Scientists study stone tool making and use in orangutans

The first stone tools represent one of the most important technological milestones in human evolution. The production and use of sharp stone tools greatly expanded the ecological niche of our ancestors, allowing them to exploit new food resources. However, despite their importance, it is still unclear how these early stone technologies emerged and what behaviors served as stepping stones for the development of systematic stone tool production in our lineage. One approach to answering this question is to collect comparative data on the stone tool making and use capabilities of our closest living relatives, the great apes, to reconstruct potential stone-related behaviors of early hominids. . To this end, a team of researchers from the University of Tübingen, the Max Planck Institute for Evolutionary Anthropology, the University of Barcelona and the University of Oslo tested both learning abilities individual and social orangutans (Pygmy Pongo) making and using stone tools.

Loui, the juvenile male orangutan, uses the core as an active element to vertically strike the concrete floor of the test room. Image credit: Motes-Rodrigo et al., doi: 10.1371/journal.pone.0263343.

“Given their resistance to destructive taphonomic processes, the most abundant hominid artifacts in the archaeological record are stone tools,” said the lead author. Dr. Alba Motes-Rodrigo from the Department of Ancient Prehistory and Quaternary Ecology of the University of Tübingen and his colleagues.

“Early stone tools typical of Early Stone Age records include intentionally modified stones with sharp edges (e.g., shards and pits) and unmodified stone tools such as hammers and anvils dating 3.3 million years ago.”

“The production and use of these stone tools and later is often highlighted as a milestone in human evolution: stone tools expanded the ecological niche of early hominids by allowing, for example, butchery, meat processing, bone marrow extraction and plant tissue modification.”

“As a result, the production and use of stone tools has over time caused major changes in hominid dentition, hand morphology, and brain size.”

“However, despite the obvious ecological importance of stone tools in human evolution, how the skills associated with their production and use emerged and how they were learned by naïve individuals remains debated.”

In their research, Dr. Motes-Rodrigo and his co-authors used five untrained orangutans.

In the first experiment, they tested tool making and use in two captive male orangutans at Kristiansand Zoo in Norway.

Each orangutan was provided with a concrete hammer, a prepared stone core and two baited puzzle boxes requiring them to cut a rope or silicone skin in order to access a food reward.

The two orangutans spontaneously banged the hammer against the walls and floor of their enclosure, but neither aimed any blows at the stone core.

In the second experiment, the orangutans were also given a man-made sharp flint shard, which an orangutan used to cut through the silicon skin, thus solving the puzzle.

This is the first demonstration of cutting behavior in untrained, uncultured orangutans.

To find out if monkeys could learn the remaining steps by watching others, researchers showed how to strike the core to create a flint shard to three female orangutans at Twycross Zoo in the UK.

After these demonstrations, a woman continued to use the hammer to strike the core, directing the blows towards the edge as demonstrated.

This study is the first to report the spontaneous use of stone tools without narrow direction in orangutans that have not been cultured by humans.

“Our observations suggest that two major prerequisites for the emergence of stone tool use – striking with stone hammers and recognizing sharp stones as cutting tools – may have existed in our last common ancestor with orangutans, 13 million years ago,” the authors said.

“Our study is the first to report that untrained orangutans can spontaneously use sharp stones as cutting tools.”

“We also found that they readily engage in lithic percussion and that this activity sometimes leads to the detachment of sharp pieces of stone.”

the results appear in the newspaper PLOS ONE.

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A. Motes-Rodrigo et al. 2022. Experimental investigation of lithic and sharp stone percussion tool behaviors of orangutans. PLOS ONE 17 (2): e0263343; doi: 10.1371/journal.pone.0263343