufacture and use of such stone tools developed from a series of simple, basic behaviors and skills: In order to be able to manufacture stone tools, prehistoric people, so-called hominins, had to be able to use a suitable stone against striking another or against a hard surface to sever sharp pieces (stone chips). In order to use such a flake as a tool, they had to be able to recognize sharp stone edges as potential tools and be able to work on them.

The results of the current study show that these requirements – the use of sharp rocks as cutting tools and the ability to slam a rock against hard surfaces to create sharp chunks of rock – are present in orangutans. An earlier study had assumed that this would only be possible if these activities were previously demonstrated by humans.

“However, the orangutans in the study did not combine these skills to make and use their own stone tools,” says Motes-Rodrigo. “Even after people had demonstrated this. Only hominins seem to have possessed this ability to combine.”