A convergent interaction engine: vocal communication among marmoset monkeys

Abstract

To understand the primate origins of the human interaction engine, it is worthwhile to focus not only on great apes but also on callitrichid monkeys (marmosets and tamarins). Like humans, but unlike great apes, callitrichids are cooperative breeders, and thus habitually engage in coordinated joint actions, for instance when an infant is handed over from one group member to another. We first explore the hypothesis that these habitual cooperative interactions, the marmoset interactional ethology, are supported by the same key elements as found in the human interaction engine: mutual gaze (during joint action), turn-taking, volubility, as well as group-wide prosociality and trust. Marmosets show clear evidence of these features. We next examine the prediction that, if such an interaction engine can indeed give rise to more flexible communication, callitrichids may also possess elaborate communicative skills. A review of marmoset vocal communication confirms unusual abilities in these small primates: high volubility and large vocal repertoires, vocal learning and babbling in immatures, and voluntary usage and control. We end by discussing how the adoption of cooperative breeding during human evolution may have catalysed language evolution by adding these convergent consequences to the great ape-like cognitive system of our hominin ancestors. This article is part of the theme issue 'Revisiting the human 'interaction engine': comparative approaches to social action coordination'.

Keywords: babbling; convergence; cooperative breeding; intentional control over vocalizations; mutual gaze; turn-taking.

Figure 1.

The marmoset interaction engine. The marmoset interactional ethology is characterized by cooperative breeding, cooperation in various contexts and high levels of interdependence. To make this system work, adults and immatures face specific affordances, or behavioural tasks. To fulfil these tasks and affordances, a set of psychological and motivational adaptations must exist (see also [11,12]). These can be summarized as a marmoset interaction engine and include several of the elements that have been highlighted [19] as critical for the human interaction engine. They may thus scaffold more flexible communication not only in humans but also in marmosets. (Online version in colour.)

Figure 2.

Dissecting the primate origins of the human interaction engine. The human interaction engine can be viewed as composed of elements that are uniquely derived in humans (D) and elements that are shared with our closest living relatives (C), which are presumably homologous, with cooperatively breeding primates (A) which have presumably evolved convergently, and with other primates or non-primates (B). Since each species has a unique interactional ethology that overlaps more or less with that of humans, the same holds for the underlying interaction engines. The focus of this contribution was on elements that humans share with callitrichid monkeys and other cooperative breeders (A). These elements appear to be crucially involved in favouring communicative flexibility as reviewed above and, in the case of humans, the emergence of language. (Online version in colour.)