Quote:Recursion is the repetition of language elements in an embedded way so that they form a comprehensible thought/phrase. Like Russian nesting dolls, the power of recursion mean we can combine a finite set of elements to deliver an infinite array of messages with increasing complexity.
It is widely believed that nested communication is a unique feature of human language, allowing us greater complexity of thought, but research from The University of Warwick, published today in Annals of The New York Academy of Sciences, tells a different story.
Dr. Chiara De Gregorio, Research Fellow at The University of Warwick, who performed this work alongside Adriano Lameira (also Warwick) and Marco Gamba (University of Torino), said: "When analysing the vocal data of alarm calls from female Sumatran orangutans, we found that the rhythmic structure of orangutans' sounds made were self-embedded across three levels -- an impressive third-order recursion. Finding this feature in orangutan communication challenges the idea that recursion is uniquely human."
The three-layered (recursive) structure of the orangutan's calls was as follows:

• Individual sounds made by orangutans occurred in small combinations (first layer)
  
• These combinations could be grouped into larger bouts (second layer)
  
• And these bouts could be grouped into even larger series (third layer), all with a regular rhythm at each level
  

https://www.sciencedaily.com/releases/2025/05/250516134254.htm