Publications
Language has long been considered uniquely complex in the animal kingdom; however, recent research challenges which language capacities are uniquely human. Resolving how complex communication systems evolve requires accurate comparative assessment of animal communication. We propose a quantitative framework distinguishing combinatorial systems from simpler ones, identifying four transitions: signal combination versatility; learning and conventionalization; message expansion through combinatorial diversity; and syntax involving linear or hierarchical rules. These measurable transitions provide testable hypotheses for investigating whether generative communication evolved beyond humans.
Human language expands meaning through structured combinations of sounds, yet such mechanisms remain rare in nonhuman animals. To investigate meaningful combinatorial capacities beyond alarm contexts, we applied a quantitative, whole-repertoire approach to sooty mangabeys (Cercocebus atys). We recorded 1751 vocal utterances from two groups in Taï National Park, Ivory Coast. Using production context as a proxy for meaning, we examined two mechanisms: (1) bigrams, sequences of two different calls, and (2) iteration, recurrence of the same call type interspersed with others. Euclidean distance analyses revealed order-sensitive meaning in female bigrams combining ‘grunt’ and ‘twitter’. While single calls and ‘grunt_twitter’ frequently occurred during feeding, ‘twitter_grunt’ was predominantly associated with infant-directed affiliations. Iterative sequences such as ‘twitter_grunt_twitter’ also showed context-specific shifts, suggesting a role for iteration in meaning generation. These findings indicate that meaningful combinatorial capacities may extend beyond great apes and alarm contexts to socially benign interactions in monkeys. However, repertoire-wide use of meaning-shifting bigrams remains unconfirmed outside hominids.
The horizontal transmission of cultural knowledge is a powerful mechanism of evolutionary change1. Across taxa, group-specific cultural traditions are expressed in diverse contexts, such as foraging, tool use, self-care and socialization2. These traditions arise when group members converge on specific behavioral phenotypes. When these behavioral phenotypes involve communicative signals, such as gestures, they are termed dialects3. However, gestural dialects are rare in non-humans3. Behavioral phenotypes and traditions can also be lost, a well-documented phenomenon in humans4, but rarely documented in non-human animals5. Here, we find that chimpanzee gestures produced in copulation solicitations show culturally established phenotypes and undergo cultural loss due to human-induced population decline.
