Humans are not the only beings that can identify rules in complex language-like constructions -- monkeys and great apes can do so, too, a study at the University of Zurich has shown. Researchers at the Department of Comparative Language Science of UZH used a series of experiments based on an 'artificial grammar' to conclude that this ability can be traced back to our ancient primate ancestors.

Stuart K. Watson, Judith M. Burkart, Steven J. Schapiro, Susan P. Lambeth, Jutta L. Mueller, Simon W. Townsend. Nonadjacent dependency processing in monkeys, apes, and humans. Science Advances, 2020; 6 (43): eabb0725 DOI: 10.1126/sciadv.abb0725

The ability to track syntactic relationships between words, particularly over distances (“nonadjacent dependencies”), is a critical faculty underpinning human language, although its evolutionary origins remain poorly understood. While some monkey species are reported to process auditory nonadjacent dependencies, comparative data from apes are missing, complicating inferences regarding shared ancestry. Here, we examined nonadjacent dependency processing in common marmosets, chimpanzees, and humans using “artificial grammars”: strings of arbitrary acoustic stimuli composed of adjacent (nonhumans) or nonadjacent (all species) dependencies. Individuals from each species (i) generalized the grammars to novel stimuli and (ii) detected grammatical violations, indicating that they processed the dependencies between constituent elements. Furthermore, there was no difference between marmosets and chimpanzees in their sensitivity to nonadjacent dependencies. These notable similarities between monkeys, apes, and humans indicate that nonadjacent dependency processing, a crucial cognitive facilitator of language, is an ancestral trait that evolved at least ~40 million years before language itself.

Fig. 1 Visual representation of each element and possible transitions between them for each sequence type (bracketed elements apply only to Non-AD condition), with examples.
Fig. 1 Visual representation of each element and possible transitions between them for each sequence type (bracketed elements apply only to Non-AD condition), with examples. - Numbers below category label indicate possible pitch variants. Y axis values in Familiarization row refer to pitch variant 1 of each element. Arrow color represents sequence transitions corresponding to a grammar (AXB and CXD) (see table S1 for summary of all possible sequence configurations per condition).