In a compelling new study that may rewrite our understanding of language evolution, researchers have discovered that wild orangutans vocalize with a recursive structure previously thought to be unique to human language. The findings suggest that the origins of complex, layered communication may stretch back far deeper in evolutionary history than previously believed.
The research conducted by a team from The University of Warwick in collaboration with the University of Torino, builds on the long-standing idea that recursion. The nesting of phrases within phrases is a key component that sets human communication apart from all other animal vocalizations. Recursion allows us to construct infinite meaning from a finite vocabulary, as in the classic sentence.
But when scientists analyzed the alarm calls of female Sumatran orangutans in the wild, they uncovered a surprising depth of vocal structure.
“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,” explains Dr. Chiara De Gregorio, lead author on the research.
This layered structure emerged as orangutans combined individual vocal elements into small groupings, grouped those into larger bouts, and then further organized those bouts into even broader sequences. The result is a form of multi-layered vocal expression bearing striking similarity to recursive human speech patterns.
More intriguingly, this structure appeared to serve a functional purpose. When faced with different types of threats, orangutans varied the rhythm and regularity of their alarm calls. A genuine predator, like a tiger, prompted rapid and urgent vocalizations. In contrast, when presented with a visually startling but non-threatening object—such as a brightly colored cloth—the calls were slower and less rhythmically consistent.
This suggests that orangutans are not merely producing patterned noise, but actively encoding contextual information into a structured vocal system.
“This discovery shows that the roots of one of the most distinctive features of human language — recursion – was already present in our evolutionary past,” adds lead author Dr. De Gregorio. “Orangutans are helping us understand how the seeds of language structure might have started growing millions of years ago.”
While it has long been accepted that great apes share various social and cognitive traits with humans, the presence of structured recursive communication in wild orangutans pushes the timeline of language evolution back significantly. Since recursion leaves no trace in the fossil record, such discoveries are rare and valuable glimpses into the emergence of one of humanity’s defining traits.
This study was published by University of Warwick
