In a new study, published this week in the journal Science Advances, apes and monkeys were able to track relationships between sounds the same way as humans, showing that this ability predates the evolution of language itself by at least 40 million years.
The ability to track syntactic relationships between words, particularly over distances, is a critical faculty underpinning human language, although its evolutionary origins remain poorly understood. Image credit: Nachosan / CC BY-SA 3.0.
Across the globe, humanity flourishes by sharing thoughts, culture, information and technology through language — an incredibly complex method of communication used by no other species.
Determining why and when it evolved is, therefore, crucial to understanding what it means to be human.
University of Warwick’s Professor Simon Townsend and his colleagues from Switzerland, Denmark, Germany, Austria and the United States made a crucial advance in our understanding of when a key cognitive building block of language may have evolved.
Being able to process relationships between words in a sentence is one of the key cognitive abilities underpinning language, whether those words are next to one another, known as an adjacent dependency, or distant to one another, known as a non-adjacent dependency.
For example, in the sentence ‘the dog who bit the cat ran away’ we understand that is it the dog who ran away rather than the cat, thanks to being able to process the relationship between the first and last phrases.
“Most animals do not produce non-adjacent dependencies in their own natural communication systems, but we wanted to know whether they might nevertheless be able to understand them,” said first author Dr. Stuart Watson, a researcher at the University of Zürich.
For their experiments, the scientists created artificial grammars in which sequences made up of meaningless tones instead of words were used to examine the abilities of subjects to process the relationships between sounds.
This made it possible to compare the ability to recognize non-contiguous dependencies between three different primate species, even though they do not share a common language.
The experiments were carried out with common marmosets, chimpanzees and humans.
The authors found that all three species were readily able to process the relationships between both adjacent and non-adjacent sound elements.
Non-adjacent dependency processing is, therefore, widespread in the primate family.
“The implications of this finding are significant,” said Professor Townsend, senior author of the study.
“This indicates that this critical feature of language already existed in our ancient primate ancestors, predating the evolution of language itself by at least 30-40 million years.”
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Stuart K. Watson et al. 2020. Nonadjacent dependency processing in monkeys, apes, and humans. Science Advances 6 (43): eabb0725; doi: 10.1126/sciadv.abb0725
