Many of the complex behaviours of humans involve the production of nonadjacent dependencies between sequence elements, which in part can be generated through the hierarchical organization of sequences.
To understand how these structural properties of human behaviours evolved, we can gain valuable insight from studying the sequential behaviours of nonhuman animals. Among the behaviours of nonhuman apes, tool use has been hypothesised to be a domain of behaviour which likely involves hierarchical organization, and may therefore possess nonadjacent dependencies between sequential actions.
In the Press
Study shows that chimpanzees perform the same complex behaviours that have brought humans success
University of Oxford
Chimps, Like Humans, Break Down Complex Tasks into Smaller Pieces
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Chimp video shows one of the most complex tool-use behaviours by wild animals ever documented
BBC Wildlife
“As humans, we perform many complex behaviours that involve complicated sequences – things like organising words into sentences or organising actions into highly technical processes of tool manufacturing and use.”
– Dr Elliot Howard-Spink, University of Oxford
For All Readers - AI Explainer
What is this research about?
This study explores how chimpanzees organize their actions during tool use, specifically focusing on whether their behaviors include nonadjacent dependencies—connections between actions that aren’t directly next to each other in a sequence. By studying these patterns, the researchers aim to understand the complexity of chimpanzee behavior and its implications for the evolution of human cognition and tool use.
What are nonadjacent dependencies, and why are they important?
Nonadjacent dependencies occur when one action in a sequence depends on another action further down the line, rather than the one immediately following it. These dependencies are often associated with hierarchical organization, where sequences are broken into smaller, structured subroutines. This is a hallmark of human behaviors like language and complex tool use, making it a key area to study in nonhuman primates to trace the evolutionary roots of such capabilities.
What did the researchers study?
The researchers analyzed wild chimpanzees as they cracked nuts using tools, a naturalistic and complex task. They measured patterns in the sequences of actions performed by the chimpanzees, using a statistical technique called mutual information (MI) to detect nonadjacent dependencies. They also compared these real-world action sequences to hypothetical models (called Markov models) that lack hierarchical organization.
What were the key findings?
- Nonadjacent Dependencies in Tool Use: About half of the adult chimpanzees showed evidence of producing nonadjacent dependencies at greater distances than predicted by non-hierarchical models.
- Hierarchical Organization: For most chimpanzees, their sequences of tool-use actions appeared to be organized hierarchically, with subroutines (small clusters of 2–8 actions) forming larger sequences. This supports the idea that their tool use involves structured planning, rather than random or linear sequences.
- Individual Variation: Not all chimpanzees exhibited the same patterns. Some showed alternative ways of organizing their actions, suggesting individual differences in their cognitive strategies for tool use.
What do these findings reveal about chimpanzee cognition?
The ability to produce nonadjacent dependencies and hierarchically organize sequences suggests that chimpanzees use complex cognitive systems during tool use. These behaviors might reflect domain-general cognitive skills, meaning they could apply similar strategies to other tasks beyond tool use.
What are the implications for human evolution?
This research supports the idea that hierarchical organization and nonadjacent dependencies—key features of human language and tool use—may have roots in the shared ancestry of humans and chimpanzees. The findings contribute to the hypothesis that the cognitive systems underpinning language and tool use evolved together in early hominins, potentially starting with behaviors like those observed in chimpanzees.
What’s next for this research?
Future studies will investigate whether other behaviors in chimpanzees (beyond tool use) also exhibit nonadjacent dependencies and hierarchical organization. This will help determine whether these abilities are specific to tool use or represent broader cognitive traits. The researchers also aim to explore whether similar patterns can be observed in other primates, which could shed light on the evolutionary pathways leading to human cognition.
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