Humpback whale song has long been recognised as a sophisticated form of social communication. But until now, no indicator made it possible to say that it had a statistical structure comparable to that of human language. This new study, published in Science, changes that. By applying methods drawn from developmental linguistics, the researchers have brought out that the song follows the same regularities as those observed in every known human language.
Tools inspired by language acquisition in humans
The methodological approach is the major innovation here. The interdisciplinary team, bringing together linguists, marine biologists, behaviour specialists and developmental scientists, drew on the mechanisms infants use to segment speech. The idea is simple: in humans, babies pick out words by analysing the transition probabilities between sounds. When those probabilities drop, it signals the boundary between two units.
By transposing this model to recordings of humpback whale song collected over eight years in New Caledonia, the scientists were able to extract repeating sequences obeying precise statistical distributions, never before observed in another animal species.
Universal regularities, shared by two distant species
Human language is culturally transmitted. It contains elements that recur, whose frequency follows a strongly skewed distribution. This pattern, known as Zipf’s law, makes learning and transmission between generations easier.
That is exactly what humpback whale song reveals. The analysis brought out recurring units, organised according to a probabilistic structure identical to that of language. This is not communication endowed with semantic meaning, but a structured system that could be compared to human music: rich, codified, but without a lexicon.
A cultural transmission comparable to that of language
What links humans and whales here is less the content of the message than the way it is learned, memorised, transmitted. This study shows that when complex behaviours are spread culturally, as song is in cetaceans or language in humans, they tend to take on regular structures that favour their persistence.
The finding opens the way to new hypotheses about the mechanisms of language evolution. It suggests that certain properties, long held to be exclusive to Homo sapiens, could result from universal constraints linked to cultural transmission.
Prospects on the convergent evolution of behaviour
For Professor Simon Kirby (University of Edinburgh), this study brings out a neglected point: the structure of language does not emerge solely from the need to express meaning, but also from the dynamics of learning and transmission.
By looking beyond our primate cousins, and by turning to cases of convergent evolution in other taxa, it becomes possible to reconsider the origins of language no longer as a singularity, but as an emergent product of animal culture.
Questions still open on the perception of the units
The study does not settle the essential question: are the units detected perceived as such by the whales themselves? The parallel with human babies is methodological, but nothing yet makes it possible to confirm that these structures have a cognitive existence in cetaceans.
Even so, the method opens up fresh prospects for the study of acoustic behaviour in non-human species, using the analytical tools developed for linguistics and the cognitive sciences.
Quotations from the researchers
“Revealing this hidden structure in whale song was unexpected, but it shows that this cultural behaviour offers a valuable insight into the evolution of complex communication in the animal kingdom.”
– Dr Ellen Garland, University of St Andrews
“This work shows how learning and cultural transmission can shape the structure of communication systems. This kind of statistical structure is likely to be found wherever a complex sequential behaviour is culturally transmitted.”
– Prof Inbal Arnon, Hebrew University of Jerusalem
“These results call into question long-standing assumptions about the uniqueness of human language, revealing deep commonalities between evolutionarily very distant species.”
– Prof Simon Kirby, University of Edinburgh
Article source: http://dx.doi.org/10.1126/science.adq7055
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