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A team from UNIGE, NCCR Evolving Language, reConnect and the Institut Pasteur shows that the vast majority of animal species have been vocalising at a shared rhythm for hundreds of millions of years.
From insects to great apes, by way of birds and fish, animals communicate through an extraordinary variety of sounds. Whilst the pitch or timbre of their vocalisations matters, rhythm may play a more fundamental role. Scientists from the University of Geneva (UNIGE), the NCCR Evolving Language, the reConnect Institute and the Institut Pasteur analysed more than 2,000 sound recordings produced by 98 animal species. All of them vocalise at a strikingly similar rate — roughly two to three acoustic events per second — regardless of their size, habitat, species or social complexity. This constraint is likely linked to the brain's capacity to process auditory stimuli, and human language is no exception. The findings are published in PLOS Biology.
Many animal species communicate using acoustic signals — calls, songs or vocalisations — that vary in frequency and tone. "But what about rhythm? Is there a common tempo, or does it adapt to the characteristics of each species? This temporal dimension is what we wanted to examine," says Anne-Lise Giraud, director of the reConnect Institute, researcher at the Pasteur Institute and adjunct professor in the Department of Basic Neurosciences at the UNIGE Faculty of Medicine and Director of the reConnect Institute at the Institut Pasteur, who led the research.
The scientists analysed sounds produced by 98 species — mammals, birds, amphibians, insects, reptiles and fish — by developing a method to calculate vocalisation rate in a uniform way and assess which parameters might influence it. "We found that 95% of species fall between 0.45 and 4.99 vocalisations per second, with a marked concentration around 2.8 Hz — a striking degree of homogeneity for animals that are otherwise so different," says Théophane Piette, postdoctoral researcher in the Department of Basic Neurosciences at the UNIGE Faculty of Medicine and first author of the study. "Neither body weight, lung capacity, social complexity nor habitat proved to be determining factors. This suggests that this rhythm is shaped by a shared, ancient constraint common across species, rather than by recent adaptations."
Humans are no exception to this universal pattern in the animal kingdom.
A neural explanation
To analyse a sound, the brain must simultaneously integrate its overall structure and its fine details. The researchers therefore propose that auditory systems evolved around two complementary timescales. Slow oscillations, particularly in the delta band (1–4 Hz), would provide a long integration window for tracking acoustic sequences and identifying the general structure of sounds — a rate that also corresponds to that observed across many animal vocalisations. Conversely, faster processes, likely in the low gamma bands, would enable fine-grained temporal discrimination and the analysis of detailed acoustic structure. These faster mechanisms would contribute in particular to the identification of individual speakers or sound sources.
Towards cross-species communication?
Humans are no exception to this universal pattern in the animal kingdom. Although our speech rate is slightly above the animal average — partly owing to the structuring of language into syllables, words and sentences — we spontaneously slow down in challenging communication situations: background noise, an elderly interlocutor, or a young child.
This shared rhythm may have another consequence: facilitating communication between species. If most animals transmit and receive at the same basic rate, they may be able to decode signals produced by other species. That's exactly what dogs do with their owners: they process human speech at this same slow rhythm, and humans in turn tend to slow their speech when addressing them. "This common tempo may not merely reflect how brains process sound; it could also constitute a kind of universal synchronisation that facilitates communication across species," concludes Théophane Piette.
This study is part of the work of the NCCR Evolving Language, co-directed by the universities of Geneva, Zurich and Neuchâtel, which aims to understand the biological foundations of language, its evolutionary origins and the challenges posed by new technologies.
