Pika S, Wilkinson R, Kendrick KH, Vernes SC. 2018 Taking turns: bridging the gap between human and animal communication. Proc. R. Soc. B 285: 20180598. http://dx.doi.org/10.1098/rspb.2018.0598
Language, humans’ most distinctive trait, still remains a ‘mystery’ for evolutionary theory. It is underpinned by a universal infrastructure—cooperative turn-taking—which has been suggested as an ancient mechanism bridging the existing gap between the articulate human species and their inarticulate primate cousins. However, we know remarkably little about turn-taking systems of non-human animals, and methodological confounds have often prevented meaningful cross-species comparisons. Thus, the extent to which cooperative turn-taking is uniquely human or represents a homologous and/or analogous trait is currently unknown. The present paper draws attention to this promising research avenue by providing an overview of the state of the art of turn-taking in four animal taxa—birds, mammals, insects and anurans. It concludes with a new comparative framework to spur more research into this research domain and to test which elements of the human turn-taking system are shared across species and taxa.
9. The comparative turn-taking framework
The new framework enabling comparative, systematic, quantitative assessments of turn-taking abilities centres on four key elements characterizing human social action during conversation:(A) Flexibility of turn-taking organization(B) Who is taking the next turn?(C) When do response turns occur?(D) What should the next turn do?The first element—flexibility of turn-taking organization (A)—refers to the phenomena of varying size and ordering of turns and intentionality involved in human turn-taking sequences . The element mirrors the ability to voluntarily change and adjust signals/actions and thus the degree of underlying cognitive flexibility. It can be operationalized by quantifying the number, frequency and degree of repetition of signals and actions produced in turn-taking events, their combination (e.g. A-B-A; A-B-C), distribution of roles between participants (e.g. role reversal), and intentionality involved (e.g. goal persistence, sensitivity to the social context) [34,112,113].The second element—who is taking the next turn (B)—concerns who can or should produce the next signal and includes techniques for allocating turns to individuals or parties . Parameters should involve (i) body orientation towards recipient(s), (ii) gaze direction of signaller, (iii) response waiting, and (iv) whether recipient(s) can perceive the signal (e.g. being in the visual or auditory field).The third element—when do response turns occur (C)—addresses the time window or temporal relationship between an initiating turn and the response turn [10,24]. Since the normative timing of signal exchanges may differ across species, modalities, and transmission medium, a first mandatory step should be to establish typical time windows for a given species (see  for ideas to operationlize this element).The fourth element—what should the next turn do? (D)—concerns one of the most fundamental structures in the organization of human conversation: adjacency pairs . An adjacency pair can be recursively reproduced  and expanded in conversation and—in its minimal, unexpanded form—is composed of two turns, by different participants, that are adjacently placed, and are relatively ordered into first pair parts (actions that initiate some exchange, e.g. requests), and second pair parts (responsive actions, e.g. grants) . This element can be operationalized by testing whether subsequent turns qualify as adjacency pairs involving predictable signal-response sequences (e.g. a request gesture is typically responded with a granting signal; a call is typically responded with the same call type, e.g. common marmosets) [74,116].